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* [RFC/RFT 0/2] RISC-V: kprobes/kretprobe support
@ 2018-11-13 19:58 me
  2018-11-13 19:58 ` Patrick Stählin
                   ` (2 more replies)
  0 siblings, 3 replies; 18+ messages in thread
From: me @ 2018-11-13 19:58 UTC (permalink / raw)
  To: linux-riscv

Hi,

this is first version of kprobes/kretprobe support for RISC-V. Most of
the code is based on arm64 but obviously without the single-step
functionality.

It will insert a C.EBREAK instruction that is later being captured. The
only instruction supported at the moment is C.ADDISP16 as this sets-up
the stack frames for all the functions I've tested.

I've tested this on QEMU with multiple CPUs but don't have any real
hardware available for testing, and from experience that's when things
start breaking.

The plan is to expand compressed instructions to full ones and simulate
those to reduce the decoding overhead per intercepted call.

Please let me know if you have any objections to path I've chosen and
which instructions you absolutely need for a first version.

To enable this you need the following defines:

CONFIG_FUNCTION_TRACER=y
CONFIG_KPROBES=y
CONFIG_MODULES=y

The CONFIG_FUNCTION_TRACER is not strictly needed but makes testing
easier using debugfs.

After that, any example documented in 
Documentation/trace/kprobetrace.rst should work.

Patrick St?hlin (2):
  RISC-V: Implement ptrace regs and stack API
  RISC-V: kprobes/kretprobe support

 arch/riscv/Kconfig                            |   6 +-
 arch/riscv/include/asm/kprobes.h              |  30 ++
 arch/riscv/include/asm/probes.h               |  26 ++
 arch/riscv/include/asm/ptrace.h               |  34 ++
 arch/riscv/kernel/Makefile                    |   1 +
 arch/riscv/kernel/probes/Makefile             |   3 +
 arch/riscv/kernel/probes/decode-insn.c        |  38 ++
 arch/riscv/kernel/probes/decode-insn.h        |  23 +
 arch/riscv/kernel/probes/kprobes.c            | 401 ++++++++++++++++++
 arch/riscv/kernel/probes/kprobes_trampoline.S |  91 ++++
 arch/riscv/kernel/probes/simulate-insn.c      |  33 ++
 arch/riscv/kernel/probes/simulate-insn.h      |   8 +
 arch/riscv/kernel/ptrace.c                    |  99 +++++
 arch/riscv/kernel/traps.c                     |  13 +-
 arch/riscv/mm/fault.c                         |  28 +-
 15 files changed, 828 insertions(+), 6 deletions(-)
 create mode 100644 arch/riscv/include/asm/probes.h
 create mode 100644 arch/riscv/kernel/probes/Makefile
 create mode 100644 arch/riscv/kernel/probes/decode-insn.c
 create mode 100644 arch/riscv/kernel/probes/decode-insn.h
 create mode 100644 arch/riscv/kernel/probes/kprobes.c
 create mode 100644 arch/riscv/kernel/probes/kprobes_trampoline.S
 create mode 100644 arch/riscv/kernel/probes/simulate-insn.c
 create mode 100644 arch/riscv/kernel/probes/simulate-insn.h

-- 
2.17.1

^ permalink raw reply	[flat|nested] 18+ messages in thread

* [RFC/RFT 0/2] RISC-V: kprobes/kretprobe support
  2018-11-13 19:58 [RFC/RFT 0/2] RISC-V: kprobes/kretprobe support me
@ 2018-11-13 19:58 ` Patrick Stählin
  2018-11-13 19:58 ` [RFC/RFT 1/2] RISC-V: Implement ptrace regs and stack API me
  2018-11-13 19:58 ` [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support me
  2 siblings, 0 replies; 18+ messages in thread
From: Patrick Stählin @ 2018-11-13 19:58 UTC (permalink / raw)
  To: linux-riscv; +Cc: Patrick Stählin, Palmer Dabbelt, linux-kernel, Albert Ou

Hi,

this is first version of kprobes/kretprobe support for RISC-V. Most of
the code is based on arm64 but obviously without the single-step
functionality.

It will insert a C.EBREAK instruction that is later being captured. The
only instruction supported at the moment is C.ADDISP16 as this sets-up
the stack frames for all the functions I've tested.

I've tested this on QEMU with multiple CPUs but don't have any real
hardware available for testing, and from experience that's when things
start breaking.

The plan is to expand compressed instructions to full ones and simulate
those to reduce the decoding overhead per intercepted call.

Please let me know if you have any objections to path I've chosen and
which instructions you absolutely need for a first version.

To enable this you need the following defines:

CONFIG_FUNCTION_TRACER=y
CONFIG_KPROBES=y
CONFIG_MODULES=y

The CONFIG_FUNCTION_TRACER is not strictly needed but makes testing
easier using debugfs.

After that, any example documented in 
Documentation/trace/kprobetrace.rst should work.

Patrick Stählin (2):
  RISC-V: Implement ptrace regs and stack API
  RISC-V: kprobes/kretprobe support

 arch/riscv/Kconfig                            |   6 +-
 arch/riscv/include/asm/kprobes.h              |  30 ++
 arch/riscv/include/asm/probes.h               |  26 ++
 arch/riscv/include/asm/ptrace.h               |  34 ++
 arch/riscv/kernel/Makefile                    |   1 +
 arch/riscv/kernel/probes/Makefile             |   3 +
 arch/riscv/kernel/probes/decode-insn.c        |  38 ++
 arch/riscv/kernel/probes/decode-insn.h        |  23 +
 arch/riscv/kernel/probes/kprobes.c            | 401 ++++++++++++++++++
 arch/riscv/kernel/probes/kprobes_trampoline.S |  91 ++++
 arch/riscv/kernel/probes/simulate-insn.c      |  33 ++
 arch/riscv/kernel/probes/simulate-insn.h      |   8 +
 arch/riscv/kernel/ptrace.c                    |  99 +++++
 arch/riscv/kernel/traps.c                     |  13 +-
 arch/riscv/mm/fault.c                         |  28 +-
 15 files changed, 828 insertions(+), 6 deletions(-)
 create mode 100644 arch/riscv/include/asm/probes.h
 create mode 100644 arch/riscv/kernel/probes/Makefile
 create mode 100644 arch/riscv/kernel/probes/decode-insn.c
 create mode 100644 arch/riscv/kernel/probes/decode-insn.h
 create mode 100644 arch/riscv/kernel/probes/kprobes.c
 create mode 100644 arch/riscv/kernel/probes/kprobes_trampoline.S
 create mode 100644 arch/riscv/kernel/probes/simulate-insn.c
 create mode 100644 arch/riscv/kernel/probes/simulate-insn.h

-- 
2.17.1


_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

^ permalink raw reply	[flat|nested] 18+ messages in thread

* [RFC/RFT 1/2] RISC-V: Implement ptrace regs and stack API
  2018-11-13 19:58 [RFC/RFT 0/2] RISC-V: kprobes/kretprobe support me
  2018-11-13 19:58 ` Patrick Stählin
@ 2018-11-13 19:58 ` me
  2018-11-13 19:58   ` Patrick Stählin
  2018-11-13 19:58 ` [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support me
  2 siblings, 1 reply; 18+ messages in thread
From: me @ 2018-11-13 19:58 UTC (permalink / raw)
  To: linux-riscv

Needed for kprobes support. Copied and adapted from arm64 code.

Signed-off-by: Patrick St?hlin <me@packi.ch>
---
 arch/riscv/Kconfig              |  1 +
 arch/riscv/include/asm/ptrace.h | 34 +++++++++++
 arch/riscv/kernel/ptrace.c      | 99 +++++++++++++++++++++++++++++++++
 3 files changed, 134 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 55da93f4e818..b157ac82d486 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -43,6 +43,7 @@ config RISCV
 	select RISCV_TIMER
 	select GENERIC_IRQ_MULTI_HANDLER
 	select ARCH_HAS_PTE_SPECIAL
+	select HAVE_REGS_AND_STACK_ACCESS_API
 
 config MMU
 	def_bool y
diff --git a/arch/riscv/include/asm/ptrace.h b/arch/riscv/include/asm/ptrace.h
index 2c5df945d43c..70c0ad08ac08 100644
--- a/arch/riscv/include/asm/ptrace.h
+++ b/arch/riscv/include/asm/ptrace.h
@@ -16,6 +16,7 @@
 
 #include <uapi/asm/ptrace.h>
 #include <asm/csr.h>
+#include <linux/compiler.h>
 
 #ifndef __ASSEMBLY__
 
@@ -68,6 +69,7 @@ struct pt_regs {
 
 #define user_mode(regs) (((regs)->sstatus & SR_SPP) == 0)
 
+#define MAX_REG_OFFSET offsetof(struct pt_regs, orig_a0)
 
 /* Helpers for working with the instruction pointer */
 #define GET_IP(regs) ((regs)->sepc)
@@ -99,6 +101,17 @@ static inline void user_stack_pointer_set(struct pt_regs *regs,
 	SET_USP(regs, val);
 }
 
+/* Valid only for Kernel mode traps. */
+static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
+{
+	return regs->sp;
+}
+
+static inline unsigned long regs_return_value(struct pt_regs *regs)
+{
+	return regs->a0;
+}
+
 /* Helpers for working with the frame pointer */
 #define GET_FP(regs) ((regs)->s0)
 #define SET_FP(regs, val) (GET_FP(regs) = (val))
@@ -113,6 +126,27 @@ static inline void frame_pointer_set(struct pt_regs *regs,
 	SET_FP(regs, val);
 }
 
+extern int regs_query_register_offset(const char *name);
+extern unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs,
+					       unsigned int n);
+
+/**
+ * regs_get_register() - get register value from its offset
+ * @regs:	pt_regs from which register value is gotten
+ * @offset:	offset of the register.
+ *
+ * regs_get_register returns the value of a register whose offset from @regs.
+ * The @offset is the offset of the register in struct pt_regs.
+ * If @offset is bigger than MAX_REG_OFFSET, this returns 0.
+ */
+static inline unsigned long regs_get_register(struct pt_regs *regs,
+					      unsigned int offset)
+{
+	if (unlikely(offset > MAX_REG_OFFSET))
+		return 0;
+
+	return *(unsigned long *)((unsigned long)regs + offset);
+}
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_RISCV_PTRACE_H */
diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
index 60f1e02eed36..5b684e4ffc10 100644
--- a/arch/riscv/kernel/ptrace.c
+++ b/arch/riscv/kernel/ptrace.c
@@ -130,6 +130,105 @@ const struct user_regset_view *task_user_regset_view(struct task_struct *task)
 	return &riscv_user_native_view;
 }
 
+struct pt_regs_offset {
+	const char *name;
+	int offset;
+};
+
+#define REG_OFFSET_NAME(r) {.name = #r, .offset = offsetof(struct pt_regs, r)}
+#define REG_OFFSET_END {.name = NULL, .offset = 0}
+
+static const struct pt_regs_offset regoffset_table[] = {
+	REG_OFFSET_NAME(sepc),
+	REG_OFFSET_NAME(ra),
+	REG_OFFSET_NAME(sp),
+	REG_OFFSET_NAME(gp),
+	REG_OFFSET_NAME(tp),
+	REG_OFFSET_NAME(t0),
+	REG_OFFSET_NAME(t1),
+	REG_OFFSET_NAME(t2),
+	REG_OFFSET_NAME(s0),
+	REG_OFFSET_NAME(s1),
+	REG_OFFSET_NAME(a0),
+	REG_OFFSET_NAME(a1),
+	REG_OFFSET_NAME(a2),
+	REG_OFFSET_NAME(a3),
+	REG_OFFSET_NAME(a4),
+	REG_OFFSET_NAME(a5),
+	REG_OFFSET_NAME(a6),
+	REG_OFFSET_NAME(a7),
+	REG_OFFSET_NAME(s2),
+	REG_OFFSET_NAME(s3),
+	REG_OFFSET_NAME(s4),
+	REG_OFFSET_NAME(s5),
+	REG_OFFSET_NAME(s6),
+	REG_OFFSET_NAME(s7),
+	REG_OFFSET_NAME(s8),
+	REG_OFFSET_NAME(s9),
+	REG_OFFSET_NAME(s10),
+	REG_OFFSET_NAME(s11),
+	REG_OFFSET_NAME(t3),
+	REG_OFFSET_NAME(t4),
+	REG_OFFSET_NAME(t5),
+	REG_OFFSET_NAME(t6),
+	REG_OFFSET_NAME(sstatus),
+	REG_OFFSET_NAME(sbadaddr),
+	REG_OFFSET_NAME(scause),
+	REG_OFFSET_NAME(orig_a0),
+	REG_OFFSET_END,
+};
+
+/**
+ * regs_query_register_offset() - query register offset from its name
+ * @name:	the name of a register
+ *
+ * regs_query_register_offset() returns the offset of a register in struct
+ * pt_regs from its name. If the name is invalid, this returns -EINVAL;
+ */
+int regs_query_register_offset(const char *name)
+{
+	const struct pt_regs_offset *roff;
+
+	for (roff = regoffset_table; roff->name != NULL; roff++)
+		if (!strcmp(roff->name, name))
+			return roff->offset;
+	return -EINVAL;
+}
+
+/**
+ * regs_within_kernel_stack() - check the address in the stack
+ * @regs:      pt_regs which contains kernel stack pointer.
+ * @addr:      address which is checked.
+ *
+ * regs_within_kernel_stack() checks @addr is within the kernel stack page(s).
+ * If @addr is within the kernel stack, it returns true. If not, returns false.
+ */
+static bool regs_within_kernel_stack(struct pt_regs *regs, unsigned long addr)
+{
+	return (addr & ~(THREAD_SIZE - 1))  ==
+		(kernel_stack_pointer(regs) & ~(THREAD_SIZE - 1));
+}
+
+/**
+ * regs_get_kernel_stack_nth() - get Nth entry of the stack
+ * @regs:	pt_regs which contains kernel stack pointer.
+ * @n:		stack entry number.
+ *
+ * regs_get_kernel_stack_nth() returns @n th entry of the kernel stack which
+ * is specified by @regs. If the @n th entry is NOT in the kernel stack,
+ * this returns 0.
+ */
+unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs, unsigned int n)
+{
+	unsigned long *addr = (unsigned long *)kernel_stack_pointer(regs);
+
+	addr += n;
+	if (regs_within_kernel_stack(regs, (unsigned long)addr))
+		return *addr;
+	else
+		return 0;
+}
+
 void ptrace_disable(struct task_struct *child)
 {
 	clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
-- 
2.17.1

^ permalink raw reply	[flat|nested] 18+ messages in thread

* [RFC/RFT 1/2] RISC-V: Implement ptrace regs and stack API
  2018-11-13 19:58 ` [RFC/RFT 1/2] RISC-V: Implement ptrace regs and stack API me
@ 2018-11-13 19:58   ` Patrick Stählin
  0 siblings, 0 replies; 18+ messages in thread
From: Patrick Stählin @ 2018-11-13 19:58 UTC (permalink / raw)
  To: linux-riscv
  Cc: Patrick Stählin, Palmer Dabbelt, linux-kernel, Albert Ou,
	Oleg Nesterov

Needed for kprobes support. Copied and adapted from arm64 code.

Signed-off-by: Patrick Stählin <me@packi.ch>
---
 arch/riscv/Kconfig              |  1 +
 arch/riscv/include/asm/ptrace.h | 34 +++++++++++
 arch/riscv/kernel/ptrace.c      | 99 +++++++++++++++++++++++++++++++++
 3 files changed, 134 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 55da93f4e818..b157ac82d486 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -43,6 +43,7 @@ config RISCV
 	select RISCV_TIMER
 	select GENERIC_IRQ_MULTI_HANDLER
 	select ARCH_HAS_PTE_SPECIAL
+	select HAVE_REGS_AND_STACK_ACCESS_API
 
 config MMU
 	def_bool y
diff --git a/arch/riscv/include/asm/ptrace.h b/arch/riscv/include/asm/ptrace.h
index 2c5df945d43c..70c0ad08ac08 100644
--- a/arch/riscv/include/asm/ptrace.h
+++ b/arch/riscv/include/asm/ptrace.h
@@ -16,6 +16,7 @@
 
 #include <uapi/asm/ptrace.h>
 #include <asm/csr.h>
+#include <linux/compiler.h>
 
 #ifndef __ASSEMBLY__
 
@@ -68,6 +69,7 @@ struct pt_regs {
 
 #define user_mode(regs) (((regs)->sstatus & SR_SPP) == 0)
 
+#define MAX_REG_OFFSET offsetof(struct pt_regs, orig_a0)
 
 /* Helpers for working with the instruction pointer */
 #define GET_IP(regs) ((regs)->sepc)
@@ -99,6 +101,17 @@ static inline void user_stack_pointer_set(struct pt_regs *regs,
 	SET_USP(regs, val);
 }
 
+/* Valid only for Kernel mode traps. */
+static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
+{
+	return regs->sp;
+}
+
+static inline unsigned long regs_return_value(struct pt_regs *regs)
+{
+	return regs->a0;
+}
+
 /* Helpers for working with the frame pointer */
 #define GET_FP(regs) ((regs)->s0)
 #define SET_FP(regs, val) (GET_FP(regs) = (val))
@@ -113,6 +126,27 @@ static inline void frame_pointer_set(struct pt_regs *regs,
 	SET_FP(regs, val);
 }
 
+extern int regs_query_register_offset(const char *name);
+extern unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs,
+					       unsigned int n);
+
+/**
+ * regs_get_register() - get register value from its offset
+ * @regs:	pt_regs from which register value is gotten
+ * @offset:	offset of the register.
+ *
+ * regs_get_register returns the value of a register whose offset from @regs.
+ * The @offset is the offset of the register in struct pt_regs.
+ * If @offset is bigger than MAX_REG_OFFSET, this returns 0.
+ */
+static inline unsigned long regs_get_register(struct pt_regs *regs,
+					      unsigned int offset)
+{
+	if (unlikely(offset > MAX_REG_OFFSET))
+		return 0;
+
+	return *(unsigned long *)((unsigned long)regs + offset);
+}
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_RISCV_PTRACE_H */
diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
index 60f1e02eed36..5b684e4ffc10 100644
--- a/arch/riscv/kernel/ptrace.c
+++ b/arch/riscv/kernel/ptrace.c
@@ -130,6 +130,105 @@ const struct user_regset_view *task_user_regset_view(struct task_struct *task)
 	return &riscv_user_native_view;
 }
 
+struct pt_regs_offset {
+	const char *name;
+	int offset;
+};
+
+#define REG_OFFSET_NAME(r) {.name = #r, .offset = offsetof(struct pt_regs, r)}
+#define REG_OFFSET_END {.name = NULL, .offset = 0}
+
+static const struct pt_regs_offset regoffset_table[] = {
+	REG_OFFSET_NAME(sepc),
+	REG_OFFSET_NAME(ra),
+	REG_OFFSET_NAME(sp),
+	REG_OFFSET_NAME(gp),
+	REG_OFFSET_NAME(tp),
+	REG_OFFSET_NAME(t0),
+	REG_OFFSET_NAME(t1),
+	REG_OFFSET_NAME(t2),
+	REG_OFFSET_NAME(s0),
+	REG_OFFSET_NAME(s1),
+	REG_OFFSET_NAME(a0),
+	REG_OFFSET_NAME(a1),
+	REG_OFFSET_NAME(a2),
+	REG_OFFSET_NAME(a3),
+	REG_OFFSET_NAME(a4),
+	REG_OFFSET_NAME(a5),
+	REG_OFFSET_NAME(a6),
+	REG_OFFSET_NAME(a7),
+	REG_OFFSET_NAME(s2),
+	REG_OFFSET_NAME(s3),
+	REG_OFFSET_NAME(s4),
+	REG_OFFSET_NAME(s5),
+	REG_OFFSET_NAME(s6),
+	REG_OFFSET_NAME(s7),
+	REG_OFFSET_NAME(s8),
+	REG_OFFSET_NAME(s9),
+	REG_OFFSET_NAME(s10),
+	REG_OFFSET_NAME(s11),
+	REG_OFFSET_NAME(t3),
+	REG_OFFSET_NAME(t4),
+	REG_OFFSET_NAME(t5),
+	REG_OFFSET_NAME(t6),
+	REG_OFFSET_NAME(sstatus),
+	REG_OFFSET_NAME(sbadaddr),
+	REG_OFFSET_NAME(scause),
+	REG_OFFSET_NAME(orig_a0),
+	REG_OFFSET_END,
+};
+
+/**
+ * regs_query_register_offset() - query register offset from its name
+ * @name:	the name of a register
+ *
+ * regs_query_register_offset() returns the offset of a register in struct
+ * pt_regs from its name. If the name is invalid, this returns -EINVAL;
+ */
+int regs_query_register_offset(const char *name)
+{
+	const struct pt_regs_offset *roff;
+
+	for (roff = regoffset_table; roff->name != NULL; roff++)
+		if (!strcmp(roff->name, name))
+			return roff->offset;
+	return -EINVAL;
+}
+
+/**
+ * regs_within_kernel_stack() - check the address in the stack
+ * @regs:      pt_regs which contains kernel stack pointer.
+ * @addr:      address which is checked.
+ *
+ * regs_within_kernel_stack() checks @addr is within the kernel stack page(s).
+ * If @addr is within the kernel stack, it returns true. If not, returns false.
+ */
+static bool regs_within_kernel_stack(struct pt_regs *regs, unsigned long addr)
+{
+	return (addr & ~(THREAD_SIZE - 1))  ==
+		(kernel_stack_pointer(regs) & ~(THREAD_SIZE - 1));
+}
+
+/**
+ * regs_get_kernel_stack_nth() - get Nth entry of the stack
+ * @regs:	pt_regs which contains kernel stack pointer.
+ * @n:		stack entry number.
+ *
+ * regs_get_kernel_stack_nth() returns @n th entry of the kernel stack which
+ * is specified by @regs. If the @n th entry is NOT in the kernel stack,
+ * this returns 0.
+ */
+unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs, unsigned int n)
+{
+	unsigned long *addr = (unsigned long *)kernel_stack_pointer(regs);
+
+	addr += n;
+	if (regs_within_kernel_stack(regs, (unsigned long)addr))
+		return *addr;
+	else
+		return 0;
+}
+
 void ptrace_disable(struct task_struct *child)
 {
 	clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
-- 
2.17.1


_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

^ permalink raw reply	[flat|nested] 18+ messages in thread

* [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support
  2018-11-13 19:58 [RFC/RFT 0/2] RISC-V: kprobes/kretprobe support me
  2018-11-13 19:58 ` Patrick Stählin
  2018-11-13 19:58 ` [RFC/RFT 1/2] RISC-V: Implement ptrace regs and stack API me
@ 2018-11-13 19:58 ` me
  2018-11-13 19:58   ` Patrick Stählin
  2018-11-14  8:37   ` mhiramat
  2 siblings, 2 replies; 18+ messages in thread
From: me @ 2018-11-13 19:58 UTC (permalink / raw)
  To: linux-riscv

First implementation, adapted from arm64. The C.ADDISP16 instruction
gets simulated and the kprobes-handler called by inserting a C.EBREAK
instruction.

C.ADDISP16 was chosen as it sets-up the stack frame for functions.
Some work has been done to support probes on non-compressed
instructions but there is no support yet for decoding those.

The way forward should be to uncompress the instructions for simulation
to reduce the number of instructions used to decode the immediate
values on probe hit.

Signed-off-by: Patrick St?hlin <me@packi.ch>
---
 arch/riscv/Kconfig                            |   5 +-
 arch/riscv/include/asm/kprobes.h              |  30 ++
 arch/riscv/include/asm/probes.h               |  26 ++
 arch/riscv/kernel/Makefile                    |   1 +
 arch/riscv/kernel/probes/Makefile             |   3 +
 arch/riscv/kernel/probes/decode-insn.c        |  38 ++
 arch/riscv/kernel/probes/decode-insn.h        |  23 +
 arch/riscv/kernel/probes/kprobes.c            | 401 ++++++++++++++++++
 arch/riscv/kernel/probes/kprobes_trampoline.S |  91 ++++
 arch/riscv/kernel/probes/simulate-insn.c      |  33 ++
 arch/riscv/kernel/probes/simulate-insn.h      |   8 +
 arch/riscv/kernel/traps.c                     |  13 +-
 arch/riscv/mm/fault.c                         |  28 +-
 13 files changed, 694 insertions(+), 6 deletions(-)
 create mode 100644 arch/riscv/include/asm/probes.h
 create mode 100644 arch/riscv/kernel/probes/Makefile
 create mode 100644 arch/riscv/kernel/probes/decode-insn.c
 create mode 100644 arch/riscv/kernel/probes/decode-insn.h
 create mode 100644 arch/riscv/kernel/probes/kprobes.c
 create mode 100644 arch/riscv/kernel/probes/kprobes_trampoline.S
 create mode 100644 arch/riscv/kernel/probes/simulate-insn.c
 create mode 100644 arch/riscv/kernel/probes/simulate-insn.h

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index b157ac82d486..11ef4030e8f2 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -44,6 +44,8 @@ config RISCV
 	select GENERIC_IRQ_MULTI_HANDLER
 	select ARCH_HAS_PTE_SPECIAL
 	select HAVE_REGS_AND_STACK_ACCESS_API
+	select HAVE_KPROBES
+	select HAVE_KRETPROBES
 
 config MMU
 	def_bool y
@@ -89,9 +91,6 @@ config PGTABLE_LEVELS
 	default 3 if 64BIT
 	default 2
 
-config HAVE_KPROBES
-	def_bool n
-
 menu "Platform type"
 
 choice
diff --git a/arch/riscv/include/asm/kprobes.h b/arch/riscv/include/asm/kprobes.h
index c7eb010d1528..657adcd35a3d 100644
--- a/arch/riscv/include/asm/kprobes.h
+++ b/arch/riscv/include/asm/kprobes.h
@@ -19,4 +19,34 @@
 
 #include <asm-generic/kprobes.h>
 
+#ifdef CONFIG_KPROBES
+#include <linux/types.h>
+#include <linux/ptrace.h>
+#include <linux/percpu.h>
+
+#define flush_insn_slot(p)		do { } while (0)
+#define kretprobe_blacklist_size	0
+
+#include <asm/probes.h>
+
+struct prev_kprobe {
+	struct kprobe *kp;
+	unsigned int status;
+};
+
+/* per-cpu kprobe control block */
+struct kprobe_ctlblk {
+	unsigned int kprobe_status;
+	struct prev_kprobe prev_kprobe;
+};
+
+void arch_remove_kprobe(struct kprobe *p);
+int kprobe_fault_handler(struct pt_regs *regs, unsigned int cause);
+int kprobe_exceptions_notify(struct notifier_block *self,
+			     unsigned long val, void *data);
+int kprobe_breakpoint_handler(struct pt_regs *regs);
+void kretprobe_trampoline(void);
+void __kprobes *trampoline_probe_handler(struct pt_regs *regs);
+
+#endif /* CONFIG_KPROBES */
 #endif /* _RISCV_KPROBES_H */
diff --git a/arch/riscv/include/asm/probes.h b/arch/riscv/include/asm/probes.h
new file mode 100644
index 000000000000..64cf12567539
--- /dev/null
+++ b/arch/riscv/include/asm/probes.h
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Based on arch/arm64/include/asm/probes.h
+ *
+ * Copyright (C) 2013 Linaro Limited
+ */
+#ifndef _RISCV_PROBES_H
+#define _RISCV_PROBES_H
+
+typedef u32 probe_opcode_t;
+typedef void (probes_handler_t) (u32 opcode, long addr, struct pt_regs *);
+
+/* architecture specific copy of original instruction */
+struct arch_probe_insn {
+	probes_handler_t *handler;
+	/* restore address after simulation */
+	unsigned long restore;
+};
+#ifdef CONFIG_KPROBES
+typedef u32 kprobe_opcode_t;
+struct arch_specific_insn {
+	struct arch_probe_insn api;
+};
+#endif
+
+#endif /* _RISCV_PROBES_H */
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index f13f7f276639..5360a445b9d3 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -28,6 +28,7 @@ obj-y	+= stacktrace.o
 obj-y	+= vdso.o
 obj-y	+= cacheinfo.o
 obj-y	+= vdso/
+obj-y	+= probes/
 
 CFLAGS_setup.o := -mcmodel=medany
 
diff --git a/arch/riscv/kernel/probes/Makefile b/arch/riscv/kernel/probes/Makefile
new file mode 100644
index 000000000000..144d1c1743fb
--- /dev/null
+++ b/arch/riscv/kernel/probes/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+obj-$(CONFIG_KPROBES)		+= kprobes.o kprobes_trampoline.o \
+				   decode-insn.o simulate-insn.o
diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c
new file mode 100644
index 000000000000..2d8f46f4c2e7
--- /dev/null
+++ b/arch/riscv/kernel/probes/decode-insn.c
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+#include <linux/kernel.h>
+#include <linux/kprobes.h>
+#include <linux/module.h>
+#include <linux/kallsyms.h>
+#include <asm/sections.h>
+
+#include "decode-insn.h"
+#include "simulate-insn.h"
+
+#define C_ADDISP16_MASK 0x6F83
+#define C_ADDISP16_VAL  0x6101
+
+/* Return:
+ *   INSN_REJECTED     If instruction is one not allowed to kprobe,
+ *   INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot.
+ */
+enum probe_insn __kprobes
+riscv_probe_decode_insn(kprobe_opcode_t *addr, struct arch_probe_insn *api)
+{
+	probe_opcode_t insn = le32_to_cpu(*addr);
+
+	if (!is_compressed_insn(insn)) {
+		pr_warn("Can't handle non-compressed instruction %x\n", insn);
+		return INSN_REJECTED;
+	}
+
+	/* c.addisp16 imm */
+	if ((insn & C_ADDISP16_MASK) == C_ADDISP16_VAL) {
+		api->handler = simulate_caddisp16;
+	} else {
+		pr_warn("Rejected unknown instruction %x\n", insn);
+		return INSN_REJECTED;
+	}
+
+	return INSN_GOOD_NO_SLOT;
+}
diff --git a/arch/riscv/kernel/probes/decode-insn.h b/arch/riscv/kernel/probes/decode-insn.h
new file mode 100644
index 000000000000..0053ed6a308a
--- /dev/null
+++ b/arch/riscv/kernel/probes/decode-insn.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+#ifndef _RISCV_KERNEL_KPROBES_DECODE_INSN_H
+#define _RISCV_KERNEL_KPROBES_DECODE_INSN_H
+
+#include <asm/sections.h>
+#include <asm/kprobes.h>
+
+enum probe_insn {
+	INSN_REJECTED,
+	INSN_GOOD_NO_SLOT,
+};
+
+/*
+ * Compressed instruction format:
+ * xxxxxxxxxxxxxxaa where aa != 11
+ */
+#define is_compressed_insn(insn) ((insn & 0x3) != 0x3)
+
+#ifdef CONFIG_KPROBES
+enum probe_insn __kprobes
+riscv_probe_decode_insn(kprobe_opcode_t *addr, struct arch_probe_insn *asi);
+#endif
+#endif /* _RISCV_KERNEL_KPROBES_DECODE_INSN_H */
diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
new file mode 100644
index 000000000000..3c7b5cf72ee1
--- /dev/null
+++ b/arch/riscv/kernel/probes/kprobes.c
@@ -0,0 +1,401 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+/*
+ * Kprobes support for RISC-V
+ *
+ * Author: Patrick St?hlin <me@packi.ch>
+ */
+#include <linux/kprobes.h>
+#include <linux/extable.h>
+#include <linux/slab.h>
+#include <asm/ptrace.h>
+#include <linux/uaccess.h>
+#include <asm/sections.h>
+
+#include "decode-insn.h"
+
+DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
+DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
+
+static void __kprobes
+post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
+
+static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
+{
+	if (is_compressed_insn(opcode))
+		*(u16 *)addr = cpu_to_le16(opcode);
+	else
+		*addr = cpu_to_le32(opcode);
+
+	return 0;
+}
+
+static void __kprobes arch_prepare_simulate(struct kprobe *p)
+{
+	unsigned long offset = is_compressed_insn(p->opcode) ? 2 : 4;
+
+	p->ainsn.api.restore = (unsigned long)p->addr + offset;
+}
+
+static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	if (p->ainsn.api.handler)
+		p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);
+
+	/* single instruction simulated, now go for post processing */
+	post_kprobe_handler(kcb, regs);
+}
+
+int __kprobes arch_prepare_kprobe(struct kprobe *p)
+{
+	unsigned long probe_addr = (unsigned long)p->addr;
+	extern char __start_rodata[];
+	extern char __end_rodata[];
+
+	if (probe_addr & 0x1) {
+		pr_warn("Address not aligned.\n");
+		return -EINVAL;
+	}
+
+	/* copy instruction */
+	p->opcode = le32_to_cpu(*p->addr);
+
+	if (probe_addr >= (unsigned long) __start_rodata &&
+	    probe_addr <= (unsigned long) __end_rodata) {
+		return -EINVAL;
+	}
+
+	/* decode instruction */
+	switch (riscv_probe_decode_insn(p->addr, &p->ainsn.api)) {
+	case INSN_REJECTED:	/* insn not supported */
+		return -EINVAL;
+
+	case INSN_GOOD_NO_SLOT:	/* insn needs simulation */
+		break;
+	}
+
+	arch_prepare_simulate(p);
+
+	return 0;
+}
+
+#define C_EBREAK_OPCODE 0x9002
+
+/* arm kprobe: install breakpoint in text */
+void __kprobes arch_arm_kprobe(struct kprobe *p)
+{
+	patch_text(p->addr, C_EBREAK_OPCODE);
+}
+
+/* disarm kprobe: remove breakpoint from text */
+void __kprobes arch_disarm_kprobe(struct kprobe *p)
+{
+	patch_text(p->addr, p->opcode);
+}
+
+void __kprobes arch_remove_kprobe(struct kprobe *p)
+{
+}
+
+static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
+{
+	kcb->prev_kprobe.kp = kprobe_running();
+	kcb->prev_kprobe.status = kcb->kprobe_status;
+}
+
+static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
+{
+	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
+	kcb->kprobe_status = kcb->prev_kprobe.status;
+}
+
+static void __kprobes set_current_kprobe(struct kprobe *p)
+{
+	__this_cpu_write(current_kprobe, p);
+}
+
+static void __kprobes simulate(struct kprobe *p,
+			       struct pt_regs *regs,
+			       struct kprobe_ctlblk *kcb, int reenter)
+{
+	if (reenter) {
+		save_previous_kprobe(kcb);
+		set_current_kprobe(p);
+		kcb->kprobe_status = KPROBE_REENTER;
+	} else {
+		kcb->kprobe_status = KPROBE_HIT_SS;
+	}
+
+	arch_simulate_insn(p, regs);
+}
+
+static int __kprobes reenter_kprobe(struct kprobe *p,
+				    struct pt_regs *regs,
+				    struct kprobe_ctlblk *kcb)
+{
+	switch (kcb->kprobe_status) {
+	case KPROBE_HIT_SSDONE:
+	case KPROBE_HIT_ACTIVE:
+		kprobes_inc_nmissed_count(p);
+		simulate(p, regs, kcb, 1);
+		break;
+	case KPROBE_HIT_SS:
+	case KPROBE_REENTER:
+		pr_warn("Unrecoverable kprobe detected.\n");
+		dump_kprobe(p);
+		BUG();
+		break;
+	default:
+		WARN_ON(1);
+		return 0;
+	}
+
+	return 1;
+}
+
+static void __kprobes
+post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
+{
+	struct kprobe *cur = kprobe_running();
+
+	if (!cur)
+		return;
+
+	/* return addr restore if non-branching insn */
+	if (cur->ainsn.api.restore != 0)
+		instruction_pointer_set(regs, cur->ainsn.api.restore);
+
+	/* restore back original saved kprobe variables and continue */
+	if (kcb->kprobe_status == KPROBE_REENTER) {
+		restore_previous_kprobe(kcb);
+		return;
+	}
+	/* call post handler */
+	kcb->kprobe_status = KPROBE_HIT_SSDONE;
+	if (cur->post_handler)	{
+		/* post_handler can hit breakpoint and single step
+		 * again, so we enable D-flag for recursive exception.
+		 */
+		cur->post_handler(cur, regs, 0);
+	}
+
+	reset_current_kprobe();
+}
+
+int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int cause)
+{
+	struct kprobe *cur = kprobe_running();
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	switch (kcb->kprobe_status) {
+	case KPROBE_HIT_SS:
+	case KPROBE_REENTER:
+		/*
+		 * We are here because the instruction being single
+		 * stepped caused a page fault. We reset the current
+		 * kprobe and the ip points back to the probe address
+		 * and allow the page fault handler to continue as a
+		 * normal page fault.
+		 */
+		instruction_pointer_set(regs, (unsigned long) cur->addr);
+		if (!instruction_pointer(regs))
+			BUG();
+
+		if (kcb->kprobe_status == KPROBE_REENTER)
+			restore_previous_kprobe(kcb);
+		else
+			reset_current_kprobe();
+
+		break;
+	case KPROBE_HIT_ACTIVE:
+	case KPROBE_HIT_SSDONE:
+		/*
+		 * We increment the nmissed count for accounting,
+		 * we can also use npre/npostfault count for accounting
+		 * these specific fault cases.
+		 */
+		kprobes_inc_nmissed_count(cur);
+
+		/*
+		 * We come here because instructions in the pre/post
+		 * handler caused the page_fault, this could happen
+		 * if handler tries to access user space by
+		 * copy_from_user(), get_user() etc. Let the
+		 * user-specified handler try to fix it first.
+		 */
+		if (cur->fault_handler && cur->fault_handler(cur, regs, cause))
+			return 1;
+
+		/*
+		 * In case the user-specified fault handler returned
+		 * zero, try to fix up.
+		 */
+		if (fixup_exception(regs))
+			return 1;
+	}
+	return 0;
+}
+
+static void __kprobes kprobe_handler(struct pt_regs *regs)
+{
+	struct kprobe *p, *cur_kprobe;
+	struct kprobe_ctlblk *kcb;
+	unsigned long addr = instruction_pointer(regs);
+
+	kcb = get_kprobe_ctlblk();
+	cur_kprobe = kprobe_running();
+
+	p = get_kprobe((kprobe_opcode_t *) addr);
+
+	if (p) {
+		if (cur_kprobe) {
+			if (reenter_kprobe(p, regs, kcb))
+				return;
+		} else {
+			/* Probe hit */
+			set_current_kprobe(p);
+			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
+
+			/*
+			 * If we have no pre-handler or it returned 0, we
+			 * continue with normal processing.  If we have a
+			 * pre-handler and it returned non-zero, it will
+			 * modify the execution path and no need to single
+			 * stepping. Let's just reset current kprobe and exit.
+			 *
+			 * pre_handler can hit a breakpoint and can step thru
+			 * before return, keep PSTATE D-flag enabled until
+			 * pre_handler return back.
+			 */
+			if (!p->pre_handler || !p->pre_handler(p, regs))
+				simulate(p, regs, kcb, 0);
+			else
+				reset_current_kprobe();
+		}
+	}
+	/*
+	 * The breakpoint instruction was removed right
+	 * after we hit it.  Another cpu has removed
+	 * either a probepoint or a debugger breakpoint
+	 * at this address.  In either case, no further
+	 * handling of this interrupt is appropriate.
+	 * Return back to original instruction, and continue.
+	 */
+}
+
+int __kprobes
+kprobe_breakpoint_handler(struct pt_regs *regs)
+{
+	kprobe_handler(regs);
+	return 1;
+}
+
+bool arch_within_kprobe_blacklist(unsigned long addr)
+{
+	if ((addr >= (unsigned long)__kprobes_text_start &&
+	    addr < (unsigned long)__kprobes_text_end) ||
+	    (addr >= (unsigned long)__entry_text_start &&
+	    addr < (unsigned long)__entry_text_end) ||
+	    !!search_exception_tables(addr))
+		return true;
+
+	return false;
+}
+
+void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
+{
+	struct kretprobe_instance *ri = NULL;
+	struct hlist_head *head, empty_rp;
+	struct hlist_node *tmp;
+	unsigned long flags, orig_ret_address = 0;
+	unsigned long trampoline_address =
+		(unsigned long)&kretprobe_trampoline;
+	kprobe_opcode_t *correct_ret_addr = NULL;
+
+	INIT_HLIST_HEAD(&empty_rp);
+	kretprobe_hash_lock(current, &head, &flags);
+
+	/*
+	 * It is possible to have multiple instances associated with a given
+	 * task either because multiple functions in the call path have
+	 * return probes installed on them, and/or more than one
+	 * return probe was registered for a target function.
+	 *
+	 * We can handle this because:
+	 *     - instances are always pushed into the head of the list
+	 *     - when multiple return probes are registered for the same
+	 *	 function, the (chronologically) first instance's ret_addr
+	 *	 will be the real return address, and all the rest will
+	 *	 point to kretprobe_trampoline.
+	 */
+	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
+		if (ri->task != current)
+			/* another task is sharing our hash bucket */
+			continue;
+
+		orig_ret_address = (unsigned long)ri->ret_addr;
+
+		if (orig_ret_address != trampoline_address)
+			/*
+			 * This is the real return address. Any other
+			 * instances associated with this task are for
+			 * other calls deeper on the call stack
+			 */
+			break;
+	}
+
+	kretprobe_assert(ri, orig_ret_address, trampoline_address);
+
+	correct_ret_addr = ri->ret_addr;
+	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
+		if (ri->task != current)
+			/* another task is sharing our hash bucket */
+			continue;
+
+		orig_ret_address = (unsigned long)ri->ret_addr;
+		if (ri->rp && ri->rp->handler) {
+			__this_cpu_write(current_kprobe, &ri->rp->kp);
+			get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
+			ri->ret_addr = correct_ret_addr;
+			ri->rp->handler(ri, regs);
+			__this_cpu_write(current_kprobe, NULL);
+		}
+
+		recycle_rp_inst(ri, &empty_rp);
+
+		if (orig_ret_address != trampoline_address)
+			/*
+			 * This is the real return address. Any other
+			 * instances associated with this task are for
+			 * other calls deeper on the call stack
+			 */
+			break;
+	}
+
+	kretprobe_hash_unlock(current, &flags);
+
+	hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
+		hlist_del(&ri->hlist);
+		kfree(ri);
+	}
+	return (void *)orig_ret_address;
+}
+
+void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
+				      struct pt_regs *regs)
+{
+	ri->ret_addr = (kprobe_opcode_t *)regs->ra;
+	regs->ra = (long)&kretprobe_trampoline;
+}
+
+int __kprobes arch_trampoline_kprobe(struct kprobe *p)
+{
+	return 0;
+}
+
+int __init arch_init_kprobes(void)
+{
+	return 0;
+}
diff --git a/arch/riscv/kernel/probes/kprobes_trampoline.S b/arch/riscv/kernel/probes/kprobes_trampoline.S
new file mode 100644
index 000000000000..c7ceda9556a3
--- /dev/null
+++ b/arch/riscv/kernel/probes/kprobes_trampoline.S
@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+
+#include <linux/linkage.h>
+
+#include <asm/asm.h>
+#include <asm/asm-offsets.h>
+
+	.text
+	.altmacro
+
+	.macro save_all_base_regs
+	REG_S x1,  PT_RA(sp)
+	REG_S x3,  PT_GP(sp)
+	REG_S x4,  PT_TP(sp)
+	REG_S x5,  PT_T0(sp)
+	REG_S x6,  PT_T1(sp)
+	REG_S x7,  PT_T2(sp)
+	REG_S x8,  PT_S0(sp)
+	REG_S x9,  PT_S1(sp)
+	REG_S x10, PT_A0(sp)
+	REG_S x11, PT_A1(sp)
+	REG_S x12, PT_A2(sp)
+	REG_S x13, PT_A3(sp)
+	REG_S x14, PT_A4(sp)
+	REG_S x15, PT_A5(sp)
+	REG_S x16, PT_A6(sp)
+	REG_S x17, PT_A7(sp)
+	REG_S x18, PT_S2(sp)
+	REG_S x19, PT_S3(sp)
+	REG_S x20, PT_S4(sp)
+	REG_S x21, PT_S5(sp)
+	REG_S x22, PT_S6(sp)
+	REG_S x23, PT_S7(sp)
+	REG_S x24, PT_S8(sp)
+	REG_S x25, PT_S9(sp)
+	REG_S x26, PT_S10(sp)
+	REG_S x27, PT_S11(sp)
+	REG_S x28, PT_T3(sp)
+	REG_S x29, PT_T4(sp)
+	REG_S x30, PT_T5(sp)
+	REG_S x31, PT_T6(sp)
+	.endm
+
+	.macro restore_all_base_regs
+	REG_L x3,  PT_GP(sp)
+	REG_L x4,  PT_TP(sp)
+	REG_L x5,  PT_T0(sp)
+	REG_L x6,  PT_T1(sp)
+	REG_L x7,  PT_T2(sp)
+	REG_L x8,  PT_S0(sp)
+	REG_L x9,  PT_S1(sp)
+	REG_L x10, PT_A0(sp)
+	REG_L x11, PT_A1(sp)
+	REG_L x12, PT_A2(sp)
+	REG_L x13, PT_A3(sp)
+	REG_L x14, PT_A4(sp)
+	REG_L x15, PT_A5(sp)
+	REG_L x16, PT_A6(sp)
+	REG_L x17, PT_A7(sp)
+	REG_L x18, PT_S2(sp)
+	REG_L x19, PT_S3(sp)
+	REG_L x20, PT_S4(sp)
+	REG_L x21, PT_S5(sp)
+	REG_L x22, PT_S6(sp)
+	REG_L x23, PT_S7(sp)
+	REG_L x24, PT_S8(sp)
+	REG_L x25, PT_S9(sp)
+	REG_L x26, PT_S10(sp)
+	REG_L x27, PT_S11(sp)
+	REG_L x28, PT_T3(sp)
+	REG_L x29, PT_T4(sp)
+	REG_L x30, PT_T5(sp)
+	REG_L x31, PT_T6(sp)
+	.endm
+
+ENTRY(kretprobe_trampoline)
+	addi sp, sp, -(PT_SIZE_ON_STACK)
+	save_all_base_regs
+
+	move a0, sp /* pt_regs */
+
+	call trampoline_probe_handler
+
+	/* use the result as the return-address */
+	move ra, a0
+
+	restore_all_base_regs
+	addi sp, sp, PT_SIZE_ON_STACK
+
+	ret
+ENDPROC(kretprobe_trampoline)
diff --git a/arch/riscv/kernel/probes/simulate-insn.c b/arch/riscv/kernel/probes/simulate-insn.c
new file mode 100644
index 000000000000..5734d9bae22f
--- /dev/null
+++ b/arch/riscv/kernel/probes/simulate-insn.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+#include <linux/bitops.h>
+#include <linux/kernel.h>
+#include <linux/kprobes.h>
+
+#include "simulate-insn.h"
+
+#define bit_at(value, bit)		((value) & (1 << (bit)))
+#define move_bit_at(value, bit, to)	((bit_at(value, bit) >> bit) << to)
+
+void __kprobes
+simulate_caddisp16(u32 opcode, long addr, struct pt_regs *regs)
+{
+	s16 imm;
+
+	/*
+	 * Immediate value layout in c.addisp16:
+	 * xxx9 xxxx x468 75xx
+	 * 1  1    8    4    0
+	 * 5  2
+	 */
+	imm = sign_extend32(
+		move_bit_at(opcode, 12, 9) |
+		move_bit_at(opcode, 6, 4) |
+		move_bit_at(opcode, 5, 6) |
+		move_bit_at(opcode, 4, 8) |
+		move_bit_at(opcode, 3, 7) |
+		move_bit_at(opcode, 2, 5),
+		9);
+
+	regs->sp += imm;
+}
diff --git a/arch/riscv/kernel/probes/simulate-insn.h b/arch/riscv/kernel/probes/simulate-insn.h
new file mode 100644
index 000000000000..dc2c06c30167
--- /dev/null
+++ b/arch/riscv/kernel/probes/simulate-insn.h
@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+
+#ifndef _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H
+#define _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H
+
+void simulate_caddisp16(u32 opcode, long addr, struct pt_regs *regs);
+
+#endif /* _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H */
diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index 24a9333dda2c..d7113178d401 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -18,6 +18,7 @@
 #include <linux/sched/signal.h>
 #include <linux/signal.h>
 #include <linux/kdebug.h>
+#include <linux/kprobes.h>
 #include <linux/uaccess.h>
 #include <linux/mm.h>
 #include <linux/module.h>
@@ -120,8 +121,14 @@ DO_ERROR_INFO(do_trap_ecall_m,
 
 asmlinkage void do_trap_break(struct pt_regs *regs)
 {
+	bool handler_found = false;
+
+#ifdef CONFIG_KPROBES
+	if (kprobe_breakpoint_handler(regs))
+		handler_found = 1;
+#endif
 #ifdef CONFIG_GENERIC_BUG
-	if (!user_mode(regs)) {
+	if (!handler_found && !user_mode(regs)) {
 		enum bug_trap_type type;
 
 		type = report_bug(regs->sepc, regs);
@@ -137,7 +144,9 @@ asmlinkage void do_trap_break(struct pt_regs *regs)
 	}
 #endif /* CONFIG_GENERIC_BUG */
 
-	force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)(regs->sepc), current);
+	if (!handler_found)
+		force_sig_fault(SIGTRAP, TRAP_BRKPT,
+			(void __user *)(regs->sepc), current);
 }
 
 #ifdef CONFIG_GENERIC_BUG
diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index 88401d5125bc..eff816e33479 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -22,6 +22,7 @@
 
 #include <linux/mm.h>
 #include <linux/kernel.h>
+#include <linux/kprobes.h>
 #include <linux/interrupt.h>
 #include <linux/perf_event.h>
 #include <linux/signal.h>
@@ -30,11 +31,33 @@
 #include <asm/pgalloc.h>
 #include <asm/ptrace.h>
 
+#ifdef CONFIG_KPROBES
+static inline int notify_page_fault(struct pt_regs *regs, unsigned int cause)
+{
+	int ret = 0;
+
+	/* kprobe_running() needs smp_processor_id() */
+	if (!user_mode(regs)) {
+		preempt_disable();
+		if (kprobe_running() && kprobe_fault_handler(regs, cause))
+			ret = 1;
+		preempt_enable();
+	}
+
+	return ret;
+}
+#else
+static inline int notify_page_fault(struct pt_regs *regs, unsigned int cause)
+{
+	return 0;
+}
+#endif
+
 /*
  * This routine handles page faults.  It determines the address and the
  * problem, and then passes it off to one of the appropriate routines.
  */
-asmlinkage void do_page_fault(struct pt_regs *regs)
+asmlinkage void __kprobes do_page_fault(struct pt_regs *regs)
 {
 	struct task_struct *tsk;
 	struct vm_area_struct *vma;
@@ -47,6 +70,9 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 	cause = regs->scause;
 	addr = regs->sbadaddr;
 
+	if (notify_page_fault(regs, cause))
+		return;
+
 	tsk = current;
 	mm = tsk->mm;
 
-- 
2.17.1

^ permalink raw reply	[flat|nested] 18+ messages in thread

* [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support
  2018-11-13 19:58 ` [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support me
@ 2018-11-13 19:58   ` Patrick Stählin
  2018-11-14  8:37   ` mhiramat
  1 sibling, 0 replies; 18+ messages in thread
From: Patrick Stählin @ 2018-11-13 19:58 UTC (permalink / raw)
  To: linux-riscv
  Cc: Patrick Stählin, Albert Ou, Anders Roxell, Andrew Morton,
	Alan Kao, Catalin Marinas, Palmer Dabbelt, Will Deacon,
	linux-kernel, Al Viro, Souptick Joarder, Zong Li,
	Masami Hiramatsu, Thomas Gleixner, Jim Wilson, zhong jiang,
	Ingo Molnar, Luc Van Oostenryck, Eric W. Biederman

First implementation, adapted from arm64. The C.ADDISP16 instruction
gets simulated and the kprobes-handler called by inserting a C.EBREAK
instruction.

C.ADDISP16 was chosen as it sets-up the stack frame for functions.
Some work has been done to support probes on non-compressed
instructions but there is no support yet for decoding those.

The way forward should be to uncompress the instructions for simulation
to reduce the number of instructions used to decode the immediate
values on probe hit.

Signed-off-by: Patrick Stählin <me@packi.ch>
---
 arch/riscv/Kconfig                            |   5 +-
 arch/riscv/include/asm/kprobes.h              |  30 ++
 arch/riscv/include/asm/probes.h               |  26 ++
 arch/riscv/kernel/Makefile                    |   1 +
 arch/riscv/kernel/probes/Makefile             |   3 +
 arch/riscv/kernel/probes/decode-insn.c        |  38 ++
 arch/riscv/kernel/probes/decode-insn.h        |  23 +
 arch/riscv/kernel/probes/kprobes.c            | 401 ++++++++++++++++++
 arch/riscv/kernel/probes/kprobes_trampoline.S |  91 ++++
 arch/riscv/kernel/probes/simulate-insn.c      |  33 ++
 arch/riscv/kernel/probes/simulate-insn.h      |   8 +
 arch/riscv/kernel/traps.c                     |  13 +-
 arch/riscv/mm/fault.c                         |  28 +-
 13 files changed, 694 insertions(+), 6 deletions(-)
 create mode 100644 arch/riscv/include/asm/probes.h
 create mode 100644 arch/riscv/kernel/probes/Makefile
 create mode 100644 arch/riscv/kernel/probes/decode-insn.c
 create mode 100644 arch/riscv/kernel/probes/decode-insn.h
 create mode 100644 arch/riscv/kernel/probes/kprobes.c
 create mode 100644 arch/riscv/kernel/probes/kprobes_trampoline.S
 create mode 100644 arch/riscv/kernel/probes/simulate-insn.c
 create mode 100644 arch/riscv/kernel/probes/simulate-insn.h

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index b157ac82d486..11ef4030e8f2 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -44,6 +44,8 @@ config RISCV
 	select GENERIC_IRQ_MULTI_HANDLER
 	select ARCH_HAS_PTE_SPECIAL
 	select HAVE_REGS_AND_STACK_ACCESS_API
+	select HAVE_KPROBES
+	select HAVE_KRETPROBES
 
 config MMU
 	def_bool y
@@ -89,9 +91,6 @@ config PGTABLE_LEVELS
 	default 3 if 64BIT
 	default 2
 
-config HAVE_KPROBES
-	def_bool n
-
 menu "Platform type"
 
 choice
diff --git a/arch/riscv/include/asm/kprobes.h b/arch/riscv/include/asm/kprobes.h
index c7eb010d1528..657adcd35a3d 100644
--- a/arch/riscv/include/asm/kprobes.h
+++ b/arch/riscv/include/asm/kprobes.h
@@ -19,4 +19,34 @@
 
 #include <asm-generic/kprobes.h>
 
+#ifdef CONFIG_KPROBES
+#include <linux/types.h>
+#include <linux/ptrace.h>
+#include <linux/percpu.h>
+
+#define flush_insn_slot(p)		do { } while (0)
+#define kretprobe_blacklist_size	0
+
+#include <asm/probes.h>
+
+struct prev_kprobe {
+	struct kprobe *kp;
+	unsigned int status;
+};
+
+/* per-cpu kprobe control block */
+struct kprobe_ctlblk {
+	unsigned int kprobe_status;
+	struct prev_kprobe prev_kprobe;
+};
+
+void arch_remove_kprobe(struct kprobe *p);
+int kprobe_fault_handler(struct pt_regs *regs, unsigned int cause);
+int kprobe_exceptions_notify(struct notifier_block *self,
+			     unsigned long val, void *data);
+int kprobe_breakpoint_handler(struct pt_regs *regs);
+void kretprobe_trampoline(void);
+void __kprobes *trampoline_probe_handler(struct pt_regs *regs);
+
+#endif /* CONFIG_KPROBES */
 #endif /* _RISCV_KPROBES_H */
diff --git a/arch/riscv/include/asm/probes.h b/arch/riscv/include/asm/probes.h
new file mode 100644
index 000000000000..64cf12567539
--- /dev/null
+++ b/arch/riscv/include/asm/probes.h
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Based on arch/arm64/include/asm/probes.h
+ *
+ * Copyright (C) 2013 Linaro Limited
+ */
+#ifndef _RISCV_PROBES_H
+#define _RISCV_PROBES_H
+
+typedef u32 probe_opcode_t;
+typedef void (probes_handler_t) (u32 opcode, long addr, struct pt_regs *);
+
+/* architecture specific copy of original instruction */
+struct arch_probe_insn {
+	probes_handler_t *handler;
+	/* restore address after simulation */
+	unsigned long restore;
+};
+#ifdef CONFIG_KPROBES
+typedef u32 kprobe_opcode_t;
+struct arch_specific_insn {
+	struct arch_probe_insn api;
+};
+#endif
+
+#endif /* _RISCV_PROBES_H */
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index f13f7f276639..5360a445b9d3 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -28,6 +28,7 @@ obj-y	+= stacktrace.o
 obj-y	+= vdso.o
 obj-y	+= cacheinfo.o
 obj-y	+= vdso/
+obj-y	+= probes/
 
 CFLAGS_setup.o := -mcmodel=medany
 
diff --git a/arch/riscv/kernel/probes/Makefile b/arch/riscv/kernel/probes/Makefile
new file mode 100644
index 000000000000..144d1c1743fb
--- /dev/null
+++ b/arch/riscv/kernel/probes/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+obj-$(CONFIG_KPROBES)		+= kprobes.o kprobes_trampoline.o \
+				   decode-insn.o simulate-insn.o
diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c
new file mode 100644
index 000000000000..2d8f46f4c2e7
--- /dev/null
+++ b/arch/riscv/kernel/probes/decode-insn.c
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+#include <linux/kernel.h>
+#include <linux/kprobes.h>
+#include <linux/module.h>
+#include <linux/kallsyms.h>
+#include <asm/sections.h>
+
+#include "decode-insn.h"
+#include "simulate-insn.h"
+
+#define C_ADDISP16_MASK 0x6F83
+#define C_ADDISP16_VAL  0x6101
+
+/* Return:
+ *   INSN_REJECTED     If instruction is one not allowed to kprobe,
+ *   INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot.
+ */
+enum probe_insn __kprobes
+riscv_probe_decode_insn(kprobe_opcode_t *addr, struct arch_probe_insn *api)
+{
+	probe_opcode_t insn = le32_to_cpu(*addr);
+
+	if (!is_compressed_insn(insn)) {
+		pr_warn("Can't handle non-compressed instruction %x\n", insn);
+		return INSN_REJECTED;
+	}
+
+	/* c.addisp16 imm */
+	if ((insn & C_ADDISP16_MASK) == C_ADDISP16_VAL) {
+		api->handler = simulate_caddisp16;
+	} else {
+		pr_warn("Rejected unknown instruction %x\n", insn);
+		return INSN_REJECTED;
+	}
+
+	return INSN_GOOD_NO_SLOT;
+}
diff --git a/arch/riscv/kernel/probes/decode-insn.h b/arch/riscv/kernel/probes/decode-insn.h
new file mode 100644
index 000000000000..0053ed6a308a
--- /dev/null
+++ b/arch/riscv/kernel/probes/decode-insn.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+#ifndef _RISCV_KERNEL_KPROBES_DECODE_INSN_H
+#define _RISCV_KERNEL_KPROBES_DECODE_INSN_H
+
+#include <asm/sections.h>
+#include <asm/kprobes.h>
+
+enum probe_insn {
+	INSN_REJECTED,
+	INSN_GOOD_NO_SLOT,
+};
+
+/*
+ * Compressed instruction format:
+ * xxxxxxxxxxxxxxaa where aa != 11
+ */
+#define is_compressed_insn(insn) ((insn & 0x3) != 0x3)
+
+#ifdef CONFIG_KPROBES
+enum probe_insn __kprobes
+riscv_probe_decode_insn(kprobe_opcode_t *addr, struct arch_probe_insn *asi);
+#endif
+#endif /* _RISCV_KERNEL_KPROBES_DECODE_INSN_H */
diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
new file mode 100644
index 000000000000..3c7b5cf72ee1
--- /dev/null
+++ b/arch/riscv/kernel/probes/kprobes.c
@@ -0,0 +1,401 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+/*
+ * Kprobes support for RISC-V
+ *
+ * Author: Patrick Stählin <me@packi.ch>
+ */
+#include <linux/kprobes.h>
+#include <linux/extable.h>
+#include <linux/slab.h>
+#include <asm/ptrace.h>
+#include <linux/uaccess.h>
+#include <asm/sections.h>
+
+#include "decode-insn.h"
+
+DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
+DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
+
+static void __kprobes
+post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
+
+static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
+{
+	if (is_compressed_insn(opcode))
+		*(u16 *)addr = cpu_to_le16(opcode);
+	else
+		*addr = cpu_to_le32(opcode);
+
+	return 0;
+}
+
+static void __kprobes arch_prepare_simulate(struct kprobe *p)
+{
+	unsigned long offset = is_compressed_insn(p->opcode) ? 2 : 4;
+
+	p->ainsn.api.restore = (unsigned long)p->addr + offset;
+}
+
+static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	if (p->ainsn.api.handler)
+		p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);
+
+	/* single instruction simulated, now go for post processing */
+	post_kprobe_handler(kcb, regs);
+}
+
+int __kprobes arch_prepare_kprobe(struct kprobe *p)
+{
+	unsigned long probe_addr = (unsigned long)p->addr;
+	extern char __start_rodata[];
+	extern char __end_rodata[];
+
+	if (probe_addr & 0x1) {
+		pr_warn("Address not aligned.\n");
+		return -EINVAL;
+	}
+
+	/* copy instruction */
+	p->opcode = le32_to_cpu(*p->addr);
+
+	if (probe_addr >= (unsigned long) __start_rodata &&
+	    probe_addr <= (unsigned long) __end_rodata) {
+		return -EINVAL;
+	}
+
+	/* decode instruction */
+	switch (riscv_probe_decode_insn(p->addr, &p->ainsn.api)) {
+	case INSN_REJECTED:	/* insn not supported */
+		return -EINVAL;
+
+	case INSN_GOOD_NO_SLOT:	/* insn needs simulation */
+		break;
+	}
+
+	arch_prepare_simulate(p);
+
+	return 0;
+}
+
+#define C_EBREAK_OPCODE 0x9002
+
+/* arm kprobe: install breakpoint in text */
+void __kprobes arch_arm_kprobe(struct kprobe *p)
+{
+	patch_text(p->addr, C_EBREAK_OPCODE);
+}
+
+/* disarm kprobe: remove breakpoint from text */
+void __kprobes arch_disarm_kprobe(struct kprobe *p)
+{
+	patch_text(p->addr, p->opcode);
+}
+
+void __kprobes arch_remove_kprobe(struct kprobe *p)
+{
+}
+
+static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
+{
+	kcb->prev_kprobe.kp = kprobe_running();
+	kcb->prev_kprobe.status = kcb->kprobe_status;
+}
+
+static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
+{
+	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
+	kcb->kprobe_status = kcb->prev_kprobe.status;
+}
+
+static void __kprobes set_current_kprobe(struct kprobe *p)
+{
+	__this_cpu_write(current_kprobe, p);
+}
+
+static void __kprobes simulate(struct kprobe *p,
+			       struct pt_regs *regs,
+			       struct kprobe_ctlblk *kcb, int reenter)
+{
+	if (reenter) {
+		save_previous_kprobe(kcb);
+		set_current_kprobe(p);
+		kcb->kprobe_status = KPROBE_REENTER;
+	} else {
+		kcb->kprobe_status = KPROBE_HIT_SS;
+	}
+
+	arch_simulate_insn(p, regs);
+}
+
+static int __kprobes reenter_kprobe(struct kprobe *p,
+				    struct pt_regs *regs,
+				    struct kprobe_ctlblk *kcb)
+{
+	switch (kcb->kprobe_status) {
+	case KPROBE_HIT_SSDONE:
+	case KPROBE_HIT_ACTIVE:
+		kprobes_inc_nmissed_count(p);
+		simulate(p, regs, kcb, 1);
+		break;
+	case KPROBE_HIT_SS:
+	case KPROBE_REENTER:
+		pr_warn("Unrecoverable kprobe detected.\n");
+		dump_kprobe(p);
+		BUG();
+		break;
+	default:
+		WARN_ON(1);
+		return 0;
+	}
+
+	return 1;
+}
+
+static void __kprobes
+post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
+{
+	struct kprobe *cur = kprobe_running();
+
+	if (!cur)
+		return;
+
+	/* return addr restore if non-branching insn */
+	if (cur->ainsn.api.restore != 0)
+		instruction_pointer_set(regs, cur->ainsn.api.restore);
+
+	/* restore back original saved kprobe variables and continue */
+	if (kcb->kprobe_status == KPROBE_REENTER) {
+		restore_previous_kprobe(kcb);
+		return;
+	}
+	/* call post handler */
+	kcb->kprobe_status = KPROBE_HIT_SSDONE;
+	if (cur->post_handler)	{
+		/* post_handler can hit breakpoint and single step
+		 * again, so we enable D-flag for recursive exception.
+		 */
+		cur->post_handler(cur, regs, 0);
+	}
+
+	reset_current_kprobe();
+}
+
+int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int cause)
+{
+	struct kprobe *cur = kprobe_running();
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	switch (kcb->kprobe_status) {
+	case KPROBE_HIT_SS:
+	case KPROBE_REENTER:
+		/*
+		 * We are here because the instruction being single
+		 * stepped caused a page fault. We reset the current
+		 * kprobe and the ip points back to the probe address
+		 * and allow the page fault handler to continue as a
+		 * normal page fault.
+		 */
+		instruction_pointer_set(regs, (unsigned long) cur->addr);
+		if (!instruction_pointer(regs))
+			BUG();
+
+		if (kcb->kprobe_status == KPROBE_REENTER)
+			restore_previous_kprobe(kcb);
+		else
+			reset_current_kprobe();
+
+		break;
+	case KPROBE_HIT_ACTIVE:
+	case KPROBE_HIT_SSDONE:
+		/*
+		 * We increment the nmissed count for accounting,
+		 * we can also use npre/npostfault count for accounting
+		 * these specific fault cases.
+		 */
+		kprobes_inc_nmissed_count(cur);
+
+		/*
+		 * We come here because instructions in the pre/post
+		 * handler caused the page_fault, this could happen
+		 * if handler tries to access user space by
+		 * copy_from_user(), get_user() etc. Let the
+		 * user-specified handler try to fix it first.
+		 */
+		if (cur->fault_handler && cur->fault_handler(cur, regs, cause))
+			return 1;
+
+		/*
+		 * In case the user-specified fault handler returned
+		 * zero, try to fix up.
+		 */
+		if (fixup_exception(regs))
+			return 1;
+	}
+	return 0;
+}
+
+static void __kprobes kprobe_handler(struct pt_regs *regs)
+{
+	struct kprobe *p, *cur_kprobe;
+	struct kprobe_ctlblk *kcb;
+	unsigned long addr = instruction_pointer(regs);
+
+	kcb = get_kprobe_ctlblk();
+	cur_kprobe = kprobe_running();
+
+	p = get_kprobe((kprobe_opcode_t *) addr);
+
+	if (p) {
+		if (cur_kprobe) {
+			if (reenter_kprobe(p, regs, kcb))
+				return;
+		} else {
+			/* Probe hit */
+			set_current_kprobe(p);
+			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
+
+			/*
+			 * If we have no pre-handler or it returned 0, we
+			 * continue with normal processing.  If we have a
+			 * pre-handler and it returned non-zero, it will
+			 * modify the execution path and no need to single
+			 * stepping. Let's just reset current kprobe and exit.
+			 *
+			 * pre_handler can hit a breakpoint and can step thru
+			 * before return, keep PSTATE D-flag enabled until
+			 * pre_handler return back.
+			 */
+			if (!p->pre_handler || !p->pre_handler(p, regs))
+				simulate(p, regs, kcb, 0);
+			else
+				reset_current_kprobe();
+		}
+	}
+	/*
+	 * The breakpoint instruction was removed right
+	 * after we hit it.  Another cpu has removed
+	 * either a probepoint or a debugger breakpoint
+	 * at this address.  In either case, no further
+	 * handling of this interrupt is appropriate.
+	 * Return back to original instruction, and continue.
+	 */
+}
+
+int __kprobes
+kprobe_breakpoint_handler(struct pt_regs *regs)
+{
+	kprobe_handler(regs);
+	return 1;
+}
+
+bool arch_within_kprobe_blacklist(unsigned long addr)
+{
+	if ((addr >= (unsigned long)__kprobes_text_start &&
+	    addr < (unsigned long)__kprobes_text_end) ||
+	    (addr >= (unsigned long)__entry_text_start &&
+	    addr < (unsigned long)__entry_text_end) ||
+	    !!search_exception_tables(addr))
+		return true;
+
+	return false;
+}
+
+void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
+{
+	struct kretprobe_instance *ri = NULL;
+	struct hlist_head *head, empty_rp;
+	struct hlist_node *tmp;
+	unsigned long flags, orig_ret_address = 0;
+	unsigned long trampoline_address =
+		(unsigned long)&kretprobe_trampoline;
+	kprobe_opcode_t *correct_ret_addr = NULL;
+
+	INIT_HLIST_HEAD(&empty_rp);
+	kretprobe_hash_lock(current, &head, &flags);
+
+	/*
+	 * It is possible to have multiple instances associated with a given
+	 * task either because multiple functions in the call path have
+	 * return probes installed on them, and/or more than one
+	 * return probe was registered for a target function.
+	 *
+	 * We can handle this because:
+	 *     - instances are always pushed into the head of the list
+	 *     - when multiple return probes are registered for the same
+	 *	 function, the (chronologically) first instance's ret_addr
+	 *	 will be the real return address, and all the rest will
+	 *	 point to kretprobe_trampoline.
+	 */
+	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
+		if (ri->task != current)
+			/* another task is sharing our hash bucket */
+			continue;
+
+		orig_ret_address = (unsigned long)ri->ret_addr;
+
+		if (orig_ret_address != trampoline_address)
+			/*
+			 * This is the real return address. Any other
+			 * instances associated with this task are for
+			 * other calls deeper on the call stack
+			 */
+			break;
+	}
+
+	kretprobe_assert(ri, orig_ret_address, trampoline_address);
+
+	correct_ret_addr = ri->ret_addr;
+	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
+		if (ri->task != current)
+			/* another task is sharing our hash bucket */
+			continue;
+
+		orig_ret_address = (unsigned long)ri->ret_addr;
+		if (ri->rp && ri->rp->handler) {
+			__this_cpu_write(current_kprobe, &ri->rp->kp);
+			get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
+			ri->ret_addr = correct_ret_addr;
+			ri->rp->handler(ri, regs);
+			__this_cpu_write(current_kprobe, NULL);
+		}
+
+		recycle_rp_inst(ri, &empty_rp);
+
+		if (orig_ret_address != trampoline_address)
+			/*
+			 * This is the real return address. Any other
+			 * instances associated with this task are for
+			 * other calls deeper on the call stack
+			 */
+			break;
+	}
+
+	kretprobe_hash_unlock(current, &flags);
+
+	hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
+		hlist_del(&ri->hlist);
+		kfree(ri);
+	}
+	return (void *)orig_ret_address;
+}
+
+void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
+				      struct pt_regs *regs)
+{
+	ri->ret_addr = (kprobe_opcode_t *)regs->ra;
+	regs->ra = (long)&kretprobe_trampoline;
+}
+
+int __kprobes arch_trampoline_kprobe(struct kprobe *p)
+{
+	return 0;
+}
+
+int __init arch_init_kprobes(void)
+{
+	return 0;
+}
diff --git a/arch/riscv/kernel/probes/kprobes_trampoline.S b/arch/riscv/kernel/probes/kprobes_trampoline.S
new file mode 100644
index 000000000000..c7ceda9556a3
--- /dev/null
+++ b/arch/riscv/kernel/probes/kprobes_trampoline.S
@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+
+#include <linux/linkage.h>
+
+#include <asm/asm.h>
+#include <asm/asm-offsets.h>
+
+	.text
+	.altmacro
+
+	.macro save_all_base_regs
+	REG_S x1,  PT_RA(sp)
+	REG_S x3,  PT_GP(sp)
+	REG_S x4,  PT_TP(sp)
+	REG_S x5,  PT_T0(sp)
+	REG_S x6,  PT_T1(sp)
+	REG_S x7,  PT_T2(sp)
+	REG_S x8,  PT_S0(sp)
+	REG_S x9,  PT_S1(sp)
+	REG_S x10, PT_A0(sp)
+	REG_S x11, PT_A1(sp)
+	REG_S x12, PT_A2(sp)
+	REG_S x13, PT_A3(sp)
+	REG_S x14, PT_A4(sp)
+	REG_S x15, PT_A5(sp)
+	REG_S x16, PT_A6(sp)
+	REG_S x17, PT_A7(sp)
+	REG_S x18, PT_S2(sp)
+	REG_S x19, PT_S3(sp)
+	REG_S x20, PT_S4(sp)
+	REG_S x21, PT_S5(sp)
+	REG_S x22, PT_S6(sp)
+	REG_S x23, PT_S7(sp)
+	REG_S x24, PT_S8(sp)
+	REG_S x25, PT_S9(sp)
+	REG_S x26, PT_S10(sp)
+	REG_S x27, PT_S11(sp)
+	REG_S x28, PT_T3(sp)
+	REG_S x29, PT_T4(sp)
+	REG_S x30, PT_T5(sp)
+	REG_S x31, PT_T6(sp)
+	.endm
+
+	.macro restore_all_base_regs
+	REG_L x3,  PT_GP(sp)
+	REG_L x4,  PT_TP(sp)
+	REG_L x5,  PT_T0(sp)
+	REG_L x6,  PT_T1(sp)
+	REG_L x7,  PT_T2(sp)
+	REG_L x8,  PT_S0(sp)
+	REG_L x9,  PT_S1(sp)
+	REG_L x10, PT_A0(sp)
+	REG_L x11, PT_A1(sp)
+	REG_L x12, PT_A2(sp)
+	REG_L x13, PT_A3(sp)
+	REG_L x14, PT_A4(sp)
+	REG_L x15, PT_A5(sp)
+	REG_L x16, PT_A6(sp)
+	REG_L x17, PT_A7(sp)
+	REG_L x18, PT_S2(sp)
+	REG_L x19, PT_S3(sp)
+	REG_L x20, PT_S4(sp)
+	REG_L x21, PT_S5(sp)
+	REG_L x22, PT_S6(sp)
+	REG_L x23, PT_S7(sp)
+	REG_L x24, PT_S8(sp)
+	REG_L x25, PT_S9(sp)
+	REG_L x26, PT_S10(sp)
+	REG_L x27, PT_S11(sp)
+	REG_L x28, PT_T3(sp)
+	REG_L x29, PT_T4(sp)
+	REG_L x30, PT_T5(sp)
+	REG_L x31, PT_T6(sp)
+	.endm
+
+ENTRY(kretprobe_trampoline)
+	addi sp, sp, -(PT_SIZE_ON_STACK)
+	save_all_base_regs
+
+	move a0, sp /* pt_regs */
+
+	call trampoline_probe_handler
+
+	/* use the result as the return-address */
+	move ra, a0
+
+	restore_all_base_regs
+	addi sp, sp, PT_SIZE_ON_STACK
+
+	ret
+ENDPROC(kretprobe_trampoline)
diff --git a/arch/riscv/kernel/probes/simulate-insn.c b/arch/riscv/kernel/probes/simulate-insn.c
new file mode 100644
index 000000000000..5734d9bae22f
--- /dev/null
+++ b/arch/riscv/kernel/probes/simulate-insn.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+#include <linux/bitops.h>
+#include <linux/kernel.h>
+#include <linux/kprobes.h>
+
+#include "simulate-insn.h"
+
+#define bit_at(value, bit)		((value) & (1 << (bit)))
+#define move_bit_at(value, bit, to)	((bit_at(value, bit) >> bit) << to)
+
+void __kprobes
+simulate_caddisp16(u32 opcode, long addr, struct pt_regs *regs)
+{
+	s16 imm;
+
+	/*
+	 * Immediate value layout in c.addisp16:
+	 * xxx9 xxxx x468 75xx
+	 * 1  1    8    4    0
+	 * 5  2
+	 */
+	imm = sign_extend32(
+		move_bit_at(opcode, 12, 9) |
+		move_bit_at(opcode, 6, 4) |
+		move_bit_at(opcode, 5, 6) |
+		move_bit_at(opcode, 4, 8) |
+		move_bit_at(opcode, 3, 7) |
+		move_bit_at(opcode, 2, 5),
+		9);
+
+	regs->sp += imm;
+}
diff --git a/arch/riscv/kernel/probes/simulate-insn.h b/arch/riscv/kernel/probes/simulate-insn.h
new file mode 100644
index 000000000000..dc2c06c30167
--- /dev/null
+++ b/arch/riscv/kernel/probes/simulate-insn.h
@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+
+#ifndef _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H
+#define _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H
+
+void simulate_caddisp16(u32 opcode, long addr, struct pt_regs *regs);
+
+#endif /* _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H */
diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index 24a9333dda2c..d7113178d401 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -18,6 +18,7 @@
 #include <linux/sched/signal.h>
 #include <linux/signal.h>
 #include <linux/kdebug.h>
+#include <linux/kprobes.h>
 #include <linux/uaccess.h>
 #include <linux/mm.h>
 #include <linux/module.h>
@@ -120,8 +121,14 @@ DO_ERROR_INFO(do_trap_ecall_m,
 
 asmlinkage void do_trap_break(struct pt_regs *regs)
 {
+	bool handler_found = false;
+
+#ifdef CONFIG_KPROBES
+	if (kprobe_breakpoint_handler(regs))
+		handler_found = 1;
+#endif
 #ifdef CONFIG_GENERIC_BUG
-	if (!user_mode(regs)) {
+	if (!handler_found && !user_mode(regs)) {
 		enum bug_trap_type type;
 
 		type = report_bug(regs->sepc, regs);
@@ -137,7 +144,9 @@ asmlinkage void do_trap_break(struct pt_regs *regs)
 	}
 #endif /* CONFIG_GENERIC_BUG */
 
-	force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)(regs->sepc), current);
+	if (!handler_found)
+		force_sig_fault(SIGTRAP, TRAP_BRKPT,
+			(void __user *)(regs->sepc), current);
 }
 
 #ifdef CONFIG_GENERIC_BUG
diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index 88401d5125bc..eff816e33479 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -22,6 +22,7 @@
 
 #include <linux/mm.h>
 #include <linux/kernel.h>
+#include <linux/kprobes.h>
 #include <linux/interrupt.h>
 #include <linux/perf_event.h>
 #include <linux/signal.h>
@@ -30,11 +31,33 @@
 #include <asm/pgalloc.h>
 #include <asm/ptrace.h>
 
+#ifdef CONFIG_KPROBES
+static inline int notify_page_fault(struct pt_regs *regs, unsigned int cause)
+{
+	int ret = 0;
+
+	/* kprobe_running() needs smp_processor_id() */
+	if (!user_mode(regs)) {
+		preempt_disable();
+		if (kprobe_running() && kprobe_fault_handler(regs, cause))
+			ret = 1;
+		preempt_enable();
+	}
+
+	return ret;
+}
+#else
+static inline int notify_page_fault(struct pt_regs *regs, unsigned int cause)
+{
+	return 0;
+}
+#endif
+
 /*
  * This routine handles page faults.  It determines the address and the
  * problem, and then passes it off to one of the appropriate routines.
  */
-asmlinkage void do_page_fault(struct pt_regs *regs)
+asmlinkage void __kprobes do_page_fault(struct pt_regs *regs)
 {
 	struct task_struct *tsk;
 	struct vm_area_struct *vma;
@@ -47,6 +70,9 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 	cause = regs->scause;
 	addr = regs->sbadaddr;
 
+	if (notify_page_fault(regs, cause))
+		return;
+
 	tsk = current;
 	mm = tsk->mm;
 
-- 
2.17.1


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^ permalink raw reply	[flat|nested] 18+ messages in thread

* [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support
  2018-11-13 19:58 ` [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support me
  2018-11-13 19:58   ` Patrick Stählin
@ 2018-11-14  8:37   ` mhiramat
  2018-11-14  8:37     ` Masami Hiramatsu
                       ` (2 more replies)
  1 sibling, 3 replies; 18+ messages in thread
From: mhiramat @ 2018-11-14  8:37 UTC (permalink / raw)
  To: linux-riscv

Hi Patrick,

Thank you very much for implementing kprobes on RISC-V :)

On Tue, 13 Nov 2018 20:58:04 +0100
Patrick St?hlin <me@packi.ch> wrote:

> First implementation, adapted from arm64. The C.ADDISP16 instruction
> gets simulated and the kprobes-handler called by inserting a C.EBREAK
> instruction.
> 
> C.ADDISP16 was chosen as it sets-up the stack frame for functions.
> Some work has been done to support probes on non-compressed
> instructions but there is no support yet for decoding those.

Does this only support C.ADDISP16? No other insns are supported?
Supporting 1 insn is too few I think.

Can RISC-V do single stepping? If not, we need to prepare emulator
as match as possible, or for ALU instructions, we can run it on
buffer and hook it.

> The way forward should be to uncompress the instructions for simulation
> to reduce the number of instructions used to decode  the immediate
> values on probe hit.

I have some comments on the patch, please review.

> 
> Signed-off-by: Patrick St?hlin <me@packi.ch>
> ---
>  arch/riscv/Kconfig                            |   5 +-
>  arch/riscv/include/asm/kprobes.h              |  30 ++
>  arch/riscv/include/asm/probes.h               |  26 ++
>  arch/riscv/kernel/Makefile                    |   1 +
>  arch/riscv/kernel/probes/Makefile             |   3 +
>  arch/riscv/kernel/probes/decode-insn.c        |  38 ++
>  arch/riscv/kernel/probes/decode-insn.h        |  23 +
>  arch/riscv/kernel/probes/kprobes.c            | 401 ++++++++++++++++++
>  arch/riscv/kernel/probes/kprobes_trampoline.S |  91 ++++
>  arch/riscv/kernel/probes/simulate-insn.c      |  33 ++
>  arch/riscv/kernel/probes/simulate-insn.h      |   8 +
>  arch/riscv/kernel/traps.c                     |  13 +-
>  arch/riscv/mm/fault.c                         |  28 +-
>  13 files changed, 694 insertions(+), 6 deletions(-)
>  create mode 100644 arch/riscv/include/asm/probes.h
>  create mode 100644 arch/riscv/kernel/probes/Makefile
>  create mode 100644 arch/riscv/kernel/probes/decode-insn.c
>  create mode 100644 arch/riscv/kernel/probes/decode-insn.h
>  create mode 100644 arch/riscv/kernel/probes/kprobes.c
>  create mode 100644 arch/riscv/kernel/probes/kprobes_trampoline.S
>  create mode 100644 arch/riscv/kernel/probes/simulate-insn.c
>  create mode 100644 arch/riscv/kernel/probes/simulate-insn.h
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index b157ac82d486..11ef4030e8f2 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -44,6 +44,8 @@ config RISCV
>  	select GENERIC_IRQ_MULTI_HANDLER
>  	select ARCH_HAS_PTE_SPECIAL
>  	select HAVE_REGS_AND_STACK_ACCESS_API
> +	select HAVE_KPROBES
> +	select HAVE_KRETPROBES
>  
>  config MMU
>  	def_bool y
> @@ -89,9 +91,6 @@ config PGTABLE_LEVELS
>  	default 3 if 64BIT
>  	default 2
>  
> -config HAVE_KPROBES
> -	def_bool n
> -
>  menu "Platform type"
>  
>  choice
> diff --git a/arch/riscv/include/asm/kprobes.h b/arch/riscv/include/asm/kprobes.h
> index c7eb010d1528..657adcd35a3d 100644
> --- a/arch/riscv/include/asm/kprobes.h
> +++ b/arch/riscv/include/asm/kprobes.h
> @@ -19,4 +19,34 @@
>  
>  #include <asm-generic/kprobes.h>
>  
> +#ifdef CONFIG_KPROBES
> +#include <linux/types.h>
> +#include <linux/ptrace.h>
> +#include <linux/percpu.h>
> +
> +#define flush_insn_slot(p)		do { } while (0)
> +#define kretprobe_blacklist_size	0
> +
> +#include <asm/probes.h>
> +
> +struct prev_kprobe {
> +	struct kprobe *kp;
> +	unsigned int status;
> +};
> +
> +/* per-cpu kprobe control block */
> +struct kprobe_ctlblk {
> +	unsigned int kprobe_status;
> +	struct prev_kprobe prev_kprobe;
> +};
> +
> +void arch_remove_kprobe(struct kprobe *p);
> +int kprobe_fault_handler(struct pt_regs *regs, unsigned int cause);
> +int kprobe_exceptions_notify(struct notifier_block *self,
> +			     unsigned long val, void *data);
> +int kprobe_breakpoint_handler(struct pt_regs *regs);
> +void kretprobe_trampoline(void);
> +void __kprobes *trampoline_probe_handler(struct pt_regs *regs);
> +
> +#endif /* CONFIG_KPROBES */
>  #endif /* _RISCV_KPROBES_H */
> diff --git a/arch/riscv/include/asm/probes.h b/arch/riscv/include/asm/probes.h
> new file mode 100644
> index 000000000000..64cf12567539
> --- /dev/null
> +++ b/arch/riscv/include/asm/probes.h
> @@ -0,0 +1,26 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Based on arch/arm64/include/asm/probes.h
> + *
> + * Copyright (C) 2013 Linaro Limited
> + */
> +#ifndef _RISCV_PROBES_H
> +#define _RISCV_PROBES_H
> +
> +typedef u32 probe_opcode_t;
> +typedef void (probes_handler_t) (u32 opcode, long addr, struct pt_regs *);
> +
> +/* architecture specific copy of original instruction */
> +struct arch_probe_insn {
> +	probes_handler_t *handler;
> +	/* restore address after simulation */
> +	unsigned long restore;
> +};
> +#ifdef CONFIG_KPROBES
> +typedef u32 kprobe_opcode_t;
> +struct arch_specific_insn {
> +	struct arch_probe_insn api;
> +};
> +#endif

Are there any reason of putting this kprobes dedicated data structure here?

> +
> +#endif /* _RISCV_PROBES_H */
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index f13f7f276639..5360a445b9d3 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -28,6 +28,7 @@ obj-y	+= stacktrace.o
>  obj-y	+= vdso.o
>  obj-y	+= cacheinfo.o
>  obj-y	+= vdso/
> +obj-y	+= probes/
>  
>  CFLAGS_setup.o := -mcmodel=medany
>  
> diff --git a/arch/riscv/kernel/probes/Makefile b/arch/riscv/kernel/probes/Makefile
> new file mode 100644
> index 000000000000..144d1c1743fb
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/Makefile
> @@ -0,0 +1,3 @@
> +# SPDX-License-Identifier: GPL-2.0
> +obj-$(CONFIG_KPROBES)		+= kprobes.o kprobes_trampoline.o \
> +				   decode-insn.o simulate-insn.o
> diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c
> new file mode 100644
> index 000000000000..2d8f46f4c2e7
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/decode-insn.c
> @@ -0,0 +1,38 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +#include <linux/kernel.h>
> +#include <linux/kprobes.h>
> +#include <linux/module.h>
> +#include <linux/kallsyms.h>
> +#include <asm/sections.h>
> +
> +#include "decode-insn.h"
> +#include "simulate-insn.h"
> +
> +#define C_ADDISP16_MASK 0x6F83
> +#define C_ADDISP16_VAL  0x6101
> +
> +/* Return:
> + *   INSN_REJECTED     If instruction is one not allowed to kprobe,
> + *   INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot.
> + */
> +enum probe_insn __kprobes
> +riscv_probe_decode_insn(kprobe_opcode_t *addr, struct arch_probe_insn *api)

Please don't use __kprobes anymore. That is old stlye, instead, please
use NOKPROBE_SYMBOL() or nokprobe_inline for static-inline function.
(NOKPROBE_SYMBOL() will make the symbol non-inline always)

> +{
> +	probe_opcode_t insn = le32_to_cpu(*addr);
> +
> +	if (!is_compressed_insn(insn)) {
> +		pr_warn("Can't handle non-compressed instruction %x\n", insn);
> +		return INSN_REJECTED;
> +	}
> +
> +	/* c.addisp16 imm */
> +	if ((insn & C_ADDISP16_MASK) == C_ADDISP16_VAL) {
> +		api->handler = simulate_caddisp16;
> +	} else {
> +		pr_warn("Rejected unknown instruction %x\n", insn);
> +		return INSN_REJECTED;
> +	}
> +
> +	return INSN_GOOD_NO_SLOT;
> +}
> diff --git a/arch/riscv/kernel/probes/decode-insn.h b/arch/riscv/kernel/probes/decode-insn.h
> new file mode 100644
> index 000000000000..0053ed6a308a
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/decode-insn.h
> @@ -0,0 +1,23 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +#ifndef _RISCV_KERNEL_KPROBES_DECODE_INSN_H
> +#define _RISCV_KERNEL_KPROBES_DECODE_INSN_H
> +
> +#include <asm/sections.h>
> +#include <asm/kprobes.h>
> +
> +enum probe_insn {
> +	INSN_REJECTED,
> +	INSN_GOOD_NO_SLOT,
> +};
> +
> +/*
> + * Compressed instruction format:
> + * xxxxxxxxxxxxxxaa where aa != 11
> + */
> +#define is_compressed_insn(insn) ((insn & 0x3) != 0x3)
> +
> +#ifdef CONFIG_KPROBES
> +enum probe_insn __kprobes
> +riscv_probe_decode_insn(kprobe_opcode_t *addr, struct arch_probe_insn *asi);
> +#endif
> +#endif /* _RISCV_KERNEL_KPROBES_DECODE_INSN_H */
> diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
> new file mode 100644
> index 000000000000..3c7b5cf72ee1
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/kprobes.c
> @@ -0,0 +1,401 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +/*
> + * Kprobes support for RISC-V
> + *
> + * Author: Patrick St?hlin <me@packi.ch>
> + */
> +#include <linux/kprobes.h>
> +#include <linux/extable.h>
> +#include <linux/slab.h>
> +#include <asm/ptrace.h>
> +#include <linux/uaccess.h>
> +#include <asm/sections.h>
> +
> +#include "decode-insn.h"
> +
> +DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
> +DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
> +
> +static void __kprobes
> +post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
> +
> +static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
> +{
> +	if (is_compressed_insn(opcode))
> +		*(u16 *)addr = cpu_to_le16(opcode);
> +	else
> +		*addr = cpu_to_le32(opcode);
> +
> +	return 0;
> +}
> +
> +static void __kprobes arch_prepare_simulate(struct kprobe *p)
> +{
> +	unsigned long offset = is_compressed_insn(p->opcode) ? 2 : 4;
> +
> +	p->ainsn.api.restore = (unsigned long)p->addr + offset;
> +}
> +
> +static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
> +{
> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +
> +	if (p->ainsn.api.handler)
> +		p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);

it seems api.handler must be here, 

> +
> +	/* single instruction simulated, now go for post processing */
> +	post_kprobe_handler(kcb, regs);
> +}
> +
> +int __kprobes arch_prepare_kprobe(struct kprobe *p)
> +{
> +	unsigned long probe_addr = (unsigned long)p->addr;
> +	extern char __start_rodata[];
> +	extern char __end_rodata[];
> +
> +	if (probe_addr & 0x1) {
> +		pr_warn("Address not aligned.\n");
> +		return -EINVAL;
> +	}
> +
> +	/* copy instruction */
> +	p->opcode = le32_to_cpu(*p->addr);
> +
> +	if (probe_addr >= (unsigned long) __start_rodata &&
> +	    probe_addr <= (unsigned long) __end_rodata) {
> +		return -EINVAL;
> +	}
> +
> +	/* decode instruction */
> +	switch (riscv_probe_decode_insn(p->addr, &p->ainsn.api)) {
> +	case INSN_REJECTED:	/* insn not supported */
> +		return -EINVAL;
> +
> +	case INSN_GOOD_NO_SLOT:	/* insn needs simulation */
> +		break;
> +	}
> +
> +	arch_prepare_simulate(p);
> +
> +	return 0;
> +}
> +
> +#define C_EBREAK_OPCODE 0x9002
> +
> +/* arm kprobe: install breakpoint in text */
> +void __kprobes arch_arm_kprobe(struct kprobe *p)
> +{
> +	patch_text(p->addr, C_EBREAK_OPCODE);
> +}
> +
> +/* disarm kprobe: remove breakpoint from text */
> +void __kprobes arch_disarm_kprobe(struct kprobe *p)
> +{
> +	patch_text(p->addr, p->opcode);
> +}
> +
> +void __kprobes arch_remove_kprobe(struct kprobe *p)
> +{
> +}
> +
> +static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
> +{
> +	kcb->prev_kprobe.kp = kprobe_running();
> +	kcb->prev_kprobe.status = kcb->kprobe_status;
> +}
> +
> +static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
> +{
> +	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
> +	kcb->kprobe_status = kcb->prev_kprobe.status;
> +}
> +
> +static void __kprobes set_current_kprobe(struct kprobe *p)
> +{
> +	__this_cpu_write(current_kprobe, p);
> +}
> +
> +static void __kprobes simulate(struct kprobe *p,
> +			       struct pt_regs *regs,
> +			       struct kprobe_ctlblk *kcb, int reenter)
> +{
> +	if (reenter) {
> +		save_previous_kprobe(kcb);
> +		set_current_kprobe(p);
> +		kcb->kprobe_status = KPROBE_REENTER;
> +	} else {
> +		kcb->kprobe_status = KPROBE_HIT_SS;
> +	}
> +
> +	arch_simulate_insn(p, regs);
> +}
> +
> +static int __kprobes reenter_kprobe(struct kprobe *p,
> +				    struct pt_regs *regs,
> +				    struct kprobe_ctlblk *kcb)
> +{
> +	switch (kcb->kprobe_status) {
> +	case KPROBE_HIT_SSDONE:
> +	case KPROBE_HIT_ACTIVE:
> +		kprobes_inc_nmissed_count(p);
> +		simulate(p, regs, kcb, 1);
> +		break;
> +	case KPROBE_HIT_SS:
> +	case KPROBE_REENTER:
> +		pr_warn("Unrecoverable kprobe detected.\n");
> +		dump_kprobe(p);
> +		BUG();
> +		break;
> +	default:
> +		WARN_ON(1);
> +		return 0;
> +	}
> +
> +	return 1;

If this always return 1, we can make it void return.

> +}
> +
> +static void __kprobes
> +post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
> +{
> +	struct kprobe *cur = kprobe_running();
> +
> +	if (!cur)
> +		return;
> +
> +	/* return addr restore if non-branching insn */
> +	if (cur->ainsn.api.restore != 0)
> +		instruction_pointer_set(regs, cur->ainsn.api.restore);
> +
> +	/* restore back original saved kprobe variables and continue */
> +	if (kcb->kprobe_status == KPROBE_REENTER) {
> +		restore_previous_kprobe(kcb);
> +		return;
> +	}
> +	/* call post handler */
> +	kcb->kprobe_status = KPROBE_HIT_SSDONE;
> +	if (cur->post_handler)	{
> +		/* post_handler can hit breakpoint and single step
> +		 * again, so we enable D-flag for recursive exception.
> +		 */
> +		cur->post_handler(cur, regs, 0);
> +	}
> +
> +	reset_current_kprobe();
> +}
> +
> +int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int cause)
> +{
> +	struct kprobe *cur = kprobe_running();
> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +
> +	switch (kcb->kprobe_status) {
> +	case KPROBE_HIT_SS:
> +	case KPROBE_REENTER:
> +		/*
> +		 * We are here because the instruction being single
> +		 * stepped caused a page fault. We reset the current
> +		 * kprobe and the ip points back to the probe address
> +		 * and allow the page fault handler to continue as a
> +		 * normal page fault.
> +		 */
> +		instruction_pointer_set(regs, (unsigned long) cur->addr);
> +		if (!instruction_pointer(regs))
> +			BUG();

Use BUG_ON().

> +
> +		if (kcb->kprobe_status == KPROBE_REENTER)
> +			restore_previous_kprobe(kcb);
> +		else
> +			reset_current_kprobe();
> +
> +		break;
> +	case KPROBE_HIT_ACTIVE:
> +	case KPROBE_HIT_SSDONE:
> +		/*
> +		 * We increment the nmissed count for accounting,
> +		 * we can also use npre/npostfault count for accounting
> +		 * these specific fault cases.
> +		 */
> +		kprobes_inc_nmissed_count(cur);
> +
> +		/*
> +		 * We come here because instructions in the pre/post
> +		 * handler caused the page_fault, this could happen
> +		 * if handler tries to access user space by
> +		 * copy_from_user(), get_user() etc. Let the
> +		 * user-specified handler try to fix it first.
> +		 */
> +		if (cur->fault_handler && cur->fault_handler(cur, regs, cause))
> +			return 1;
> +
> +		/*
> +		 * In case the user-specified fault handler returned
> +		 * zero, try to fix up.
> +		 */
> +		if (fixup_exception(regs))
> +			return 1;
> +	}
> +	return 0;
> +}
> +
> +static void __kprobes kprobe_handler(struct pt_regs *regs)
> +{

Does this handler run under local IRQ disabled? (for making sure)

> +	struct kprobe *p, *cur_kprobe;
> +	struct kprobe_ctlblk *kcb;
> +	unsigned long addr = instruction_pointer(regs);
> +
> +	kcb = get_kprobe_ctlblk();
> +	cur_kprobe = kprobe_running();
> +
> +	p = get_kprobe((kprobe_opcode_t *) addr);
> +
> +	if (p) {
> +		if (cur_kprobe) {
> +			if (reenter_kprobe(p, regs, kcb))
> +				return;
> +		} else {
> +			/* Probe hit */
> +			set_current_kprobe(p);
> +			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> +
> +			/*
> +			 * If we have no pre-handler or it returned 0, we
> +			 * continue with normal processing.  If we have a
> +			 * pre-handler and it returned non-zero, it will
> +			 * modify the execution path and no need to single
> +			 * stepping. Let's just reset current kprobe and exit.
> +			 *
> +			 * pre_handler can hit a breakpoint and can step thru
> +			 * before return, keep PSTATE D-flag enabled until
> +			 * pre_handler return back.

Is this true on RISC-V too?

> +			 */
> +			if (!p->pre_handler || !p->pre_handler(p, regs))
> +				simulate(p, regs, kcb, 0);
> +			else
> +				reset_current_kprobe();
> +		}
> +	}
> +	/*
> +	 * The breakpoint instruction was removed right
> +	 * after we hit it.  Another cpu has removed
> +	 * either a probepoint or a debugger breakpoint
> +	 * at this address.  In either case, no further
> +	 * handling of this interrupt is appropriate.
> +	 * Return back to original instruction, and continue.
> +	 */

This should return 0 if it doesn't handle anything, but if it handles c.break
should return 1.

> +}
> +
> +int __kprobes
> +kprobe_breakpoint_handler(struct pt_regs *regs)
> +{
> +	kprobe_handler(regs);
> +	return 1;

Why don't you call kprobe_handler directly?

> +}
> +
> +bool arch_within_kprobe_blacklist(unsigned long addr)
> +{
> +	if ((addr >= (unsigned long)__kprobes_text_start &&
> +	    addr < (unsigned long)__kprobes_text_end) ||
> +	    (addr >= (unsigned long)__entry_text_start &&
> +	    addr < (unsigned long)__entry_text_end) ||
> +	    !!search_exception_tables(addr))
> +		return true;
> +
> +	return false;
> +}
> +
> +void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
> +{
> +	struct kretprobe_instance *ri = NULL;
> +	struct hlist_head *head, empty_rp;
> +	struct hlist_node *tmp;
> +	unsigned long flags, orig_ret_address = 0;
> +	unsigned long trampoline_address =
> +		(unsigned long)&kretprobe_trampoline;
> +	kprobe_opcode_t *correct_ret_addr = NULL;
> +

	It seems you don't setup instruction_pointer.

> +	INIT_HLIST_HEAD(&empty_rp);
> +	kretprobe_hash_lock(current, &head, &flags);
> +
> +	/*
> +	 * It is possible to have multiple instances associated with a given
> +	 * task either because multiple functions in the call path have
> +	 * return probes installed on them, and/or more than one
> +	 * return probe was registered for a target function.
> +	 *
> +	 * We can handle this because:
> +	 *     - instances are always pushed into the head of the list
> +	 *     - when multiple return probes are registered for the same
> +	 *	 function, the (chronologically) first instance's ret_addr
> +	 *	 will be the real return address, and all the rest will
> +	 *	 point to kretprobe_trampoline.
> +	 */
> +	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
> +		if (ri->task != current)
> +			/* another task is sharing our hash bucket */
> +			continue;
> +
> +		orig_ret_address = (unsigned long)ri->ret_addr;
> +
> +		if (orig_ret_address != trampoline_address)
> +			/*
> +			 * This is the real return address. Any other
> +			 * instances associated with this task are for
> +			 * other calls deeper on the call stack
> +			 */
> +			break;
> +	}
> +
> +	kretprobe_assert(ri, orig_ret_address, trampoline_address);
> +
> +	correct_ret_addr = ri->ret_addr;
> +	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
> +		if (ri->task != current)
> +			/* another task is sharing our hash bucket */
> +			continue;
> +
> +		orig_ret_address = (unsigned long)ri->ret_addr;
> +		if (ri->rp && ri->rp->handler) {
> +			__this_cpu_write(current_kprobe, &ri->rp->kp);
> +			get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
> +			ri->ret_addr = correct_ret_addr;
> +			ri->rp->handler(ri, regs);
> +			__this_cpu_write(current_kprobe, NULL);
> +		}
> +
> +		recycle_rp_inst(ri, &empty_rp);
> +
> +		if (orig_ret_address != trampoline_address)
> +			/*
> +			 * This is the real return address. Any other
> +			 * instances associated with this task are for
> +			 * other calls deeper on the call stack
> +			 */
> +			break;
> +	}
> +
> +	kretprobe_hash_unlock(current, &flags);
> +
> +	hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
> +		hlist_del(&ri->hlist);
> +		kfree(ri);
> +	}
> +	return (void *)orig_ret_address;
> +}
> +
> +void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
> +				      struct pt_regs *regs)
> +{
> +	ri->ret_addr = (kprobe_opcode_t *)regs->ra;
> +	regs->ra = (long)&kretprobe_trampoline;
> +}
> +
> +int __kprobes arch_trampoline_kprobe(struct kprobe *p)
> +{
> +	return 0;
> +}
> +
> +int __init arch_init_kprobes(void)
> +{
> +	return 0;
> +}
> diff --git a/arch/riscv/kernel/probes/kprobes_trampoline.S b/arch/riscv/kernel/probes/kprobes_trampoline.S
> new file mode 100644
> index 000000000000..c7ceda9556a3
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/kprobes_trampoline.S
> @@ -0,0 +1,91 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +
> +#include <linux/linkage.h>
> +
> +#include <asm/asm.h>
> +#include <asm/asm-offsets.h>
> +
> +	.text
> +	.altmacro
> +
> +	.macro save_all_base_regs
> +	REG_S x1,  PT_RA(sp)
> +	REG_S x3,  PT_GP(sp)
> +	REG_S x4,  PT_TP(sp)
> +	REG_S x5,  PT_T0(sp)
> +	REG_S x6,  PT_T1(sp)
> +	REG_S x7,  PT_T2(sp)
> +	REG_S x8,  PT_S0(sp)
> +	REG_S x9,  PT_S1(sp)
> +	REG_S x10, PT_A0(sp)
> +	REG_S x11, PT_A1(sp)
> +	REG_S x12, PT_A2(sp)
> +	REG_S x13, PT_A3(sp)
> +	REG_S x14, PT_A4(sp)
> +	REG_S x15, PT_A5(sp)
> +	REG_S x16, PT_A6(sp)
> +	REG_S x17, PT_A7(sp)
> +	REG_S x18, PT_S2(sp)
> +	REG_S x19, PT_S3(sp)
> +	REG_S x20, PT_S4(sp)
> +	REG_S x21, PT_S5(sp)
> +	REG_S x22, PT_S6(sp)
> +	REG_S x23, PT_S7(sp)
> +	REG_S x24, PT_S8(sp)
> +	REG_S x25, PT_S9(sp)
> +	REG_S x26, PT_S10(sp)
> +	REG_S x27, PT_S11(sp)
> +	REG_S x28, PT_T3(sp)
> +	REG_S x29, PT_T4(sp)
> +	REG_S x30, PT_T5(sp)
> +	REG_S x31, PT_T6(sp)
> +	.endm
> +
> +	.macro restore_all_base_regs
> +	REG_L x3,  PT_GP(sp)
> +	REG_L x4,  PT_TP(sp)
> +	REG_L x5,  PT_T0(sp)
> +	REG_L x6,  PT_T1(sp)
> +	REG_L x7,  PT_T2(sp)
> +	REG_L x8,  PT_S0(sp)
> +	REG_L x9,  PT_S1(sp)
> +	REG_L x10, PT_A0(sp)
> +	REG_L x11, PT_A1(sp)
> +	REG_L x12, PT_A2(sp)
> +	REG_L x13, PT_A3(sp)
> +	REG_L x14, PT_A4(sp)
> +	REG_L x15, PT_A5(sp)
> +	REG_L x16, PT_A6(sp)
> +	REG_L x17, PT_A7(sp)
> +	REG_L x18, PT_S2(sp)
> +	REG_L x19, PT_S3(sp)
> +	REG_L x20, PT_S4(sp)
> +	REG_L x21, PT_S5(sp)
> +	REG_L x22, PT_S6(sp)
> +	REG_L x23, PT_S7(sp)
> +	REG_L x24, PT_S8(sp)
> +	REG_L x25, PT_S9(sp)
> +	REG_L x26, PT_S10(sp)
> +	REG_L x27, PT_S11(sp)
> +	REG_L x28, PT_T3(sp)
> +	REG_L x29, PT_T4(sp)
> +	REG_L x30, PT_T5(sp)
> +	REG_L x31, PT_T6(sp)
> +	.endm
> +
> +ENTRY(kretprobe_trampoline)
> +	addi sp, sp, -(PT_SIZE_ON_STACK)
> +	save_all_base_regs
> +
> +	move a0, sp /* pt_regs */
> +
> +	call trampoline_probe_handler
> +
> +	/* use the result as the return-address */
> +	move ra, a0
> +
> +	restore_all_base_regs
> +	addi sp, sp, PT_SIZE_ON_STACK
> +
> +	ret
> +ENDPROC(kretprobe_trampoline)
> diff --git a/arch/riscv/kernel/probes/simulate-insn.c b/arch/riscv/kernel/probes/simulate-insn.c
> new file mode 100644
> index 000000000000..5734d9bae22f
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/simulate-insn.c
> @@ -0,0 +1,33 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +#include <linux/bitops.h>
> +#include <linux/kernel.h>
> +#include <linux/kprobes.h>
> +
> +#include "simulate-insn.h"
> +
> +#define bit_at(value, bit)		((value) & (1 << (bit)))
> +#define move_bit_at(value, bit, to)	((bit_at(value, bit) >> bit) << to)
> +
> +void __kprobes
> +simulate_caddisp16(u32 opcode, long addr, struct pt_regs *regs)
> +{
> +	s16 imm;
> +
> +	/*
> +	 * Immediate value layout in c.addisp16:
> +	 * xxx9 xxxx x468 75xx
> +	 * 1  1    8    4    0
> +	 * 5  2
> +	 */
> +	imm = sign_extend32(
> +		move_bit_at(opcode, 12, 9) |
> +		move_bit_at(opcode, 6, 4) |
> +		move_bit_at(opcode, 5, 6) |
> +		move_bit_at(opcode, 4, 8) |
> +		move_bit_at(opcode, 3, 7) |
> +		move_bit_at(opcode, 2, 5),
> +		9);
> +
> +	regs->sp += imm;

What about updating regs->sepc?

> +}
> diff --git a/arch/riscv/kernel/probes/simulate-insn.h b/arch/riscv/kernel/probes/simulate-insn.h
> new file mode 100644
> index 000000000000..dc2c06c30167
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/simulate-insn.h
> @@ -0,0 +1,8 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +
> +#ifndef _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H
> +#define _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H
> +
> +void simulate_caddisp16(u32 opcode, long addr, struct pt_regs *regs);
> +
> +#endif /* _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H */
> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> index 24a9333dda2c..d7113178d401 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -18,6 +18,7 @@
>  #include <linux/sched/signal.h>
>  #include <linux/signal.h>
>  #include <linux/kdebug.h>
> +#include <linux/kprobes.h>
>  #include <linux/uaccess.h>
>  #include <linux/mm.h>
>  #include <linux/module.h>
> @@ -120,8 +121,14 @@ DO_ERROR_INFO(do_trap_ecall_m,
>  
>  asmlinkage void do_trap_break(struct pt_regs *regs)
>  {
> +	bool handler_found = false;
> +
> +#ifdef CONFIG_KPROBES
> +	if (kprobe_breakpoint_handler(regs))
> +		handler_found = 1;

Why don't you just return from here?

> +#endif
>  #ifdef CONFIG_GENERIC_BUG
> -	if (!user_mode(regs)) {
> +	if (!handler_found && !user_mode(regs)) {
>  		enum bug_trap_type type;
>  
>  		type = report_bug(regs->sepc, regs);
> @@ -137,7 +144,9 @@ asmlinkage void do_trap_break(struct pt_regs *regs)
>  	}
>  #endif /* CONFIG_GENERIC_BUG */
>  
> -	force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)(regs->sepc), current);
> +	if (!handler_found)
> +		force_sig_fault(SIGTRAP, TRAP_BRKPT,
> +			(void __user *)(regs->sepc), current);
>  }
>  
>  #ifdef CONFIG_GENERIC_BUG
> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
> index 88401d5125bc..eff816e33479 100644
> --- a/arch/riscv/mm/fault.c
> +++ b/arch/riscv/mm/fault.c
> @@ -22,6 +22,7 @@
>  
>  #include <linux/mm.h>
>  #include <linux/kernel.h>
> +#include <linux/kprobes.h>
>  #include <linux/interrupt.h>
>  #include <linux/perf_event.h>
>  #include <linux/signal.h>
> @@ -30,11 +31,33 @@
>  #include <asm/pgalloc.h>
>  #include <asm/ptrace.h>
>  
> +#ifdef CONFIG_KPROBES
> +static inline int notify_page_fault(struct pt_regs *regs, unsigned int cause)

please use nokprobe_inline.

> +{
> +	int ret = 0;
> +
> +	/* kprobe_running() needs smp_processor_id() */
> +	if (!user_mode(regs)) {
> +		preempt_disable();
> +		if (kprobe_running() && kprobe_fault_handler(regs, cause))
> +			ret = 1;
> +		preempt_enable();
> +	}
> +
> +	return ret;
> +}
> +#else
> +static inline int notify_page_fault(struct pt_regs *regs, unsigned int cause)
> +{
> +	return 0;
> +}
> +#endif
> +
>  /*
>   * This routine handles page faults.  It determines the address and the
>   * problem, and then passes it off to one of the appropriate routines.
>   */
> -asmlinkage void do_page_fault(struct pt_regs *regs)
> +asmlinkage void __kprobes do_page_fault(struct pt_regs *regs)
>  {
>  	struct task_struct *tsk;
>  	struct vm_area_struct *vma;
> @@ -47,6 +70,9 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
>  	cause = regs->scause;
>  	addr = regs->sbadaddr;
>  
> +	if (notify_page_fault(regs, cause))
> +		return;
> +
>  	tsk = current;
>  	mm = tsk->mm;
>  
> -- 
> 2.17.1
> 

Thank you,

-- 
Masami Hiramatsu <mhiramat@kernel.org>

^ permalink raw reply	[flat|nested] 18+ messages in thread

* Re: [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support
  2018-11-14  8:37   ` mhiramat
@ 2018-11-14  8:37     ` Masami Hiramatsu
  2018-11-14 15:49     ` mhiramat
  2018-11-14 20:52     ` me
  2 siblings, 0 replies; 18+ messages in thread
From: Masami Hiramatsu @ 2018-11-14  8:37 UTC (permalink / raw)
  To: Patrick Stählin
  Cc: Albert Ou, Anders Roxell, Andrew Morton, Alan Kao,
	Catalin Marinas, Palmer Dabbelt, Will Deacon, linux-kernel,
	Al Viro, Souptick Joarder, Zong Li, Thomas Gleixner,
	Masami Hiramatsu, linux-riscv, Jim Wilson, zhong jiang,
	Ingo Molnar, Luc Van Oostenryck, Eric W. Biederman

Hi Patrick,

Thank you very much for implementing kprobes on RISC-V :)

On Tue, 13 Nov 2018 20:58:04 +0100
Patrick Stählin <me@packi.ch> wrote:

> First implementation, adapted from arm64. The C.ADDISP16 instruction
> gets simulated and the kprobes-handler called by inserting a C.EBREAK
> instruction.
> 
> C.ADDISP16 was chosen as it sets-up the stack frame for functions.
> Some work has been done to support probes on non-compressed
> instructions but there is no support yet for decoding those.

Does this only support C.ADDISP16? No other insns are supported?
Supporting 1 insn is too few I think.

Can RISC-V do single stepping? If not, we need to prepare emulator
as match as possible, or for ALU instructions, we can run it on
buffer and hook it.

> The way forward should be to uncompress the instructions for simulation
> to reduce the number of instructions used to decode  the immediate
> values on probe hit.

I have some comments on the patch, please review.

> 
> Signed-off-by: Patrick Stählin <me@packi.ch>
> ---
>  arch/riscv/Kconfig                            |   5 +-
>  arch/riscv/include/asm/kprobes.h              |  30 ++
>  arch/riscv/include/asm/probes.h               |  26 ++
>  arch/riscv/kernel/Makefile                    |   1 +
>  arch/riscv/kernel/probes/Makefile             |   3 +
>  arch/riscv/kernel/probes/decode-insn.c        |  38 ++
>  arch/riscv/kernel/probes/decode-insn.h        |  23 +
>  arch/riscv/kernel/probes/kprobes.c            | 401 ++++++++++++++++++
>  arch/riscv/kernel/probes/kprobes_trampoline.S |  91 ++++
>  arch/riscv/kernel/probes/simulate-insn.c      |  33 ++
>  arch/riscv/kernel/probes/simulate-insn.h      |   8 +
>  arch/riscv/kernel/traps.c                     |  13 +-
>  arch/riscv/mm/fault.c                         |  28 +-
>  13 files changed, 694 insertions(+), 6 deletions(-)
>  create mode 100644 arch/riscv/include/asm/probes.h
>  create mode 100644 arch/riscv/kernel/probes/Makefile
>  create mode 100644 arch/riscv/kernel/probes/decode-insn.c
>  create mode 100644 arch/riscv/kernel/probes/decode-insn.h
>  create mode 100644 arch/riscv/kernel/probes/kprobes.c
>  create mode 100644 arch/riscv/kernel/probes/kprobes_trampoline.S
>  create mode 100644 arch/riscv/kernel/probes/simulate-insn.c
>  create mode 100644 arch/riscv/kernel/probes/simulate-insn.h
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index b157ac82d486..11ef4030e8f2 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -44,6 +44,8 @@ config RISCV
>  	select GENERIC_IRQ_MULTI_HANDLER
>  	select ARCH_HAS_PTE_SPECIAL
>  	select HAVE_REGS_AND_STACK_ACCESS_API
> +	select HAVE_KPROBES
> +	select HAVE_KRETPROBES
>  
>  config MMU
>  	def_bool y
> @@ -89,9 +91,6 @@ config PGTABLE_LEVELS
>  	default 3 if 64BIT
>  	default 2
>  
> -config HAVE_KPROBES
> -	def_bool n
> -
>  menu "Platform type"
>  
>  choice
> diff --git a/arch/riscv/include/asm/kprobes.h b/arch/riscv/include/asm/kprobes.h
> index c7eb010d1528..657adcd35a3d 100644
> --- a/arch/riscv/include/asm/kprobes.h
> +++ b/arch/riscv/include/asm/kprobes.h
> @@ -19,4 +19,34 @@
>  
>  #include <asm-generic/kprobes.h>
>  
> +#ifdef CONFIG_KPROBES
> +#include <linux/types.h>
> +#include <linux/ptrace.h>
> +#include <linux/percpu.h>
> +
> +#define flush_insn_slot(p)		do { } while (0)
> +#define kretprobe_blacklist_size	0
> +
> +#include <asm/probes.h>
> +
> +struct prev_kprobe {
> +	struct kprobe *kp;
> +	unsigned int status;
> +};
> +
> +/* per-cpu kprobe control block */
> +struct kprobe_ctlblk {
> +	unsigned int kprobe_status;
> +	struct prev_kprobe prev_kprobe;
> +};
> +
> +void arch_remove_kprobe(struct kprobe *p);
> +int kprobe_fault_handler(struct pt_regs *regs, unsigned int cause);
> +int kprobe_exceptions_notify(struct notifier_block *self,
> +			     unsigned long val, void *data);
> +int kprobe_breakpoint_handler(struct pt_regs *regs);
> +void kretprobe_trampoline(void);
> +void __kprobes *trampoline_probe_handler(struct pt_regs *regs);
> +
> +#endif /* CONFIG_KPROBES */
>  #endif /* _RISCV_KPROBES_H */
> diff --git a/arch/riscv/include/asm/probes.h b/arch/riscv/include/asm/probes.h
> new file mode 100644
> index 000000000000..64cf12567539
> --- /dev/null
> +++ b/arch/riscv/include/asm/probes.h
> @@ -0,0 +1,26 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Based on arch/arm64/include/asm/probes.h
> + *
> + * Copyright (C) 2013 Linaro Limited
> + */
> +#ifndef _RISCV_PROBES_H
> +#define _RISCV_PROBES_H
> +
> +typedef u32 probe_opcode_t;
> +typedef void (probes_handler_t) (u32 opcode, long addr, struct pt_regs *);
> +
> +/* architecture specific copy of original instruction */
> +struct arch_probe_insn {
> +	probes_handler_t *handler;
> +	/* restore address after simulation */
> +	unsigned long restore;
> +};
> +#ifdef CONFIG_KPROBES
> +typedef u32 kprobe_opcode_t;
> +struct arch_specific_insn {
> +	struct arch_probe_insn api;
> +};
> +#endif

Are there any reason of putting this kprobes dedicated data structure here?

> +
> +#endif /* _RISCV_PROBES_H */
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index f13f7f276639..5360a445b9d3 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -28,6 +28,7 @@ obj-y	+= stacktrace.o
>  obj-y	+= vdso.o
>  obj-y	+= cacheinfo.o
>  obj-y	+= vdso/
> +obj-y	+= probes/
>  
>  CFLAGS_setup.o := -mcmodel=medany
>  
> diff --git a/arch/riscv/kernel/probes/Makefile b/arch/riscv/kernel/probes/Makefile
> new file mode 100644
> index 000000000000..144d1c1743fb
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/Makefile
> @@ -0,0 +1,3 @@
> +# SPDX-License-Identifier: GPL-2.0
> +obj-$(CONFIG_KPROBES)		+= kprobes.o kprobes_trampoline.o \
> +				   decode-insn.o simulate-insn.o
> diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c
> new file mode 100644
> index 000000000000..2d8f46f4c2e7
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/decode-insn.c
> @@ -0,0 +1,38 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +#include <linux/kernel.h>
> +#include <linux/kprobes.h>
> +#include <linux/module.h>
> +#include <linux/kallsyms.h>
> +#include <asm/sections.h>
> +
> +#include "decode-insn.h"
> +#include "simulate-insn.h"
> +
> +#define C_ADDISP16_MASK 0x6F83
> +#define C_ADDISP16_VAL  0x6101
> +
> +/* Return:
> + *   INSN_REJECTED     If instruction is one not allowed to kprobe,
> + *   INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot.
> + */
> +enum probe_insn __kprobes
> +riscv_probe_decode_insn(kprobe_opcode_t *addr, struct arch_probe_insn *api)

Please don't use __kprobes anymore. That is old stlye, instead, please
use NOKPROBE_SYMBOL() or nokprobe_inline for static-inline function.
(NOKPROBE_SYMBOL() will make the symbol non-inline always)

> +{
> +	probe_opcode_t insn = le32_to_cpu(*addr);
> +
> +	if (!is_compressed_insn(insn)) {
> +		pr_warn("Can't handle non-compressed instruction %x\n", insn);
> +		return INSN_REJECTED;
> +	}
> +
> +	/* c.addisp16 imm */
> +	if ((insn & C_ADDISP16_MASK) == C_ADDISP16_VAL) {
> +		api->handler = simulate_caddisp16;
> +	} else {
> +		pr_warn("Rejected unknown instruction %x\n", insn);
> +		return INSN_REJECTED;
> +	}
> +
> +	return INSN_GOOD_NO_SLOT;
> +}
> diff --git a/arch/riscv/kernel/probes/decode-insn.h b/arch/riscv/kernel/probes/decode-insn.h
> new file mode 100644
> index 000000000000..0053ed6a308a
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/decode-insn.h
> @@ -0,0 +1,23 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +#ifndef _RISCV_KERNEL_KPROBES_DECODE_INSN_H
> +#define _RISCV_KERNEL_KPROBES_DECODE_INSN_H
> +
> +#include <asm/sections.h>
> +#include <asm/kprobes.h>
> +
> +enum probe_insn {
> +	INSN_REJECTED,
> +	INSN_GOOD_NO_SLOT,
> +};
> +
> +/*
> + * Compressed instruction format:
> + * xxxxxxxxxxxxxxaa where aa != 11
> + */
> +#define is_compressed_insn(insn) ((insn & 0x3) != 0x3)
> +
> +#ifdef CONFIG_KPROBES
> +enum probe_insn __kprobes
> +riscv_probe_decode_insn(kprobe_opcode_t *addr, struct arch_probe_insn *asi);
> +#endif
> +#endif /* _RISCV_KERNEL_KPROBES_DECODE_INSN_H */
> diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
> new file mode 100644
> index 000000000000..3c7b5cf72ee1
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/kprobes.c
> @@ -0,0 +1,401 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +/*
> + * Kprobes support for RISC-V
> + *
> + * Author: Patrick Stählin <me@packi.ch>
> + */
> +#include <linux/kprobes.h>
> +#include <linux/extable.h>
> +#include <linux/slab.h>
> +#include <asm/ptrace.h>
> +#include <linux/uaccess.h>
> +#include <asm/sections.h>
> +
> +#include "decode-insn.h"
> +
> +DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
> +DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
> +
> +static void __kprobes
> +post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
> +
> +static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
> +{
> +	if (is_compressed_insn(opcode))
> +		*(u16 *)addr = cpu_to_le16(opcode);
> +	else
> +		*addr = cpu_to_le32(opcode);
> +
> +	return 0;
> +}
> +
> +static void __kprobes arch_prepare_simulate(struct kprobe *p)
> +{
> +	unsigned long offset = is_compressed_insn(p->opcode) ? 2 : 4;
> +
> +	p->ainsn.api.restore = (unsigned long)p->addr + offset;
> +}
> +
> +static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
> +{
> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +
> +	if (p->ainsn.api.handler)
> +		p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);

it seems api.handler must be here, 

> +
> +	/* single instruction simulated, now go for post processing */
> +	post_kprobe_handler(kcb, regs);
> +}
> +
> +int __kprobes arch_prepare_kprobe(struct kprobe *p)
> +{
> +	unsigned long probe_addr = (unsigned long)p->addr;
> +	extern char __start_rodata[];
> +	extern char __end_rodata[];
> +
> +	if (probe_addr & 0x1) {
> +		pr_warn("Address not aligned.\n");
> +		return -EINVAL;
> +	}
> +
> +	/* copy instruction */
> +	p->opcode = le32_to_cpu(*p->addr);
> +
> +	if (probe_addr >= (unsigned long) __start_rodata &&
> +	    probe_addr <= (unsigned long) __end_rodata) {
> +		return -EINVAL;
> +	}
> +
> +	/* decode instruction */
> +	switch (riscv_probe_decode_insn(p->addr, &p->ainsn.api)) {
> +	case INSN_REJECTED:	/* insn not supported */
> +		return -EINVAL;
> +
> +	case INSN_GOOD_NO_SLOT:	/* insn needs simulation */
> +		break;
> +	}
> +
> +	arch_prepare_simulate(p);
> +
> +	return 0;
> +}
> +
> +#define C_EBREAK_OPCODE 0x9002
> +
> +/* arm kprobe: install breakpoint in text */
> +void __kprobes arch_arm_kprobe(struct kprobe *p)
> +{
> +	patch_text(p->addr, C_EBREAK_OPCODE);
> +}
> +
> +/* disarm kprobe: remove breakpoint from text */
> +void __kprobes arch_disarm_kprobe(struct kprobe *p)
> +{
> +	patch_text(p->addr, p->opcode);
> +}
> +
> +void __kprobes arch_remove_kprobe(struct kprobe *p)
> +{
> +}
> +
> +static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
> +{
> +	kcb->prev_kprobe.kp = kprobe_running();
> +	kcb->prev_kprobe.status = kcb->kprobe_status;
> +}
> +
> +static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
> +{
> +	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
> +	kcb->kprobe_status = kcb->prev_kprobe.status;
> +}
> +
> +static void __kprobes set_current_kprobe(struct kprobe *p)
> +{
> +	__this_cpu_write(current_kprobe, p);
> +}
> +
> +static void __kprobes simulate(struct kprobe *p,
> +			       struct pt_regs *regs,
> +			       struct kprobe_ctlblk *kcb, int reenter)
> +{
> +	if (reenter) {
> +		save_previous_kprobe(kcb);
> +		set_current_kprobe(p);
> +		kcb->kprobe_status = KPROBE_REENTER;
> +	} else {
> +		kcb->kprobe_status = KPROBE_HIT_SS;
> +	}
> +
> +	arch_simulate_insn(p, regs);
> +}
> +
> +static int __kprobes reenter_kprobe(struct kprobe *p,
> +				    struct pt_regs *regs,
> +				    struct kprobe_ctlblk *kcb)
> +{
> +	switch (kcb->kprobe_status) {
> +	case KPROBE_HIT_SSDONE:
> +	case KPROBE_HIT_ACTIVE:
> +		kprobes_inc_nmissed_count(p);
> +		simulate(p, regs, kcb, 1);
> +		break;
> +	case KPROBE_HIT_SS:
> +	case KPROBE_REENTER:
> +		pr_warn("Unrecoverable kprobe detected.\n");
> +		dump_kprobe(p);
> +		BUG();
> +		break;
> +	default:
> +		WARN_ON(1);
> +		return 0;
> +	}
> +
> +	return 1;

If this always return 1, we can make it void return.

> +}
> +
> +static void __kprobes
> +post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
> +{
> +	struct kprobe *cur = kprobe_running();
> +
> +	if (!cur)
> +		return;
> +
> +	/* return addr restore if non-branching insn */
> +	if (cur->ainsn.api.restore != 0)
> +		instruction_pointer_set(regs, cur->ainsn.api.restore);
> +
> +	/* restore back original saved kprobe variables and continue */
> +	if (kcb->kprobe_status == KPROBE_REENTER) {
> +		restore_previous_kprobe(kcb);
> +		return;
> +	}
> +	/* call post handler */
> +	kcb->kprobe_status = KPROBE_HIT_SSDONE;
> +	if (cur->post_handler)	{
> +		/* post_handler can hit breakpoint and single step
> +		 * again, so we enable D-flag for recursive exception.
> +		 */
> +		cur->post_handler(cur, regs, 0);
> +	}
> +
> +	reset_current_kprobe();
> +}
> +
> +int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int cause)
> +{
> +	struct kprobe *cur = kprobe_running();
> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +
> +	switch (kcb->kprobe_status) {
> +	case KPROBE_HIT_SS:
> +	case KPROBE_REENTER:
> +		/*
> +		 * We are here because the instruction being single
> +		 * stepped caused a page fault. We reset the current
> +		 * kprobe and the ip points back to the probe address
> +		 * and allow the page fault handler to continue as a
> +		 * normal page fault.
> +		 */
> +		instruction_pointer_set(regs, (unsigned long) cur->addr);
> +		if (!instruction_pointer(regs))
> +			BUG();

Use BUG_ON().

> +
> +		if (kcb->kprobe_status == KPROBE_REENTER)
> +			restore_previous_kprobe(kcb);
> +		else
> +			reset_current_kprobe();
> +
> +		break;
> +	case KPROBE_HIT_ACTIVE:
> +	case KPROBE_HIT_SSDONE:
> +		/*
> +		 * We increment the nmissed count for accounting,
> +		 * we can also use npre/npostfault count for accounting
> +		 * these specific fault cases.
> +		 */
> +		kprobes_inc_nmissed_count(cur);
> +
> +		/*
> +		 * We come here because instructions in the pre/post
> +		 * handler caused the page_fault, this could happen
> +		 * if handler tries to access user space by
> +		 * copy_from_user(), get_user() etc. Let the
> +		 * user-specified handler try to fix it first.
> +		 */
> +		if (cur->fault_handler && cur->fault_handler(cur, regs, cause))
> +			return 1;
> +
> +		/*
> +		 * In case the user-specified fault handler returned
> +		 * zero, try to fix up.
> +		 */
> +		if (fixup_exception(regs))
> +			return 1;
> +	}
> +	return 0;
> +}
> +
> +static void __kprobes kprobe_handler(struct pt_regs *regs)
> +{

Does this handler run under local IRQ disabled? (for making sure)

> +	struct kprobe *p, *cur_kprobe;
> +	struct kprobe_ctlblk *kcb;
> +	unsigned long addr = instruction_pointer(regs);
> +
> +	kcb = get_kprobe_ctlblk();
> +	cur_kprobe = kprobe_running();
> +
> +	p = get_kprobe((kprobe_opcode_t *) addr);
> +
> +	if (p) {
> +		if (cur_kprobe) {
> +			if (reenter_kprobe(p, regs, kcb))
> +				return;
> +		} else {
> +			/* Probe hit */
> +			set_current_kprobe(p);
> +			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> +
> +			/*
> +			 * If we have no pre-handler or it returned 0, we
> +			 * continue with normal processing.  If we have a
> +			 * pre-handler and it returned non-zero, it will
> +			 * modify the execution path and no need to single
> +			 * stepping. Let's just reset current kprobe and exit.
> +			 *
> +			 * pre_handler can hit a breakpoint and can step thru
> +			 * before return, keep PSTATE D-flag enabled until
> +			 * pre_handler return back.

Is this true on RISC-V too?

> +			 */
> +			if (!p->pre_handler || !p->pre_handler(p, regs))
> +				simulate(p, regs, kcb, 0);
> +			else
> +				reset_current_kprobe();
> +		}
> +	}
> +	/*
> +	 * The breakpoint instruction was removed right
> +	 * after we hit it.  Another cpu has removed
> +	 * either a probepoint or a debugger breakpoint
> +	 * at this address.  In either case, no further
> +	 * handling of this interrupt is appropriate.
> +	 * Return back to original instruction, and continue.
> +	 */

This should return 0 if it doesn't handle anything, but if it handles c.break
should return 1.

> +}
> +
> +int __kprobes
> +kprobe_breakpoint_handler(struct pt_regs *regs)
> +{
> +	kprobe_handler(regs);
> +	return 1;

Why don't you call kprobe_handler directly?

> +}
> +
> +bool arch_within_kprobe_blacklist(unsigned long addr)
> +{
> +	if ((addr >= (unsigned long)__kprobes_text_start &&
> +	    addr < (unsigned long)__kprobes_text_end) ||
> +	    (addr >= (unsigned long)__entry_text_start &&
> +	    addr < (unsigned long)__entry_text_end) ||
> +	    !!search_exception_tables(addr))
> +		return true;
> +
> +	return false;
> +}
> +
> +void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
> +{
> +	struct kretprobe_instance *ri = NULL;
> +	struct hlist_head *head, empty_rp;
> +	struct hlist_node *tmp;
> +	unsigned long flags, orig_ret_address = 0;
> +	unsigned long trampoline_address =
> +		(unsigned long)&kretprobe_trampoline;
> +	kprobe_opcode_t *correct_ret_addr = NULL;
> +

	It seems you don't setup instruction_pointer.

> +	INIT_HLIST_HEAD(&empty_rp);
> +	kretprobe_hash_lock(current, &head, &flags);
> +
> +	/*
> +	 * It is possible to have multiple instances associated with a given
> +	 * task either because multiple functions in the call path have
> +	 * return probes installed on them, and/or more than one
> +	 * return probe was registered for a target function.
> +	 *
> +	 * We can handle this because:
> +	 *     - instances are always pushed into the head of the list
> +	 *     - when multiple return probes are registered for the same
> +	 *	 function, the (chronologically) first instance's ret_addr
> +	 *	 will be the real return address, and all the rest will
> +	 *	 point to kretprobe_trampoline.
> +	 */
> +	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
> +		if (ri->task != current)
> +			/* another task is sharing our hash bucket */
> +			continue;
> +
> +		orig_ret_address = (unsigned long)ri->ret_addr;
> +
> +		if (orig_ret_address != trampoline_address)
> +			/*
> +			 * This is the real return address. Any other
> +			 * instances associated with this task are for
> +			 * other calls deeper on the call stack
> +			 */
> +			break;
> +	}
> +
> +	kretprobe_assert(ri, orig_ret_address, trampoline_address);
> +
> +	correct_ret_addr = ri->ret_addr;
> +	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
> +		if (ri->task != current)
> +			/* another task is sharing our hash bucket */
> +			continue;
> +
> +		orig_ret_address = (unsigned long)ri->ret_addr;
> +		if (ri->rp && ri->rp->handler) {
> +			__this_cpu_write(current_kprobe, &ri->rp->kp);
> +			get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
> +			ri->ret_addr = correct_ret_addr;
> +			ri->rp->handler(ri, regs);
> +			__this_cpu_write(current_kprobe, NULL);
> +		}
> +
> +		recycle_rp_inst(ri, &empty_rp);
> +
> +		if (orig_ret_address != trampoline_address)
> +			/*
> +			 * This is the real return address. Any other
> +			 * instances associated with this task are for
> +			 * other calls deeper on the call stack
> +			 */
> +			break;
> +	}
> +
> +	kretprobe_hash_unlock(current, &flags);
> +
> +	hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
> +		hlist_del(&ri->hlist);
> +		kfree(ri);
> +	}
> +	return (void *)orig_ret_address;
> +}
> +
> +void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
> +				      struct pt_regs *regs)
> +{
> +	ri->ret_addr = (kprobe_opcode_t *)regs->ra;
> +	regs->ra = (long)&kretprobe_trampoline;
> +}
> +
> +int __kprobes arch_trampoline_kprobe(struct kprobe *p)
> +{
> +	return 0;
> +}
> +
> +int __init arch_init_kprobes(void)
> +{
> +	return 0;
> +}
> diff --git a/arch/riscv/kernel/probes/kprobes_trampoline.S b/arch/riscv/kernel/probes/kprobes_trampoline.S
> new file mode 100644
> index 000000000000..c7ceda9556a3
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/kprobes_trampoline.S
> @@ -0,0 +1,91 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +
> +#include <linux/linkage.h>
> +
> +#include <asm/asm.h>
> +#include <asm/asm-offsets.h>
> +
> +	.text
> +	.altmacro
> +
> +	.macro save_all_base_regs
> +	REG_S x1,  PT_RA(sp)
> +	REG_S x3,  PT_GP(sp)
> +	REG_S x4,  PT_TP(sp)
> +	REG_S x5,  PT_T0(sp)
> +	REG_S x6,  PT_T1(sp)
> +	REG_S x7,  PT_T2(sp)
> +	REG_S x8,  PT_S0(sp)
> +	REG_S x9,  PT_S1(sp)
> +	REG_S x10, PT_A0(sp)
> +	REG_S x11, PT_A1(sp)
> +	REG_S x12, PT_A2(sp)
> +	REG_S x13, PT_A3(sp)
> +	REG_S x14, PT_A4(sp)
> +	REG_S x15, PT_A5(sp)
> +	REG_S x16, PT_A6(sp)
> +	REG_S x17, PT_A7(sp)
> +	REG_S x18, PT_S2(sp)
> +	REG_S x19, PT_S3(sp)
> +	REG_S x20, PT_S4(sp)
> +	REG_S x21, PT_S5(sp)
> +	REG_S x22, PT_S6(sp)
> +	REG_S x23, PT_S7(sp)
> +	REG_S x24, PT_S8(sp)
> +	REG_S x25, PT_S9(sp)
> +	REG_S x26, PT_S10(sp)
> +	REG_S x27, PT_S11(sp)
> +	REG_S x28, PT_T3(sp)
> +	REG_S x29, PT_T4(sp)
> +	REG_S x30, PT_T5(sp)
> +	REG_S x31, PT_T6(sp)
> +	.endm
> +
> +	.macro restore_all_base_regs
> +	REG_L x3,  PT_GP(sp)
> +	REG_L x4,  PT_TP(sp)
> +	REG_L x5,  PT_T0(sp)
> +	REG_L x6,  PT_T1(sp)
> +	REG_L x7,  PT_T2(sp)
> +	REG_L x8,  PT_S0(sp)
> +	REG_L x9,  PT_S1(sp)
> +	REG_L x10, PT_A0(sp)
> +	REG_L x11, PT_A1(sp)
> +	REG_L x12, PT_A2(sp)
> +	REG_L x13, PT_A3(sp)
> +	REG_L x14, PT_A4(sp)
> +	REG_L x15, PT_A5(sp)
> +	REG_L x16, PT_A6(sp)
> +	REG_L x17, PT_A7(sp)
> +	REG_L x18, PT_S2(sp)
> +	REG_L x19, PT_S3(sp)
> +	REG_L x20, PT_S4(sp)
> +	REG_L x21, PT_S5(sp)
> +	REG_L x22, PT_S6(sp)
> +	REG_L x23, PT_S7(sp)
> +	REG_L x24, PT_S8(sp)
> +	REG_L x25, PT_S9(sp)
> +	REG_L x26, PT_S10(sp)
> +	REG_L x27, PT_S11(sp)
> +	REG_L x28, PT_T3(sp)
> +	REG_L x29, PT_T4(sp)
> +	REG_L x30, PT_T5(sp)
> +	REG_L x31, PT_T6(sp)
> +	.endm
> +
> +ENTRY(kretprobe_trampoline)
> +	addi sp, sp, -(PT_SIZE_ON_STACK)
> +	save_all_base_regs
> +
> +	move a0, sp /* pt_regs */
> +
> +	call trampoline_probe_handler
> +
> +	/* use the result as the return-address */
> +	move ra, a0
> +
> +	restore_all_base_regs
> +	addi sp, sp, PT_SIZE_ON_STACK
> +
> +	ret
> +ENDPROC(kretprobe_trampoline)
> diff --git a/arch/riscv/kernel/probes/simulate-insn.c b/arch/riscv/kernel/probes/simulate-insn.c
> new file mode 100644
> index 000000000000..5734d9bae22f
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/simulate-insn.c
> @@ -0,0 +1,33 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +#include <linux/bitops.h>
> +#include <linux/kernel.h>
> +#include <linux/kprobes.h>
> +
> +#include "simulate-insn.h"
> +
> +#define bit_at(value, bit)		((value) & (1 << (bit)))
> +#define move_bit_at(value, bit, to)	((bit_at(value, bit) >> bit) << to)
> +
> +void __kprobes
> +simulate_caddisp16(u32 opcode, long addr, struct pt_regs *regs)
> +{
> +	s16 imm;
> +
> +	/*
> +	 * Immediate value layout in c.addisp16:
> +	 * xxx9 xxxx x468 75xx
> +	 * 1  1    8    4    0
> +	 * 5  2
> +	 */
> +	imm = sign_extend32(
> +		move_bit_at(opcode, 12, 9) |
> +		move_bit_at(opcode, 6, 4) |
> +		move_bit_at(opcode, 5, 6) |
> +		move_bit_at(opcode, 4, 8) |
> +		move_bit_at(opcode, 3, 7) |
> +		move_bit_at(opcode, 2, 5),
> +		9);
> +
> +	regs->sp += imm;

What about updating regs->sepc?

> +}
> diff --git a/arch/riscv/kernel/probes/simulate-insn.h b/arch/riscv/kernel/probes/simulate-insn.h
> new file mode 100644
> index 000000000000..dc2c06c30167
> --- /dev/null
> +++ b/arch/riscv/kernel/probes/simulate-insn.h
> @@ -0,0 +1,8 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +
> +#ifndef _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H
> +#define _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H
> +
> +void simulate_caddisp16(u32 opcode, long addr, struct pt_regs *regs);
> +
> +#endif /* _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H */
> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> index 24a9333dda2c..d7113178d401 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -18,6 +18,7 @@
>  #include <linux/sched/signal.h>
>  #include <linux/signal.h>
>  #include <linux/kdebug.h>
> +#include <linux/kprobes.h>
>  #include <linux/uaccess.h>
>  #include <linux/mm.h>
>  #include <linux/module.h>
> @@ -120,8 +121,14 @@ DO_ERROR_INFO(do_trap_ecall_m,
>  
>  asmlinkage void do_trap_break(struct pt_regs *regs)
>  {
> +	bool handler_found = false;
> +
> +#ifdef CONFIG_KPROBES
> +	if (kprobe_breakpoint_handler(regs))
> +		handler_found = 1;

Why don't you just return from here?

> +#endif
>  #ifdef CONFIG_GENERIC_BUG
> -	if (!user_mode(regs)) {
> +	if (!handler_found && !user_mode(regs)) {
>  		enum bug_trap_type type;
>  
>  		type = report_bug(regs->sepc, regs);
> @@ -137,7 +144,9 @@ asmlinkage void do_trap_break(struct pt_regs *regs)
>  	}
>  #endif /* CONFIG_GENERIC_BUG */
>  
> -	force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)(regs->sepc), current);
> +	if (!handler_found)
> +		force_sig_fault(SIGTRAP, TRAP_BRKPT,
> +			(void __user *)(regs->sepc), current);
>  }
>  
>  #ifdef CONFIG_GENERIC_BUG
> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
> index 88401d5125bc..eff816e33479 100644
> --- a/arch/riscv/mm/fault.c
> +++ b/arch/riscv/mm/fault.c
> @@ -22,6 +22,7 @@
>  
>  #include <linux/mm.h>
>  #include <linux/kernel.h>
> +#include <linux/kprobes.h>
>  #include <linux/interrupt.h>
>  #include <linux/perf_event.h>
>  #include <linux/signal.h>
> @@ -30,11 +31,33 @@
>  #include <asm/pgalloc.h>
>  #include <asm/ptrace.h>
>  
> +#ifdef CONFIG_KPROBES
> +static inline int notify_page_fault(struct pt_regs *regs, unsigned int cause)

please use nokprobe_inline.

> +{
> +	int ret = 0;
> +
> +	/* kprobe_running() needs smp_processor_id() */
> +	if (!user_mode(regs)) {
> +		preempt_disable();
> +		if (kprobe_running() && kprobe_fault_handler(regs, cause))
> +			ret = 1;
> +		preempt_enable();
> +	}
> +
> +	return ret;
> +}
> +#else
> +static inline int notify_page_fault(struct pt_regs *regs, unsigned int cause)
> +{
> +	return 0;
> +}
> +#endif
> +
>  /*
>   * This routine handles page faults.  It determines the address and the
>   * problem, and then passes it off to one of the appropriate routines.
>   */
> -asmlinkage void do_page_fault(struct pt_regs *regs)
> +asmlinkage void __kprobes do_page_fault(struct pt_regs *regs)
>  {
>  	struct task_struct *tsk;
>  	struct vm_area_struct *vma;
> @@ -47,6 +70,9 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
>  	cause = regs->scause;
>  	addr = regs->sbadaddr;
>  
> +	if (notify_page_fault(regs, cause))
> +		return;
> +
>  	tsk = current;
>  	mm = tsk->mm;
>  
> -- 
> 2.17.1
> 

Thank you,

-- 
Masami Hiramatsu <mhiramat@kernel.org>

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^ permalink raw reply	[flat|nested] 18+ messages in thread

* [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support
  2018-11-14  8:37   ` mhiramat
  2018-11-14  8:37     ` Masami Hiramatsu
@ 2018-11-14 15:49     ` mhiramat
  2018-11-14 15:49       ` Masami Hiramatsu
  2018-11-14 21:10       ` me
  2018-11-14 20:52     ` me
  2 siblings, 2 replies; 18+ messages in thread
From: mhiramat @ 2018-11-14 15:49 UTC (permalink / raw)
  To: linux-riscv

On Wed, 14 Nov 2018 00:37:30 -0800
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> > +
> > +static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
> > +{
> > +	if (is_compressed_insn(opcode))
> > +		*(u16 *)addr = cpu_to_le16(opcode);
> > +	else
> > +		*addr = cpu_to_le32(opcode);
> > +

BTW, don't RISC-V need any i-cache flush and per-core serialization
for patching the text area? (and no text_mutex protection?)

> > diff --git a/arch/riscv/kernel/probes/kprobes_trampoline.S b/arch/riscv/kernel/probes/kprobes_trampoline.S
> > new file mode 100644
> > index 000000000000..c7ceda9556a3
> > --- /dev/null
> > +++ b/arch/riscv/kernel/probes/kprobes_trampoline.S
> > @@ -0,0 +1,91 @@
> > +/* SPDX-License-Identifier: GPL-2.0+ */
> > +
> > +#include <linux/linkage.h>
> > +
> > +#include <asm/asm.h>
> > +#include <asm/asm-offsets.h>
> > +
> > +	.text
> > +	.altmacro
> > +
> > +	.macro save_all_base_regs
> > +	REG_S x1,  PT_RA(sp)
> > +	REG_S x3,  PT_GP(sp)
> > +	REG_S x4,  PT_TP(sp)
> > +	REG_S x5,  PT_T0(sp)
> > +	REG_S x6,  PT_T1(sp)
> > +	REG_S x7,  PT_T2(sp)
> > +	REG_S x8,  PT_S0(sp)
> > +	REG_S x9,  PT_S1(sp)
> > +	REG_S x10, PT_A0(sp)
> > +	REG_S x11, PT_A1(sp)
> > +	REG_S x12, PT_A2(sp)
> > +	REG_S x13, PT_A3(sp)
> > +	REG_S x14, PT_A4(sp)
> > +	REG_S x15, PT_A5(sp)
> > +	REG_S x16, PT_A6(sp)
> > +	REG_S x17, PT_A7(sp)
> > +	REG_S x18, PT_S2(sp)
> > +	REG_S x19, PT_S3(sp)
> > +	REG_S x20, PT_S4(sp)
> > +	REG_S x21, PT_S5(sp)
> > +	REG_S x22, PT_S6(sp)
> > +	REG_S x23, PT_S7(sp)
> > +	REG_S x24, PT_S8(sp)
> > +	REG_S x25, PT_S9(sp)
> > +	REG_S x26, PT_S10(sp)
> > +	REG_S x27, PT_S11(sp)
> > +	REG_S x28, PT_T3(sp)
> > +	REG_S x29, PT_T4(sp)
> > +	REG_S x30, PT_T5(sp)
> > +	REG_S x31, PT_T6(sp)
> > +	.endm
> > +
> > +	.macro restore_all_base_regs
> > +	REG_L x3,  PT_GP(sp)
> > +	REG_L x4,  PT_TP(sp)
> > +	REG_L x5,  PT_T0(sp)
> > +	REG_L x6,  PT_T1(sp)
> > +	REG_L x7,  PT_T2(sp)
> > +	REG_L x8,  PT_S0(sp)
> > +	REG_L x9,  PT_S1(sp)
> > +	REG_L x10, PT_A0(sp)
> > +	REG_L x11, PT_A1(sp)
> > +	REG_L x12, PT_A2(sp)
> > +	REG_L x13, PT_A3(sp)
> > +	REG_L x14, PT_A4(sp)
> > +	REG_L x15, PT_A5(sp)
> > +	REG_L x16, PT_A6(sp)
> > +	REG_L x17, PT_A7(sp)
> > +	REG_L x18, PT_S2(sp)
> > +	REG_L x19, PT_S3(sp)
> > +	REG_L x20, PT_S4(sp)
> > +	REG_L x21, PT_S5(sp)
> > +	REG_L x22, PT_S6(sp)
> > +	REG_L x23, PT_S7(sp)
> > +	REG_L x24, PT_S8(sp)
> > +	REG_L x25, PT_S9(sp)
> > +	REG_L x26, PT_S10(sp)
> > +	REG_L x27, PT_S11(sp)
> > +	REG_L x28, PT_T3(sp)
> > +	REG_L x29, PT_T4(sp)
> > +	REG_L x30, PT_T5(sp)
> > +	REG_L x31, PT_T6(sp)
> > +	.endm


It seems thses macros can be (partially?) shared with entry.S

Thank you,

-- 
Masami Hiramatsu <mhiramat@kernel.org>

^ permalink raw reply	[flat|nested] 18+ messages in thread

* Re: [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support
  2018-11-14 15:49     ` mhiramat
@ 2018-11-14 15:49       ` Masami Hiramatsu
  2018-11-14 21:10       ` me
  1 sibling, 0 replies; 18+ messages in thread
From: Masami Hiramatsu @ 2018-11-14 15:49 UTC (permalink / raw)
  To: Masami Hiramatsu
  Cc: Patrick Stählin, Albert Ou, Anders Roxell, Andrew Morton,
	Alan Kao, Catalin Marinas, Palmer Dabbelt, Will Deacon,
	linux-kernel, Al Viro, Souptick Joarder, Zong Li,
	Thomas Gleixner, Eric W. Biederman, linux-riscv, zhong jiang,
	Ingo Molnar, Luc Van Oostenryck, Jim Wilson

On Wed, 14 Nov 2018 00:37:30 -0800
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> > +
> > +static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
> > +{
> > +	if (is_compressed_insn(opcode))
> > +		*(u16 *)addr = cpu_to_le16(opcode);
> > +	else
> > +		*addr = cpu_to_le32(opcode);
> > +

BTW, don't RISC-V need any i-cache flush and per-core serialization
for patching the text area? (and no text_mutex protection?)

> > diff --git a/arch/riscv/kernel/probes/kprobes_trampoline.S b/arch/riscv/kernel/probes/kprobes_trampoline.S
> > new file mode 100644
> > index 000000000000..c7ceda9556a3
> > --- /dev/null
> > +++ b/arch/riscv/kernel/probes/kprobes_trampoline.S
> > @@ -0,0 +1,91 @@
> > +/* SPDX-License-Identifier: GPL-2.0+ */
> > +
> > +#include <linux/linkage.h>
> > +
> > +#include <asm/asm.h>
> > +#include <asm/asm-offsets.h>
> > +
> > +	.text
> > +	.altmacro
> > +
> > +	.macro save_all_base_regs
> > +	REG_S x1,  PT_RA(sp)
> > +	REG_S x3,  PT_GP(sp)
> > +	REG_S x4,  PT_TP(sp)
> > +	REG_S x5,  PT_T0(sp)
> > +	REG_S x6,  PT_T1(sp)
> > +	REG_S x7,  PT_T2(sp)
> > +	REG_S x8,  PT_S0(sp)
> > +	REG_S x9,  PT_S1(sp)
> > +	REG_S x10, PT_A0(sp)
> > +	REG_S x11, PT_A1(sp)
> > +	REG_S x12, PT_A2(sp)
> > +	REG_S x13, PT_A3(sp)
> > +	REG_S x14, PT_A4(sp)
> > +	REG_S x15, PT_A5(sp)
> > +	REG_S x16, PT_A6(sp)
> > +	REG_S x17, PT_A7(sp)
> > +	REG_S x18, PT_S2(sp)
> > +	REG_S x19, PT_S3(sp)
> > +	REG_S x20, PT_S4(sp)
> > +	REG_S x21, PT_S5(sp)
> > +	REG_S x22, PT_S6(sp)
> > +	REG_S x23, PT_S7(sp)
> > +	REG_S x24, PT_S8(sp)
> > +	REG_S x25, PT_S9(sp)
> > +	REG_S x26, PT_S10(sp)
> > +	REG_S x27, PT_S11(sp)
> > +	REG_S x28, PT_T3(sp)
> > +	REG_S x29, PT_T4(sp)
> > +	REG_S x30, PT_T5(sp)
> > +	REG_S x31, PT_T6(sp)
> > +	.endm
> > +
> > +	.macro restore_all_base_regs
> > +	REG_L x3,  PT_GP(sp)
> > +	REG_L x4,  PT_TP(sp)
> > +	REG_L x5,  PT_T0(sp)
> > +	REG_L x6,  PT_T1(sp)
> > +	REG_L x7,  PT_T2(sp)
> > +	REG_L x8,  PT_S0(sp)
> > +	REG_L x9,  PT_S1(sp)
> > +	REG_L x10, PT_A0(sp)
> > +	REG_L x11, PT_A1(sp)
> > +	REG_L x12, PT_A2(sp)
> > +	REG_L x13, PT_A3(sp)
> > +	REG_L x14, PT_A4(sp)
> > +	REG_L x15, PT_A5(sp)
> > +	REG_L x16, PT_A6(sp)
> > +	REG_L x17, PT_A7(sp)
> > +	REG_L x18, PT_S2(sp)
> > +	REG_L x19, PT_S3(sp)
> > +	REG_L x20, PT_S4(sp)
> > +	REG_L x21, PT_S5(sp)
> > +	REG_L x22, PT_S6(sp)
> > +	REG_L x23, PT_S7(sp)
> > +	REG_L x24, PT_S8(sp)
> > +	REG_L x25, PT_S9(sp)
> > +	REG_L x26, PT_S10(sp)
> > +	REG_L x27, PT_S11(sp)
> > +	REG_L x28, PT_T3(sp)
> > +	REG_L x29, PT_T4(sp)
> > +	REG_L x30, PT_T5(sp)
> > +	REG_L x31, PT_T6(sp)
> > +	.endm


It seems thses macros can be (partially?) shared with entry.S

Thank you,

-- 
Masami Hiramatsu <mhiramat@kernel.org>

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

^ permalink raw reply	[flat|nested] 18+ messages in thread

* [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support
  2018-11-14  8:37   ` mhiramat
  2018-11-14  8:37     ` Masami Hiramatsu
  2018-11-14 15:49     ` mhiramat
@ 2018-11-14 20:52     ` me
  2018-11-14 20:52       ` Patrick Staehlin
  2018-11-15  8:41       ` mhiramat
  2 siblings, 2 replies; 18+ messages in thread
From: me @ 2018-11-14 20:52 UTC (permalink / raw)
  To: linux-riscv

Hi Masami,

thank you for your remarks.

On 14.11.18 09:37, Masami Hiramatsu wrote>
> Thank you very much for implementing kprobes on RISC-V :)
> 
> On Tue, 13 Nov 2018 20:58:04 +0100
> Patrick St?hlin <me@packi.ch> wrote:
> 
>> First implementation, adapted from arm64. The C.ADDISP16 instruction
>> gets simulated and the kprobes-handler called by inserting a C.EBREAK
>> instruction.
>>
>> C.ADDISP16 was chosen as it sets-up the stack frame for functions.
>> Some work has been done to support probes on non-compressed
>> instructions but there is no support yet for decoding those.
> 
> Does this only support C.ADDISP16? No other insns are supported?
> Supporting 1 insn is too few I think.

At the moment, yes. I'm waiting for some input from somebody with deeper
insights into the RISC-V architecture than me before implementing more
instructions, should solution I've chosen be woefully inadequate.

> Can RISC-V do single stepping? If not, we need to prepare emulator
> as match as possible, or for ALU instructions, we can run it on
> buffer and hook it.

The debug-specification is still a draft but there are some softcores
that implement it. But even if it was finalized I don't think this will
be made a mandatory extension so we need to simulate/emulate a good part
of the instruction set anyway.

>> The way forward should be to uncompress the instructions for simulation
>> to reduce the number of instructions used to decode  the immediate
>> values on probe hit.
> 
> I have some comments on the patch, please review.
> 
>>
>> Signed-off-by: Patrick St?hlin <me@packi.ch>
>> ---
>>  arch/riscv/Kconfig                            |   5 +-
>>  arch/riscv/include/asm/kprobes.h              |  30 ++
>>  arch/riscv/include/asm/probes.h               |  26 ++
>>  arch/riscv/kernel/Makefile                    |   1 +
>>  arch/riscv/kernel/probes/Makefile             |   3 +
>>  arch/riscv/kernel/probes/decode-insn.c        |  38 ++
>>  arch/riscv/kernel/probes/decode-insn.h        |  23 +
>>  arch/riscv/kernel/probes/kprobes.c            | 401 ++++++++++++++++++
>>  arch/riscv/kernel/probes/kprobes_trampoline.S |  91 ++++
>>  arch/riscv/kernel/probes/simulate-insn.c      |  33 ++
>>  arch/riscv/kernel/probes/simulate-insn.h      |   8 +
>>  arch/riscv/kernel/traps.c                     |  13 +-
>>  arch/riscv/mm/fault.c                         |  28 +-
>>  13 files changed, 694 insertions(+), 6 deletions(-)
>>  create mode 100644 arch/riscv/include/asm/probes.h
>>  create mode 100644 arch/riscv/kernel/probes/Makefile
>>  create mode 100644 arch/riscv/kernel/probes/decode-insn.c
>>  create mode 100644 arch/riscv/kernel/probes/decode-insn.h
>>  create mode 100644 arch/riscv/kernel/probes/kprobes.c
>>  create mode 100644 arch/riscv/kernel/probes/kprobes_trampoline.S
>>  create mode 100644 arch/riscv/kernel/probes/simulate-insn.c
>>  create mode 100644 arch/riscv/kernel/probes/simulate-insn.h
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index b157ac82d486..11ef4030e8f2 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -44,6 +44,8 @@ config RISCV
>>  	select GENERIC_IRQ_MULTI_HANDLER
>>  	select ARCH_HAS_PTE_SPECIAL
>>  	select HAVE_REGS_AND_STACK_ACCESS_API
>> +	select HAVE_KPROBES
>> +	select HAVE_KRETPROBES
>>  
>>  config MMU
>>  	def_bool y
>> @@ -89,9 +91,6 @@ config PGTABLE_LEVELS
>>  	default 3 if 64BIT
>>  	default 2
>>  
>> -config HAVE_KPROBES
>> -	def_bool n
>> -
>>  menu "Platform type"
>>  
>>  choice
>> diff --git a/arch/riscv/include/asm/kprobes.h b/arch/riscv/include/asm/kprobes.h
>> index c7eb010d1528..657adcd35a3d 100644
>> --- a/arch/riscv/include/asm/kprobes.h
>> +++ b/arch/riscv/include/asm/kprobes.h
>> @@ -19,4 +19,34 @@
>>  
>>  #include <asm-generic/kprobes.h>
>>  
>> +#ifdef CONFIG_KPROBES
>> +#include <linux/types.h>
>> +#include <linux/ptrace.h>
>> +#include <linux/percpu.h>
>> +
>> +#define flush_insn_slot(p)		do { } while (0)
>> +#define kretprobe_blacklist_size	0
>> +
>> +#include <asm/probes.h>
>> +
>> +struct prev_kprobe {
>> +	struct kprobe *kp;
>> +	unsigned int status;
>> +};
>> +
>> +/* per-cpu kprobe control block */
>> +struct kprobe_ctlblk {
>> +	unsigned int kprobe_status;
>> +	struct prev_kprobe prev_kprobe;
>> +};
>> +
>> +void arch_remove_kprobe(struct kprobe *p);
>> +int kprobe_fault_handler(struct pt_regs *regs, unsigned int cause);
>> +int kprobe_exceptions_notify(struct notifier_block *self,
>> +			     unsigned long val, void *data);
>> +int kprobe_breakpoint_handler(struct pt_regs *regs);
>> +void kretprobe_trampoline(void);
>> +void __kprobes *trampoline_probe_handler(struct pt_regs *regs);
>> +
>> +#endif /* CONFIG_KPROBES */
>>  #endif /* _RISCV_KPROBES_H */
>> diff --git a/arch/riscv/include/asm/probes.h b/arch/riscv/include/asm/probes.h
>> new file mode 100644
>> index 000000000000..64cf12567539
>> --- /dev/null
>> +++ b/arch/riscv/include/asm/probes.h
>> @@ -0,0 +1,26 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/*
>> + * Based on arch/arm64/include/asm/probes.h
>> + *
>> + * Copyright (C) 2013 Linaro Limited
>> + */
>> +#ifndef _RISCV_PROBES_H
>> +#define _RISCV_PROBES_H
>> +
>> +typedef u32 probe_opcode_t;
>> +typedef void (probes_handler_t) (u32 opcode, long addr, struct pt_regs *);
>> +
>> +/* architecture specific copy of original instruction */
>> +struct arch_probe_insn {
>> +	probes_handler_t *handler;
>> +	/* restore address after simulation */
>> +	unsigned long restore;
>> +};
>> +#ifdef CONFIG_KPROBES
>> +typedef u32 kprobe_opcode_t;
>> +struct arch_specific_insn {
>> +	struct arch_probe_insn api;
>> +};
>> +#endif
> 
> Are there any reason of putting this kprobes dedicated data structure here?

No, this is from the arm64 implementation as they share the instruction
decoding with uprobes. Forgot to clean that up.

> 
>> +
>> +#endif /* _RISCV_PROBES_H */
>> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
>> index f13f7f276639..5360a445b9d3 100644
>> --- a/arch/riscv/kernel/Makefile
>> +++ b/arch/riscv/kernel/Makefile
>> @@ -28,6 +28,7 @@ obj-y	+= stacktrace.o
>>  obj-y	+= vdso.o
>>  obj-y	+= cacheinfo.o
>>  obj-y	+= vdso/
>> +obj-y	+= probes/
>>  
>>  CFLAGS_setup.o := -mcmodel=medany
>>  
>> diff --git a/arch/riscv/kernel/probes/Makefile b/arch/riscv/kernel/probes/Makefile
>> new file mode 100644
>> index 000000000000..144d1c1743fb
>> --- /dev/null
>> +++ b/arch/riscv/kernel/probes/Makefile
>> @@ -0,0 +1,3 @@
>> +# SPDX-License-Identifier: GPL-2.0
>> +obj-$(CONFIG_KPROBES)		+= kprobes.o kprobes_trampoline.o \
>> +				   decode-insn.o simulate-insn.o
>> diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c
>> new file mode 100644
>> index 000000000000..2d8f46f4c2e7
>> --- /dev/null
>> +++ b/arch/riscv/kernel/probes/decode-insn.c
>> @@ -0,0 +1,38 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>> +
>> +#include <linux/kernel.h>
>> +#include <linux/kprobes.h>
>> +#include <linux/module.h>
>> +#include <linux/kallsyms.h>
>> +#include <asm/sections.h>
>> +
>> +#include "decode-insn.h"
>> +#include "simulate-insn.h"
>> +
>> +#define C_ADDISP16_MASK 0x6F83
>> +#define C_ADDISP16_VAL  0x6101
>> +
>> +/* Return:
>> + *   INSN_REJECTED     If instruction is one not allowed to kprobe,
>> + *   INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot.
>> + */
>> +enum probe_insn __kprobes
>> +riscv_probe_decode_insn(kprobe_opcode_t *addr, struct arch_probe_insn *api)
> 
> Please don't use __kprobes anymore. That is old stlye, instead, please
> use NOKPROBE_SYMBOL() or nokprobe_inline for static-inline function.
> (NOKPROBE_SYMBOL() will make the symbol non-inline always)

OK, should I make a note to change that in the arm64 port as well in a
separate patch?

> 
>> +{
>> +	probe_opcode_t insn = le32_to_cpu(*addr);
>> +
>> +	if (!is_compressed_insn(insn)) {
>> +		pr_warn("Can't handle non-compressed instruction %x\n", insn);
>> +		return INSN_REJECTED;
>> +	}
>> +
>> +	/* c.addisp16 imm */
>> +	if ((insn & C_ADDISP16_MASK) == C_ADDISP16_VAL) {
>> +		api->handler = simulate_caddisp16;
>> +	} else {
>> +		pr_warn("Rejected unknown instruction %x\n", insn);
>> +		return INSN_REJECTED;
>> +	}
>> +
>> +	return INSN_GOOD_NO_SLOT;
>> +}
>> diff --git a/arch/riscv/kernel/probes/decode-insn.h b/arch/riscv/kernel/probes/decode-insn.h
>> new file mode 100644
>> index 000000000000..0053ed6a308a
>> --- /dev/null
>> +++ b/arch/riscv/kernel/probes/decode-insn.h
>> @@ -0,0 +1,23 @@
>> +/* SPDX-License-Identifier: GPL-2.0+ */
>> +#ifndef _RISCV_KERNEL_KPROBES_DECODE_INSN_H
>> +#define _RISCV_KERNEL_KPROBES_DECODE_INSN_H
>> +
>> +#include <asm/sections.h>
>> +#include <asm/kprobes.h>
>> +
>> +enum probe_insn {
>> +	INSN_REJECTED,
>> +	INSN_GOOD_NO_SLOT,
>> +};
>> +
>> +/*
>> + * Compressed instruction format:
>> + * xxxxxxxxxxxxxxaa where aa != 11
>> + */
>> +#define is_compressed_insn(insn) ((insn & 0x3) != 0x3)
>> +
>> +#ifdef CONFIG_KPROBES
>> +enum probe_insn __kprobes
>> +riscv_probe_decode_insn(kprobe_opcode_t *addr, struct arch_probe_insn *asi);
>> +#endif
>> +#endif /* _RISCV_KERNEL_KPROBES_DECODE_INSN_H */
>> diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
>> new file mode 100644
>> index 000000000000..3c7b5cf72ee1
>> --- /dev/null
>> +++ b/arch/riscv/kernel/probes/kprobes.c
>> @@ -0,0 +1,401 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>> +
>> +/*
>> + * Kprobes support for RISC-V
>> + *
>> + * Author: Patrick St?hlin <me@packi.ch>
>> + */
>> +#include <linux/kprobes.h>
>> +#include <linux/extable.h>
>> +#include <linux/slab.h>
>> +#include <asm/ptrace.h>
>> +#include <linux/uaccess.h>
>> +#include <asm/sections.h>
>> +
>> +#include "decode-insn.h"
>> +
>> +DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
>> +DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
>> +
>> +static void __kprobes
>> +post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
>> +
>> +static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
>> +{
>> +	if (is_compressed_insn(opcode))
>> +		*(u16 *)addr = cpu_to_le16(opcode);
>> +	else
>> +		*addr = cpu_to_le32(opcode);
>> +
>> +	return 0;
>> +}
>> +
>> +static void __kprobes arch_prepare_simulate(struct kprobe *p)
>> +{
>> +	unsigned long offset = is_compressed_insn(p->opcode) ? 2 : 4;
>> +
>> +	p->ainsn.api.restore = (unsigned long)p->addr + offset;
>> +}
>> +
>> +static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
>> +{
>> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
>> +
>> +	if (p->ainsn.api.handler)
>> +		p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);
> 
> it seems api.handler must be here, 

true

> 
>> +
>> +	/* single instruction simulated, now go for post processing */
>> +	post_kprobe_handler(kcb, regs);
>> +}
>> +
>> +int __kprobes arch_prepare_kprobe(struct kprobe *p)
>> +{
>> +	unsigned long probe_addr = (unsigned long)p->addr;
>> +	extern char __start_rodata[];
>> +	extern char __end_rodata[];
>> +
>> +	if (probe_addr & 0x1) {
>> +		pr_warn("Address not aligned.\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	/* copy instruction */
>> +	p->opcode = le32_to_cpu(*p->addr);
>> +
>> +	if (probe_addr >= (unsigned long) __start_rodata &&
>> +	    probe_addr <= (unsigned long) __end_rodata) {
>> +		return -EINVAL;
>> +	}
>> +
>> +	/* decode instruction */
>> +	switch (riscv_probe_decode_insn(p->addr, &p->ainsn.api)) {
>> +	case INSN_REJECTED:	/* insn not supported */
>> +		return -EINVAL;
>> +
>> +	case INSN_GOOD_NO_SLOT:	/* insn needs simulation */
>> +		break;
>> +	}
>> +
>> +	arch_prepare_simulate(p);
>> +
>> +	return 0;
>> +}
>> +
>> +#define C_EBREAK_OPCODE 0x9002
>> +
>> +/* arm kprobe: install breakpoint in text */
>> +void __kprobes arch_arm_kprobe(struct kprobe *p)
>> +{
>> +	patch_text(p->addr, C_EBREAK_OPCODE);
>> +}
>> +
>> +/* disarm kprobe: remove breakpoint from text */
>> +void __kprobes arch_disarm_kprobe(struct kprobe *p)
>> +{
>> +	patch_text(p->addr, p->opcode);
>> +}
>> +
>> +void __kprobes arch_remove_kprobe(struct kprobe *p)
>> +{
>> +}
>> +
>> +static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
>> +{
>> +	kcb->prev_kprobe.kp = kprobe_running();
>> +	kcb->prev_kprobe.status = kcb->kprobe_status;
>> +}
>> +
>> +static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
>> +{
>> +	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
>> +	kcb->kprobe_status = kcb->prev_kprobe.status;
>> +}
>> +
>> +static void __kprobes set_current_kprobe(struct kprobe *p)
>> +{
>> +	__this_cpu_write(current_kprobe, p);
>> +}
>> +
>> +static void __kprobes simulate(struct kprobe *p,
>> +			       struct pt_regs *regs,
>> +			       struct kprobe_ctlblk *kcb, int reenter)
>> +{
>> +	if (reenter) {
>> +		save_previous_kprobe(kcb);
>> +		set_current_kprobe(p);
>> +		kcb->kprobe_status = KPROBE_REENTER;
>> +	} else {
>> +		kcb->kprobe_status = KPROBE_HIT_SS;
>> +	}
>> +
>> +	arch_simulate_insn(p, regs);
>> +}
>> +
>> +static int __kprobes reenter_kprobe(struct kprobe *p,
>> +				    struct pt_regs *regs,
>> +				    struct kprobe_ctlblk *kcb)
>> +{
>> +	switch (kcb->kprobe_status) {
>> +	case KPROBE_HIT_SSDONE:
>> +	case KPROBE_HIT_ACTIVE:
>> +		kprobes_inc_nmissed_count(p);
>> +		simulate(p, regs, kcb, 1);
>> +		break;
>> +	case KPROBE_HIT_SS:
>> +	case KPROBE_REENTER:
>> +		pr_warn("Unrecoverable kprobe detected.\n");
>> +		dump_kprobe(p);
>> +		BUG();
>> +		break;
>> +	default:
>> +		WARN_ON(1);
>> +		return 0;
>> +	}
>> +
>> +	return 1;
> 
> If this always return 1, we can make it void return.

Agreed, I'll change that.

> 
>> +}
>> +
>> +static void __kprobes
>> +post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
>> +{
>> +	struct kprobe *cur = kprobe_running();
>> +
>> +	if (!cur)
>> +		return;
>> +
>> +	/* return addr restore if non-branching insn */
>> +	if (cur->ainsn.api.restore != 0)
>> +		instruction_pointer_set(regs, cur->ainsn.api.restore);
>> +
>> +	/* restore back original saved kprobe variables and continue */
>> +	if (kcb->kprobe_status == KPROBE_REENTER) {
>> +		restore_previous_kprobe(kcb);
>> +		return;
>> +	}
>> +	/* call post handler */
>> +	kcb->kprobe_status = KPROBE_HIT_SSDONE;
>> +	if (cur->post_handler)	{
>> +		/* post_handler can hit breakpoint and single step
>> +		 * again, so we enable D-flag for recursive exception.
>> +		 */
>> +		cur->post_handler(cur, regs, 0);
>> +	}
>> +
>> +	reset_current_kprobe();
>> +}
>> +
>> +int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int cause)
>> +{
>> +	struct kprobe *cur = kprobe_running();
>> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
>> +
>> +	switch (kcb->kprobe_status) {
>> +	case KPROBE_HIT_SS:
>> +	case KPROBE_REENTER:
>> +		/*
>> +		 * We are here because the instruction being single
>> +		 * stepped caused a page fault. We reset the current
>> +		 * kprobe and the ip points back to the probe address
>> +		 * and allow the page fault handler to continue as a
>> +		 * normal page fault.
>> +		 */
>> +		instruction_pointer_set(regs, (unsigned long) cur->addr);
>> +		if (!instruction_pointer(regs))
>> +			BUG();
> 
> Use BUG_ON().

OK

> 
>> +
>> +		if (kcb->kprobe_status == KPROBE_REENTER)
>> +			restore_previous_kprobe(kcb);
>> +		else
>> +			reset_current_kprobe();
>> +
>> +		break;
>> +	case KPROBE_HIT_ACTIVE:
>> +	case KPROBE_HIT_SSDONE:
>> +		/*
>> +		 * We increment the nmissed count for accounting,
>> +		 * we can also use npre/npostfault count for accounting
>> +		 * these specific fault cases.
>> +		 */
>> +		kprobes_inc_nmissed_count(cur);
>> +
>> +		/*
>> +		 * We come here because instructions in the pre/post
>> +		 * handler caused the page_fault, this could happen
>> +		 * if handler tries to access user space by
>> +		 * copy_from_user(), get_user() etc. Let the
>> +		 * user-specified handler try to fix it first.
>> +		 */
>> +		if (cur->fault_handler && cur->fault_handler(cur, regs, cause))
>> +			return 1;
>> +
>> +		/*
>> +		 * In case the user-specified fault handler returned
>> +		 * zero, try to fix up.
>> +		 */
>> +		if (fixup_exception(regs))
>> +			return 1;
>> +	}
>> +	return 0;
>> +}
>> +
>> +static void __kprobes kprobe_handler(struct pt_regs *regs)
>> +{
> 
> Does this handler run under local IRQ disabled? (for making sure)

Exceptions are being handled with locals IRQs _enabled_. As we've not
implemented any simulated instructions to modify the instruction
pointer, I think this is safe? Then again, I'm new to this, so please
bear with me.

> 
>> +	struct kprobe *p, *cur_kprobe;
>> +	struct kprobe_ctlblk *kcb;
>> +	unsigned long addr = instruction_pointer(regs);
>> +
>> +	kcb = get_kprobe_ctlblk();
>> +	cur_kprobe = kprobe_running();
>> +
>> +	p = get_kprobe((kprobe_opcode_t *) addr);
>> +
>> +	if (p) {
>> +		if (cur_kprobe) {
>> +			if (reenter_kprobe(p, regs, kcb))
>> +				return;
>> +		} else {
>> +			/* Probe hit */
>> +			set_current_kprobe(p);
>> +			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
>> +
>> +			/*
>> +			 * If we have no pre-handler or it returned 0, we
>> +			 * continue with normal processing.  If we have a
>> +			 * pre-handler and it returned non-zero, it will
>> +			 * modify the execution path and no need to single
>> +			 * stepping. Let's just reset current kprobe and exit.
>> +			 *
>> +			 * pre_handler can hit a breakpoint and can step thru
>> +			 * before return, keep PSTATE D-flag enabled until
>> +			 * pre_handler return back.
> 
> Is this true on RISC-V too?

It's not as we don't have a debug-unit at the moment. I'll remove the
second part of the comment block.

> 
>> +			 */
>> +			if (!p->pre_handler || !p->pre_handler(p, regs))
>> +				simulate(p, regs, kcb, 0);
>> +			else
>> +				reset_current_kprobe();
>> +		}
>> +	}
>> +	/*
>> +	 * The breakpoint instruction was removed right
>> +	 * after we hit it.  Another cpu has removed
>> +	 * either a probepoint or a debugger breakpoint
>> +	 * at this address.  In either case, no further
>> +	 * handling of this interrupt is appropriate.
>> +	 * Return back to original instruction, and continue.
>> +	 */
> 
> This should return 0 if it doesn't handle anything, but if it handles c.break
> should return 1.

I thought so too, but didn't insert one because of the comment (again,
copied from arm64). If get_kprobe doesn't return a result, it could have
been removed between the time the exception got raised or is the comment
just wrong? On the other hand, solving it this way effectively means
that we'll silently drop any other exceptions.

>> +}
>> +
>> +int __kprobes
>> +kprobe_breakpoint_handler(struct pt_regs *regs)
>> +{
>> +	kprobe_handler(regs);
>> +	return 1;
> 
> Why don't you call kprobe_handler directly?

I should.

> 
>> +}
>> +
>> +bool arch_within_kprobe_blacklist(unsigned long addr)
>> +{
>> +	if ((addr >= (unsigned long)__kprobes_text_start &&
>> +	    addr < (unsigned long)__kprobes_text_end) ||
>> +	    (addr >= (unsigned long)__entry_text_start &&
>> +	    addr < (unsigned long)__entry_text_end) ||
>> +	    !!search_exception_tables(addr))
>> +		return true;
>> +
>> +	return false;
>> +}
>> +
>> +void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
>> +{
>> +	struct kretprobe_instance *ri = NULL;
>> +	struct hlist_head *head, empty_rp;
>> +	struct hlist_node *tmp;
>> +	unsigned long flags, orig_ret_address = 0;
>> +	unsigned long trampoline_address =
>> +		(unsigned long)&kretprobe_trampoline;
>> +	kprobe_opcode_t *correct_ret_addr = NULL;
>> +
> 
> 	It seems you don't setup instruction_pointer.

I don't think I get what you mean by that. The instruction pointer (or
rather the return address register) gets set by kretprobe_trampoline.S
to the address returned from this function.

> 
>> +	INIT_HLIST_HEAD(&empty_rp);
>> +	kretprobe_hash_lock(current, &head, &flags);
>> +
>> +	/*
>> +	 * It is possible to have multiple instances associated with a given
>> +	 * task either because multiple functions in the call path have
>> +	 * return probes installed on them, and/or more than one
>> +	 * return probe was registered for a target function.
>> +	 *
>> +	 * We can handle this because:
>> +	 *     - instances are always pushed into the head of the list
>> +	 *     - when multiple return probes are registered for the same
>> +	 *	 function, the (chronologically) first instance's ret_addr
>> +	 *	 will be the real return address, and all the rest will
>> +	 *	 point to kretprobe_trampoline.
>> +	 */
>> +	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
>> +		if (ri->task != current)
>> +			/* another task is sharing our hash bucket */
>> +			continue;
>> +
>> +		orig_ret_address = (unsigned long)ri->ret_addr;
>> +
>> +		if (orig_ret_address != trampoline_address)
>> +			/*
>> +			 * This is the real return address. Any other
>> +			 * instances associated with this task are for
>> +			 * other calls deeper on the call stack
>> +			 */
>> +			break;
>> +	}
>> +
>> +	kretprobe_assert(ri, orig_ret_address, trampoline_address);
>> +
>> +	correct_ret_addr = ri->ret_addr;
>> +	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
>> +		if (ri->task != current)
>> +			/* another task is sharing our hash bucket */
>> +			continue;
>> +
>> +		orig_ret_address = (unsigned long)ri->ret_addr;
>> +		if (ri->rp && ri->rp->handler) {
>> +			__this_cpu_write(current_kprobe, &ri->rp->kp);
>> +			get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
>> +			ri->ret_addr = correct_ret_addr;
>> +			ri->rp->handler(ri, regs);
>> +			__this_cpu_write(current_kprobe, NULL);
>> +		}
>> +
>> +		recycle_rp_inst(ri, &empty_rp);
>> +
>> +		if (orig_ret_address != trampoline_address)
>> +			/*
>> +			 * This is the real return address. Any other
>> +			 * instances associated with this task are for
>> +			 * other calls deeper on the call stack
>> +			 */
>> +			break;
>> +	}
>> +
>> +	kretprobe_hash_unlock(current, &flags);
>> +
>> +	hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
>> +		hlist_del(&ri->hlist);
>> +		kfree(ri);
>> +	}
>> +	return (void *)orig_ret_address;
>> +}
>> +
>> +void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
>> +				      struct pt_regs *regs)
>> +{
>> +	ri->ret_addr = (kprobe_opcode_t *)regs->ra;
>> +	regs->ra = (long)&kretprobe_trampoline;
>> +}
>> +
>> +int __kprobes arch_trampoline_kprobe(struct kprobe *p)
>> +{
>> +	return 0;
>> +}
>> +
>> +int __init arch_init_kprobes(void)
>> +{
>> +	return 0;
>> +}
>> diff --git a/arch/riscv/kernel/probes/kprobes_trampoline.S b/arch/riscv/kernel/probes/kprobes_trampoline.S
>> new file mode 100644
>> index 000000000000..c7ceda9556a3
>> --- /dev/null
>> +++ b/arch/riscv/kernel/probes/kprobes_trampoline.S
>> @@ -0,0 +1,91 @@
>> +/* SPDX-License-Identifier: GPL-2.0+ */
>> +
>> +#include <linux/linkage.h>
>> +
>> +#include <asm/asm.h>
>> +#include <asm/asm-offsets.h>
>> +
>> +	.text
>> +	.altmacro
>> +
>> +	.macro save_all_base_regs
>> +	REG_S x1,  PT_RA(sp)
>> +	REG_S x3,  PT_GP(sp)
>> +	REG_S x4,  PT_TP(sp)
>> +	REG_S x5,  PT_T0(sp)
>> +	REG_S x6,  PT_T1(sp)
>> +	REG_S x7,  PT_T2(sp)
>> +	REG_S x8,  PT_S0(sp)
>> +	REG_S x9,  PT_S1(sp)
>> +	REG_S x10, PT_A0(sp)
>> +	REG_S x11, PT_A1(sp)
>> +	REG_S x12, PT_A2(sp)
>> +	REG_S x13, PT_A3(sp)
>> +	REG_S x14, PT_A4(sp)
>> +	REG_S x15, PT_A5(sp)
>> +	REG_S x16, PT_A6(sp)
>> +	REG_S x17, PT_A7(sp)
>> +	REG_S x18, PT_S2(sp)
>> +	REG_S x19, PT_S3(sp)
>> +	REG_S x20, PT_S4(sp)
>> +	REG_S x21, PT_S5(sp)
>> +	REG_S x22, PT_S6(sp)
>> +	REG_S x23, PT_S7(sp)
>> +	REG_S x24, PT_S8(sp)
>> +	REG_S x25, PT_S9(sp)
>> +	REG_S x26, PT_S10(sp)
>> +	REG_S x27, PT_S11(sp)
>> +	REG_S x28, PT_T3(sp)
>> +	REG_S x29, PT_T4(sp)
>> +	REG_S x30, PT_T5(sp)
>> +	REG_S x31, PT_T6(sp)
>> +	.endm
>> +
>> +	.macro restore_all_base_regs
>> +	REG_L x3,  PT_GP(sp)
>> +	REG_L x4,  PT_TP(sp)
>> +	REG_L x5,  PT_T0(sp)
>> +	REG_L x6,  PT_T1(sp)
>> +	REG_L x7,  PT_T2(sp)
>> +	REG_L x8,  PT_S0(sp)
>> +	REG_L x9,  PT_S1(sp)
>> +	REG_L x10, PT_A0(sp)
>> +	REG_L x11, PT_A1(sp)
>> +	REG_L x12, PT_A2(sp)
>> +	REG_L x13, PT_A3(sp)
>> +	REG_L x14, PT_A4(sp)
>> +	REG_L x15, PT_A5(sp)
>> +	REG_L x16, PT_A6(sp)
>> +	REG_L x17, PT_A7(sp)
>> +	REG_L x18, PT_S2(sp)
>> +	REG_L x19, PT_S3(sp)
>> +	REG_L x20, PT_S4(sp)
>> +	REG_L x21, PT_S5(sp)
>> +	REG_L x22, PT_S6(sp)
>> +	REG_L x23, PT_S7(sp)
>> +	REG_L x24, PT_S8(sp)
>> +	REG_L x25, PT_S9(sp)
>> +	REG_L x26, PT_S10(sp)
>> +	REG_L x27, PT_S11(sp)
>> +	REG_L x28, PT_T3(sp)
>> +	REG_L x29, PT_T4(sp)
>> +	REG_L x30, PT_T5(sp)
>> +	REG_L x31, PT_T6(sp)
>> +	.endm
>> +
>> +ENTRY(kretprobe_trampoline)
>> +	addi sp, sp, -(PT_SIZE_ON_STACK)
>> +	save_all_base_regs
>> +
>> +	move a0, sp /* pt_regs */
>> +
>> +	call trampoline_probe_handler
>> +
>> +	/* use the result as the return-address */
>> +	move ra, a0
>> +
>> +	restore_all_base_regs
>> +	addi sp, sp, PT_SIZE_ON_STACK
>> +
>> +	ret
>> +ENDPROC(kretprobe_trampoline)
>> diff --git a/arch/riscv/kernel/probes/simulate-insn.c b/arch/riscv/kernel/probes/simulate-insn.c
>> new file mode 100644
>> index 000000000000..5734d9bae22f
>> --- /dev/null
>> +++ b/arch/riscv/kernel/probes/simulate-insn.c
>> @@ -0,0 +1,33 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>> +
>> +#include <linux/bitops.h>
>> +#include <linux/kernel.h>
>> +#include <linux/kprobes.h>
>> +
>> +#include "simulate-insn.h"
>> +
>> +#define bit_at(value, bit)		((value) & (1 << (bit)))
>> +#define move_bit_at(value, bit, to)	((bit_at(value, bit) >> bit) << to)
>> +
>> +void __kprobes
>> +simulate_caddisp16(u32 opcode, long addr, struct pt_regs *regs)
>> +{
>> +	s16 imm;
>> +
>> +	/*
>> +	 * Immediate value layout in c.addisp16:
>> +	 * xxx9 xxxx x468 75xx
>> +	 * 1  1    8    4    0
>> +	 * 5  2
>> +	 */
>> +	imm = sign_extend32(
>> +		move_bit_at(opcode, 12, 9) |
>> +		move_bit_at(opcode, 6, 4) |
>> +		move_bit_at(opcode, 5, 6) |
>> +		move_bit_at(opcode, 4, 8) |
>> +		move_bit_at(opcode, 3, 7) |
>> +		move_bit_at(opcode, 2, 5),
>> +		9);
>> +
>> +	regs->sp += imm;
> 
> What about updating regs->sepc?

sepc gets updated by instruction_pointer_set in kprobe_handler

> 
>> +}
>> diff --git a/arch/riscv/kernel/probes/simulate-insn.h b/arch/riscv/kernel/probes/simulate-insn.h
>> new file mode 100644
>> index 000000000000..dc2c06c30167
>> --- /dev/null
>> +++ b/arch/riscv/kernel/probes/simulate-insn.h
>> @@ -0,0 +1,8 @@
>> +/* SPDX-License-Identifier: GPL-2.0+ */
>> +
>> +#ifndef _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H
>> +#define _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H
>> +
>> +void simulate_caddisp16(u32 opcode, long addr, struct pt_regs *regs);
>> +
>> +#endif /* _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H */
>> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
>> index 24a9333dda2c..d7113178d401 100644
>> --- a/arch/riscv/kernel/traps.c
>> +++ b/arch/riscv/kernel/traps.c
>> @@ -18,6 +18,7 @@
>>  #include <linux/sched/signal.h>
>>  #include <linux/signal.h>
>>  #include <linux/kdebug.h>
>> +#include <linux/kprobes.h>
>>  #include <linux/uaccess.h>
>>  #include <linux/mm.h>
>>  #include <linux/module.h>
>> @@ -120,8 +121,14 @@ DO_ERROR_INFO(do_trap_ecall_m,
>>  
>>  asmlinkage void do_trap_break(struct pt_regs *regs)
>>  {
>> +	bool handler_found = false;
>> +
>> +#ifdef CONFIG_KPROBES
>> +	if (kprobe_breakpoint_handler(regs))
>> +		handler_found = 1;
> 
> Why don't you just return from here?

Following the pattern I've seen in other places, I can change that.

> 
>> +#endif
>>  #ifdef CONFIG_GENERIC_BUG
>> -	if (!user_mode(regs)) {
>> +	if (!handler_found && !user_mode(regs)) {
>>  		enum bug_trap_type type;
>>  
>>  		type = report_bug(regs->sepc, regs);
>> @@ -137,7 +144,9 @@ asmlinkage void do_trap_break(struct pt_regs *regs)
>>  	}
>>  #endif /* CONFIG_GENERIC_BUG */
>>  
>> -	force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)(regs->sepc), current);
>> +	if (!handler_found)
>> +		force_sig_fault(SIGTRAP, TRAP_BRKPT,
>> +			(void __user *)(regs->sepc), current);
>>  }
>>  
>>  #ifdef CONFIG_GENERIC_BUG
>> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
>> index 88401d5125bc..eff816e33479 100644
>> --- a/arch/riscv/mm/fault.c
>> +++ b/arch/riscv/mm/fault.c
>> @@ -22,6 +22,7 @@
>>  
>>  #include <linux/mm.h>
>>  #include <linux/kernel.h>
>> +#include <linux/kprobes.h>
>>  #include <linux/interrupt.h>
>>  #include <linux/perf_event.h>
>>  #include <linux/signal.h>
>> @@ -30,11 +31,33 @@
>>  #include <asm/pgalloc.h>
>>  #include <asm/ptrace.h>
>>  
>> +#ifdef CONFIG_KPROBES
>> +static inline int notify_page_fault(struct pt_regs *regs, unsigned int cause)
> 
> please use nokprobe_inline.

OK.

> 
>> +{
>> +	int ret = 0;
>> +
>> +	/* kprobe_running() needs smp_processor_id() */
>> +	if (!user_mode(regs)) {
>> +		preempt_disable();
>> +		if (kprobe_running() && kprobe_fault_handler(regs, cause))
>> +			ret = 1;
>> +		preempt_enable();
>> +	}
>> +
>> +	return ret;
>> +}
>> +#else
>> +static inline int notify_page_fault(struct pt_regs *regs, unsigned int cause)
>> +{
>> +	return 0;
>> +}
>> +#endif
>> +
>>  /*
>>   * This routine handles page faults.  It determines the address and the
>>   * problem, and then passes it off to one of the appropriate routines.
>>   */
>> -asmlinkage void do_page_fault(struct pt_regs *regs)
>> +asmlinkage void __kprobes do_page_fault(struct pt_regs *regs)
>>  {
>>  	struct task_struct *tsk;
>>  	struct vm_area_struct *vma;
>> @@ -47,6 +70,9 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
>>  	cause = regs->scause;
>>  	addr = regs->sbadaddr;
>>  
>> +	if (notify_page_fault(regs, cause))
>> +		return;
>> +
>>  	tsk = current;
>>  	mm = tsk->mm;
>>  
>> -- 
>> 2.17.1
>>
> 
> Thank you,
> 

^ permalink raw reply	[flat|nested] 18+ messages in thread

* Re: [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support
  2018-11-14 20:52     ` me
@ 2018-11-14 20:52       ` Patrick Staehlin
  2018-11-15  8:41       ` mhiramat
  1 sibling, 0 replies; 18+ messages in thread
From: Patrick Staehlin @ 2018-11-14 20:52 UTC (permalink / raw)
  To: Masami Hiramatsu
  Cc: Albert Ou, Anders Roxell, Andrew Morton, Alan Kao,
	Catalin Marinas, Palmer Dabbelt, Will Deacon, linux-kernel,
	Al Viro, Souptick Joarder, Zong Li, Thomas Gleixner,
	Eric W. Biederman, linux-riscv, zhong jiang, Ingo Molnar,
	Luc Van Oostenryck, Jim Wilson

Hi Masami,

thank you for your remarks.

On 14.11.18 09:37, Masami Hiramatsu wrote>
> Thank you very much for implementing kprobes on RISC-V :)
> 
> On Tue, 13 Nov 2018 20:58:04 +0100
> Patrick Stählin <me@packi.ch> wrote:
> 
>> First implementation, adapted from arm64. The C.ADDISP16 instruction
>> gets simulated and the kprobes-handler called by inserting a C.EBREAK
>> instruction.
>>
>> C.ADDISP16 was chosen as it sets-up the stack frame for functions.
>> Some work has been done to support probes on non-compressed
>> instructions but there is no support yet for decoding those.
> 
> Does this only support C.ADDISP16? No other insns are supported?
> Supporting 1 insn is too few I think.

At the moment, yes. I'm waiting for some input from somebody with deeper
insights into the RISC-V architecture than me before implementing more
instructions, should solution I've chosen be woefully inadequate.

> Can RISC-V do single stepping? If not, we need to prepare emulator
> as match as possible, or for ALU instructions, we can run it on
> buffer and hook it.

The debug-specification is still a draft but there are some softcores
that implement it. But even if it was finalized I don't think this will
be made a mandatory extension so we need to simulate/emulate a good part
of the instruction set anyway.

>> The way forward should be to uncompress the instructions for simulation
>> to reduce the number of instructions used to decode  the immediate
>> values on probe hit.
> 
> I have some comments on the patch, please review.
> 
>>
>> Signed-off-by: Patrick Stählin <me@packi.ch>
>> ---
>>  arch/riscv/Kconfig                            |   5 +-
>>  arch/riscv/include/asm/kprobes.h              |  30 ++
>>  arch/riscv/include/asm/probes.h               |  26 ++
>>  arch/riscv/kernel/Makefile                    |   1 +
>>  arch/riscv/kernel/probes/Makefile             |   3 +
>>  arch/riscv/kernel/probes/decode-insn.c        |  38 ++
>>  arch/riscv/kernel/probes/decode-insn.h        |  23 +
>>  arch/riscv/kernel/probes/kprobes.c            | 401 ++++++++++++++++++
>>  arch/riscv/kernel/probes/kprobes_trampoline.S |  91 ++++
>>  arch/riscv/kernel/probes/simulate-insn.c      |  33 ++
>>  arch/riscv/kernel/probes/simulate-insn.h      |   8 +
>>  arch/riscv/kernel/traps.c                     |  13 +-
>>  arch/riscv/mm/fault.c                         |  28 +-
>>  13 files changed, 694 insertions(+), 6 deletions(-)
>>  create mode 100644 arch/riscv/include/asm/probes.h
>>  create mode 100644 arch/riscv/kernel/probes/Makefile
>>  create mode 100644 arch/riscv/kernel/probes/decode-insn.c
>>  create mode 100644 arch/riscv/kernel/probes/decode-insn.h
>>  create mode 100644 arch/riscv/kernel/probes/kprobes.c
>>  create mode 100644 arch/riscv/kernel/probes/kprobes_trampoline.S
>>  create mode 100644 arch/riscv/kernel/probes/simulate-insn.c
>>  create mode 100644 arch/riscv/kernel/probes/simulate-insn.h
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index b157ac82d486..11ef4030e8f2 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -44,6 +44,8 @@ config RISCV
>>  	select GENERIC_IRQ_MULTI_HANDLER
>>  	select ARCH_HAS_PTE_SPECIAL
>>  	select HAVE_REGS_AND_STACK_ACCESS_API
>> +	select HAVE_KPROBES
>> +	select HAVE_KRETPROBES
>>  
>>  config MMU
>>  	def_bool y
>> @@ -89,9 +91,6 @@ config PGTABLE_LEVELS
>>  	default 3 if 64BIT
>>  	default 2
>>  
>> -config HAVE_KPROBES
>> -	def_bool n
>> -
>>  menu "Platform type"
>>  
>>  choice
>> diff --git a/arch/riscv/include/asm/kprobes.h b/arch/riscv/include/asm/kprobes.h
>> index c7eb010d1528..657adcd35a3d 100644
>> --- a/arch/riscv/include/asm/kprobes.h
>> +++ b/arch/riscv/include/asm/kprobes.h
>> @@ -19,4 +19,34 @@
>>  
>>  #include <asm-generic/kprobes.h>
>>  
>> +#ifdef CONFIG_KPROBES
>> +#include <linux/types.h>
>> +#include <linux/ptrace.h>
>> +#include <linux/percpu.h>
>> +
>> +#define flush_insn_slot(p)		do { } while (0)
>> +#define kretprobe_blacklist_size	0
>> +
>> +#include <asm/probes.h>
>> +
>> +struct prev_kprobe {
>> +	struct kprobe *kp;
>> +	unsigned int status;
>> +};
>> +
>> +/* per-cpu kprobe control block */
>> +struct kprobe_ctlblk {
>> +	unsigned int kprobe_status;
>> +	struct prev_kprobe prev_kprobe;
>> +};
>> +
>> +void arch_remove_kprobe(struct kprobe *p);
>> +int kprobe_fault_handler(struct pt_regs *regs, unsigned int cause);
>> +int kprobe_exceptions_notify(struct notifier_block *self,
>> +			     unsigned long val, void *data);
>> +int kprobe_breakpoint_handler(struct pt_regs *regs);
>> +void kretprobe_trampoline(void);
>> +void __kprobes *trampoline_probe_handler(struct pt_regs *regs);
>> +
>> +#endif /* CONFIG_KPROBES */
>>  #endif /* _RISCV_KPROBES_H */
>> diff --git a/arch/riscv/include/asm/probes.h b/arch/riscv/include/asm/probes.h
>> new file mode 100644
>> index 000000000000..64cf12567539
>> --- /dev/null
>> +++ b/arch/riscv/include/asm/probes.h
>> @@ -0,0 +1,26 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/*
>> + * Based on arch/arm64/include/asm/probes.h
>> + *
>> + * Copyright (C) 2013 Linaro Limited
>> + */
>> +#ifndef _RISCV_PROBES_H
>> +#define _RISCV_PROBES_H
>> +
>> +typedef u32 probe_opcode_t;
>> +typedef void (probes_handler_t) (u32 opcode, long addr, struct pt_regs *);
>> +
>> +/* architecture specific copy of original instruction */
>> +struct arch_probe_insn {
>> +	probes_handler_t *handler;
>> +	/* restore address after simulation */
>> +	unsigned long restore;
>> +};
>> +#ifdef CONFIG_KPROBES
>> +typedef u32 kprobe_opcode_t;
>> +struct arch_specific_insn {
>> +	struct arch_probe_insn api;
>> +};
>> +#endif
> 
> Are there any reason of putting this kprobes dedicated data structure here?

No, this is from the arm64 implementation as they share the instruction
decoding with uprobes. Forgot to clean that up.

> 
>> +
>> +#endif /* _RISCV_PROBES_H */
>> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
>> index f13f7f276639..5360a445b9d3 100644
>> --- a/arch/riscv/kernel/Makefile
>> +++ b/arch/riscv/kernel/Makefile
>> @@ -28,6 +28,7 @@ obj-y	+= stacktrace.o
>>  obj-y	+= vdso.o
>>  obj-y	+= cacheinfo.o
>>  obj-y	+= vdso/
>> +obj-y	+= probes/
>>  
>>  CFLAGS_setup.o := -mcmodel=medany
>>  
>> diff --git a/arch/riscv/kernel/probes/Makefile b/arch/riscv/kernel/probes/Makefile
>> new file mode 100644
>> index 000000000000..144d1c1743fb
>> --- /dev/null
>> +++ b/arch/riscv/kernel/probes/Makefile
>> @@ -0,0 +1,3 @@
>> +# SPDX-License-Identifier: GPL-2.0
>> +obj-$(CONFIG_KPROBES)		+= kprobes.o kprobes_trampoline.o \
>> +				   decode-insn.o simulate-insn.o
>> diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c
>> new file mode 100644
>> index 000000000000..2d8f46f4c2e7
>> --- /dev/null
>> +++ b/arch/riscv/kernel/probes/decode-insn.c
>> @@ -0,0 +1,38 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>> +
>> +#include <linux/kernel.h>
>> +#include <linux/kprobes.h>
>> +#include <linux/module.h>
>> +#include <linux/kallsyms.h>
>> +#include <asm/sections.h>
>> +
>> +#include "decode-insn.h"
>> +#include "simulate-insn.h"
>> +
>> +#define C_ADDISP16_MASK 0x6F83
>> +#define C_ADDISP16_VAL  0x6101
>> +
>> +/* Return:
>> + *   INSN_REJECTED     If instruction is one not allowed to kprobe,
>> + *   INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot.
>> + */
>> +enum probe_insn __kprobes
>> +riscv_probe_decode_insn(kprobe_opcode_t *addr, struct arch_probe_insn *api)
> 
> Please don't use __kprobes anymore. That is old stlye, instead, please
> use NOKPROBE_SYMBOL() or nokprobe_inline for static-inline function.
> (NOKPROBE_SYMBOL() will make the symbol non-inline always)

OK, should I make a note to change that in the arm64 port as well in a
separate patch?

> 
>> +{
>> +	probe_opcode_t insn = le32_to_cpu(*addr);
>> +
>> +	if (!is_compressed_insn(insn)) {
>> +		pr_warn("Can't handle non-compressed instruction %x\n", insn);
>> +		return INSN_REJECTED;
>> +	}
>> +
>> +	/* c.addisp16 imm */
>> +	if ((insn & C_ADDISP16_MASK) == C_ADDISP16_VAL) {
>> +		api->handler = simulate_caddisp16;
>> +	} else {
>> +		pr_warn("Rejected unknown instruction %x\n", insn);
>> +		return INSN_REJECTED;
>> +	}
>> +
>> +	return INSN_GOOD_NO_SLOT;
>> +}
>> diff --git a/arch/riscv/kernel/probes/decode-insn.h b/arch/riscv/kernel/probes/decode-insn.h
>> new file mode 100644
>> index 000000000000..0053ed6a308a
>> --- /dev/null
>> +++ b/arch/riscv/kernel/probes/decode-insn.h
>> @@ -0,0 +1,23 @@
>> +/* SPDX-License-Identifier: GPL-2.0+ */
>> +#ifndef _RISCV_KERNEL_KPROBES_DECODE_INSN_H
>> +#define _RISCV_KERNEL_KPROBES_DECODE_INSN_H
>> +
>> +#include <asm/sections.h>
>> +#include <asm/kprobes.h>
>> +
>> +enum probe_insn {
>> +	INSN_REJECTED,
>> +	INSN_GOOD_NO_SLOT,
>> +};
>> +
>> +/*
>> + * Compressed instruction format:
>> + * xxxxxxxxxxxxxxaa where aa != 11
>> + */
>> +#define is_compressed_insn(insn) ((insn & 0x3) != 0x3)
>> +
>> +#ifdef CONFIG_KPROBES
>> +enum probe_insn __kprobes
>> +riscv_probe_decode_insn(kprobe_opcode_t *addr, struct arch_probe_insn *asi);
>> +#endif
>> +#endif /* _RISCV_KERNEL_KPROBES_DECODE_INSN_H */
>> diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
>> new file mode 100644
>> index 000000000000..3c7b5cf72ee1
>> --- /dev/null
>> +++ b/arch/riscv/kernel/probes/kprobes.c
>> @@ -0,0 +1,401 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>> +
>> +/*
>> + * Kprobes support for RISC-V
>> + *
>> + * Author: Patrick Stählin <me@packi.ch>
>> + */
>> +#include <linux/kprobes.h>
>> +#include <linux/extable.h>
>> +#include <linux/slab.h>
>> +#include <asm/ptrace.h>
>> +#include <linux/uaccess.h>
>> +#include <asm/sections.h>
>> +
>> +#include "decode-insn.h"
>> +
>> +DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
>> +DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
>> +
>> +static void __kprobes
>> +post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
>> +
>> +static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
>> +{
>> +	if (is_compressed_insn(opcode))
>> +		*(u16 *)addr = cpu_to_le16(opcode);
>> +	else
>> +		*addr = cpu_to_le32(opcode);
>> +
>> +	return 0;
>> +}
>> +
>> +static void __kprobes arch_prepare_simulate(struct kprobe *p)
>> +{
>> +	unsigned long offset = is_compressed_insn(p->opcode) ? 2 : 4;
>> +
>> +	p->ainsn.api.restore = (unsigned long)p->addr + offset;
>> +}
>> +
>> +static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
>> +{
>> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
>> +
>> +	if (p->ainsn.api.handler)
>> +		p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);
> 
> it seems api.handler must be here, 

true

> 
>> +
>> +	/* single instruction simulated, now go for post processing */
>> +	post_kprobe_handler(kcb, regs);
>> +}
>> +
>> +int __kprobes arch_prepare_kprobe(struct kprobe *p)
>> +{
>> +	unsigned long probe_addr = (unsigned long)p->addr;
>> +	extern char __start_rodata[];
>> +	extern char __end_rodata[];
>> +
>> +	if (probe_addr & 0x1) {
>> +		pr_warn("Address not aligned.\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	/* copy instruction */
>> +	p->opcode = le32_to_cpu(*p->addr);
>> +
>> +	if (probe_addr >= (unsigned long) __start_rodata &&
>> +	    probe_addr <= (unsigned long) __end_rodata) {
>> +		return -EINVAL;
>> +	}
>> +
>> +	/* decode instruction */
>> +	switch (riscv_probe_decode_insn(p->addr, &p->ainsn.api)) {
>> +	case INSN_REJECTED:	/* insn not supported */
>> +		return -EINVAL;
>> +
>> +	case INSN_GOOD_NO_SLOT:	/* insn needs simulation */
>> +		break;
>> +	}
>> +
>> +	arch_prepare_simulate(p);
>> +
>> +	return 0;
>> +}
>> +
>> +#define C_EBREAK_OPCODE 0x9002
>> +
>> +/* arm kprobe: install breakpoint in text */
>> +void __kprobes arch_arm_kprobe(struct kprobe *p)
>> +{
>> +	patch_text(p->addr, C_EBREAK_OPCODE);
>> +}
>> +
>> +/* disarm kprobe: remove breakpoint from text */
>> +void __kprobes arch_disarm_kprobe(struct kprobe *p)
>> +{
>> +	patch_text(p->addr, p->opcode);
>> +}
>> +
>> +void __kprobes arch_remove_kprobe(struct kprobe *p)
>> +{
>> +}
>> +
>> +static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
>> +{
>> +	kcb->prev_kprobe.kp = kprobe_running();
>> +	kcb->prev_kprobe.status = kcb->kprobe_status;
>> +}
>> +
>> +static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
>> +{
>> +	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
>> +	kcb->kprobe_status = kcb->prev_kprobe.status;
>> +}
>> +
>> +static void __kprobes set_current_kprobe(struct kprobe *p)
>> +{
>> +	__this_cpu_write(current_kprobe, p);
>> +}
>> +
>> +static void __kprobes simulate(struct kprobe *p,
>> +			       struct pt_regs *regs,
>> +			       struct kprobe_ctlblk *kcb, int reenter)
>> +{
>> +	if (reenter) {
>> +		save_previous_kprobe(kcb);
>> +		set_current_kprobe(p);
>> +		kcb->kprobe_status = KPROBE_REENTER;
>> +	} else {
>> +		kcb->kprobe_status = KPROBE_HIT_SS;
>> +	}
>> +
>> +	arch_simulate_insn(p, regs);
>> +}
>> +
>> +static int __kprobes reenter_kprobe(struct kprobe *p,
>> +				    struct pt_regs *regs,
>> +				    struct kprobe_ctlblk *kcb)
>> +{
>> +	switch (kcb->kprobe_status) {
>> +	case KPROBE_HIT_SSDONE:
>> +	case KPROBE_HIT_ACTIVE:
>> +		kprobes_inc_nmissed_count(p);
>> +		simulate(p, regs, kcb, 1);
>> +		break;
>> +	case KPROBE_HIT_SS:
>> +	case KPROBE_REENTER:
>> +		pr_warn("Unrecoverable kprobe detected.\n");
>> +		dump_kprobe(p);
>> +		BUG();
>> +		break;
>> +	default:
>> +		WARN_ON(1);
>> +		return 0;
>> +	}
>> +
>> +	return 1;
> 
> If this always return 1, we can make it void return.

Agreed, I'll change that.

> 
>> +}
>> +
>> +static void __kprobes
>> +post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
>> +{
>> +	struct kprobe *cur = kprobe_running();
>> +
>> +	if (!cur)
>> +		return;
>> +
>> +	/* return addr restore if non-branching insn */
>> +	if (cur->ainsn.api.restore != 0)
>> +		instruction_pointer_set(regs, cur->ainsn.api.restore);
>> +
>> +	/* restore back original saved kprobe variables and continue */
>> +	if (kcb->kprobe_status == KPROBE_REENTER) {
>> +		restore_previous_kprobe(kcb);
>> +		return;
>> +	}
>> +	/* call post handler */
>> +	kcb->kprobe_status = KPROBE_HIT_SSDONE;
>> +	if (cur->post_handler)	{
>> +		/* post_handler can hit breakpoint and single step
>> +		 * again, so we enable D-flag for recursive exception.
>> +		 */
>> +		cur->post_handler(cur, regs, 0);
>> +	}
>> +
>> +	reset_current_kprobe();
>> +}
>> +
>> +int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int cause)
>> +{
>> +	struct kprobe *cur = kprobe_running();
>> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
>> +
>> +	switch (kcb->kprobe_status) {
>> +	case KPROBE_HIT_SS:
>> +	case KPROBE_REENTER:
>> +		/*
>> +		 * We are here because the instruction being single
>> +		 * stepped caused a page fault. We reset the current
>> +		 * kprobe and the ip points back to the probe address
>> +		 * and allow the page fault handler to continue as a
>> +		 * normal page fault.
>> +		 */
>> +		instruction_pointer_set(regs, (unsigned long) cur->addr);
>> +		if (!instruction_pointer(regs))
>> +			BUG();
> 
> Use BUG_ON().

OK

> 
>> +
>> +		if (kcb->kprobe_status == KPROBE_REENTER)
>> +			restore_previous_kprobe(kcb);
>> +		else
>> +			reset_current_kprobe();
>> +
>> +		break;
>> +	case KPROBE_HIT_ACTIVE:
>> +	case KPROBE_HIT_SSDONE:
>> +		/*
>> +		 * We increment the nmissed count for accounting,
>> +		 * we can also use npre/npostfault count for accounting
>> +		 * these specific fault cases.
>> +		 */
>> +		kprobes_inc_nmissed_count(cur);
>> +
>> +		/*
>> +		 * We come here because instructions in the pre/post
>> +		 * handler caused the page_fault, this could happen
>> +		 * if handler tries to access user space by
>> +		 * copy_from_user(), get_user() etc. Let the
>> +		 * user-specified handler try to fix it first.
>> +		 */
>> +		if (cur->fault_handler && cur->fault_handler(cur, regs, cause))
>> +			return 1;
>> +
>> +		/*
>> +		 * In case the user-specified fault handler returned
>> +		 * zero, try to fix up.
>> +		 */
>> +		if (fixup_exception(regs))
>> +			return 1;
>> +	}
>> +	return 0;
>> +}
>> +
>> +static void __kprobes kprobe_handler(struct pt_regs *regs)
>> +{
> 
> Does this handler run under local IRQ disabled? (for making sure)

Exceptions are being handled with locals IRQs _enabled_. As we've not
implemented any simulated instructions to modify the instruction
pointer, I think this is safe? Then again, I'm new to this, so please
bear with me.

> 
>> +	struct kprobe *p, *cur_kprobe;
>> +	struct kprobe_ctlblk *kcb;
>> +	unsigned long addr = instruction_pointer(regs);
>> +
>> +	kcb = get_kprobe_ctlblk();
>> +	cur_kprobe = kprobe_running();
>> +
>> +	p = get_kprobe((kprobe_opcode_t *) addr);
>> +
>> +	if (p) {
>> +		if (cur_kprobe) {
>> +			if (reenter_kprobe(p, regs, kcb))
>> +				return;
>> +		} else {
>> +			/* Probe hit */
>> +			set_current_kprobe(p);
>> +			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
>> +
>> +			/*
>> +			 * If we have no pre-handler or it returned 0, we
>> +			 * continue with normal processing.  If we have a
>> +			 * pre-handler and it returned non-zero, it will
>> +			 * modify the execution path and no need to single
>> +			 * stepping. Let's just reset current kprobe and exit.
>> +			 *
>> +			 * pre_handler can hit a breakpoint and can step thru
>> +			 * before return, keep PSTATE D-flag enabled until
>> +			 * pre_handler return back.
> 
> Is this true on RISC-V too?

It's not as we don't have a debug-unit at the moment. I'll remove the
second part of the comment block.

> 
>> +			 */
>> +			if (!p->pre_handler || !p->pre_handler(p, regs))
>> +				simulate(p, regs, kcb, 0);
>> +			else
>> +				reset_current_kprobe();
>> +		}
>> +	}
>> +	/*
>> +	 * The breakpoint instruction was removed right
>> +	 * after we hit it.  Another cpu has removed
>> +	 * either a probepoint or a debugger breakpoint
>> +	 * at this address.  In either case, no further
>> +	 * handling of this interrupt is appropriate.
>> +	 * Return back to original instruction, and continue.
>> +	 */
> 
> This should return 0 if it doesn't handle anything, but if it handles c.break
> should return 1.

I thought so too, but didn't insert one because of the comment (again,
copied from arm64). If get_kprobe doesn't return a result, it could have
been removed between the time the exception got raised or is the comment
just wrong? On the other hand, solving it this way effectively means
that we'll silently drop any other exceptions.

>> +}
>> +
>> +int __kprobes
>> +kprobe_breakpoint_handler(struct pt_regs *regs)
>> +{
>> +	kprobe_handler(regs);
>> +	return 1;
> 
> Why don't you call kprobe_handler directly?

I should.

> 
>> +}
>> +
>> +bool arch_within_kprobe_blacklist(unsigned long addr)
>> +{
>> +	if ((addr >= (unsigned long)__kprobes_text_start &&
>> +	    addr < (unsigned long)__kprobes_text_end) ||
>> +	    (addr >= (unsigned long)__entry_text_start &&
>> +	    addr < (unsigned long)__entry_text_end) ||
>> +	    !!search_exception_tables(addr))
>> +		return true;
>> +
>> +	return false;
>> +}
>> +
>> +void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
>> +{
>> +	struct kretprobe_instance *ri = NULL;
>> +	struct hlist_head *head, empty_rp;
>> +	struct hlist_node *tmp;
>> +	unsigned long flags, orig_ret_address = 0;
>> +	unsigned long trampoline_address =
>> +		(unsigned long)&kretprobe_trampoline;
>> +	kprobe_opcode_t *correct_ret_addr = NULL;
>> +
> 
> 	It seems you don't setup instruction_pointer.

I don't think I get what you mean by that. The instruction pointer (or
rather the return address register) gets set by kretprobe_trampoline.S
to the address returned from this function.

> 
>> +	INIT_HLIST_HEAD(&empty_rp);
>> +	kretprobe_hash_lock(current, &head, &flags);
>> +
>> +	/*
>> +	 * It is possible to have multiple instances associated with a given
>> +	 * task either because multiple functions in the call path have
>> +	 * return probes installed on them, and/or more than one
>> +	 * return probe was registered for a target function.
>> +	 *
>> +	 * We can handle this because:
>> +	 *     - instances are always pushed into the head of the list
>> +	 *     - when multiple return probes are registered for the same
>> +	 *	 function, the (chronologically) first instance's ret_addr
>> +	 *	 will be the real return address, and all the rest will
>> +	 *	 point to kretprobe_trampoline.
>> +	 */
>> +	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
>> +		if (ri->task != current)
>> +			/* another task is sharing our hash bucket */
>> +			continue;
>> +
>> +		orig_ret_address = (unsigned long)ri->ret_addr;
>> +
>> +		if (orig_ret_address != trampoline_address)
>> +			/*
>> +			 * This is the real return address. Any other
>> +			 * instances associated with this task are for
>> +			 * other calls deeper on the call stack
>> +			 */
>> +			break;
>> +	}
>> +
>> +	kretprobe_assert(ri, orig_ret_address, trampoline_address);
>> +
>> +	correct_ret_addr = ri->ret_addr;
>> +	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
>> +		if (ri->task != current)
>> +			/* another task is sharing our hash bucket */
>> +			continue;
>> +
>> +		orig_ret_address = (unsigned long)ri->ret_addr;
>> +		if (ri->rp && ri->rp->handler) {
>> +			__this_cpu_write(current_kprobe, &ri->rp->kp);
>> +			get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
>> +			ri->ret_addr = correct_ret_addr;
>> +			ri->rp->handler(ri, regs);
>> +			__this_cpu_write(current_kprobe, NULL);
>> +		}
>> +
>> +		recycle_rp_inst(ri, &empty_rp);
>> +
>> +		if (orig_ret_address != trampoline_address)
>> +			/*
>> +			 * This is the real return address. Any other
>> +			 * instances associated with this task are for
>> +			 * other calls deeper on the call stack
>> +			 */
>> +			break;
>> +	}
>> +
>> +	kretprobe_hash_unlock(current, &flags);
>> +
>> +	hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
>> +		hlist_del(&ri->hlist);
>> +		kfree(ri);
>> +	}
>> +	return (void *)orig_ret_address;
>> +}
>> +
>> +void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
>> +				      struct pt_regs *regs)
>> +{
>> +	ri->ret_addr = (kprobe_opcode_t *)regs->ra;
>> +	regs->ra = (long)&kretprobe_trampoline;
>> +}
>> +
>> +int __kprobes arch_trampoline_kprobe(struct kprobe *p)
>> +{
>> +	return 0;
>> +}
>> +
>> +int __init arch_init_kprobes(void)
>> +{
>> +	return 0;
>> +}
>> diff --git a/arch/riscv/kernel/probes/kprobes_trampoline.S b/arch/riscv/kernel/probes/kprobes_trampoline.S
>> new file mode 100644
>> index 000000000000..c7ceda9556a3
>> --- /dev/null
>> +++ b/arch/riscv/kernel/probes/kprobes_trampoline.S
>> @@ -0,0 +1,91 @@
>> +/* SPDX-License-Identifier: GPL-2.0+ */
>> +
>> +#include <linux/linkage.h>
>> +
>> +#include <asm/asm.h>
>> +#include <asm/asm-offsets.h>
>> +
>> +	.text
>> +	.altmacro
>> +
>> +	.macro save_all_base_regs
>> +	REG_S x1,  PT_RA(sp)
>> +	REG_S x3,  PT_GP(sp)
>> +	REG_S x4,  PT_TP(sp)
>> +	REG_S x5,  PT_T0(sp)
>> +	REG_S x6,  PT_T1(sp)
>> +	REG_S x7,  PT_T2(sp)
>> +	REG_S x8,  PT_S0(sp)
>> +	REG_S x9,  PT_S1(sp)
>> +	REG_S x10, PT_A0(sp)
>> +	REG_S x11, PT_A1(sp)
>> +	REG_S x12, PT_A2(sp)
>> +	REG_S x13, PT_A3(sp)
>> +	REG_S x14, PT_A4(sp)
>> +	REG_S x15, PT_A5(sp)
>> +	REG_S x16, PT_A6(sp)
>> +	REG_S x17, PT_A7(sp)
>> +	REG_S x18, PT_S2(sp)
>> +	REG_S x19, PT_S3(sp)
>> +	REG_S x20, PT_S4(sp)
>> +	REG_S x21, PT_S5(sp)
>> +	REG_S x22, PT_S6(sp)
>> +	REG_S x23, PT_S7(sp)
>> +	REG_S x24, PT_S8(sp)
>> +	REG_S x25, PT_S9(sp)
>> +	REG_S x26, PT_S10(sp)
>> +	REG_S x27, PT_S11(sp)
>> +	REG_S x28, PT_T3(sp)
>> +	REG_S x29, PT_T4(sp)
>> +	REG_S x30, PT_T5(sp)
>> +	REG_S x31, PT_T6(sp)
>> +	.endm
>> +
>> +	.macro restore_all_base_regs
>> +	REG_L x3,  PT_GP(sp)
>> +	REG_L x4,  PT_TP(sp)
>> +	REG_L x5,  PT_T0(sp)
>> +	REG_L x6,  PT_T1(sp)
>> +	REG_L x7,  PT_T2(sp)
>> +	REG_L x8,  PT_S0(sp)
>> +	REG_L x9,  PT_S1(sp)
>> +	REG_L x10, PT_A0(sp)
>> +	REG_L x11, PT_A1(sp)
>> +	REG_L x12, PT_A2(sp)
>> +	REG_L x13, PT_A3(sp)
>> +	REG_L x14, PT_A4(sp)
>> +	REG_L x15, PT_A5(sp)
>> +	REG_L x16, PT_A6(sp)
>> +	REG_L x17, PT_A7(sp)
>> +	REG_L x18, PT_S2(sp)
>> +	REG_L x19, PT_S3(sp)
>> +	REG_L x20, PT_S4(sp)
>> +	REG_L x21, PT_S5(sp)
>> +	REG_L x22, PT_S6(sp)
>> +	REG_L x23, PT_S7(sp)
>> +	REG_L x24, PT_S8(sp)
>> +	REG_L x25, PT_S9(sp)
>> +	REG_L x26, PT_S10(sp)
>> +	REG_L x27, PT_S11(sp)
>> +	REG_L x28, PT_T3(sp)
>> +	REG_L x29, PT_T4(sp)
>> +	REG_L x30, PT_T5(sp)
>> +	REG_L x31, PT_T6(sp)
>> +	.endm
>> +
>> +ENTRY(kretprobe_trampoline)
>> +	addi sp, sp, -(PT_SIZE_ON_STACK)
>> +	save_all_base_regs
>> +
>> +	move a0, sp /* pt_regs */
>> +
>> +	call trampoline_probe_handler
>> +
>> +	/* use the result as the return-address */
>> +	move ra, a0
>> +
>> +	restore_all_base_regs
>> +	addi sp, sp, PT_SIZE_ON_STACK
>> +
>> +	ret
>> +ENDPROC(kretprobe_trampoline)
>> diff --git a/arch/riscv/kernel/probes/simulate-insn.c b/arch/riscv/kernel/probes/simulate-insn.c
>> new file mode 100644
>> index 000000000000..5734d9bae22f
>> --- /dev/null
>> +++ b/arch/riscv/kernel/probes/simulate-insn.c
>> @@ -0,0 +1,33 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>> +
>> +#include <linux/bitops.h>
>> +#include <linux/kernel.h>
>> +#include <linux/kprobes.h>
>> +
>> +#include "simulate-insn.h"
>> +
>> +#define bit_at(value, bit)		((value) & (1 << (bit)))
>> +#define move_bit_at(value, bit, to)	((bit_at(value, bit) >> bit) << to)
>> +
>> +void __kprobes
>> +simulate_caddisp16(u32 opcode, long addr, struct pt_regs *regs)
>> +{
>> +	s16 imm;
>> +
>> +	/*
>> +	 * Immediate value layout in c.addisp16:
>> +	 * xxx9 xxxx x468 75xx
>> +	 * 1  1    8    4    0
>> +	 * 5  2
>> +	 */
>> +	imm = sign_extend32(
>> +		move_bit_at(opcode, 12, 9) |
>> +		move_bit_at(opcode, 6, 4) |
>> +		move_bit_at(opcode, 5, 6) |
>> +		move_bit_at(opcode, 4, 8) |
>> +		move_bit_at(opcode, 3, 7) |
>> +		move_bit_at(opcode, 2, 5),
>> +		9);
>> +
>> +	regs->sp += imm;
> 
> What about updating regs->sepc?

sepc gets updated by instruction_pointer_set in kprobe_handler

> 
>> +}
>> diff --git a/arch/riscv/kernel/probes/simulate-insn.h b/arch/riscv/kernel/probes/simulate-insn.h
>> new file mode 100644
>> index 000000000000..dc2c06c30167
>> --- /dev/null
>> +++ b/arch/riscv/kernel/probes/simulate-insn.h
>> @@ -0,0 +1,8 @@
>> +/* SPDX-License-Identifier: GPL-2.0+ */
>> +
>> +#ifndef _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H
>> +#define _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H
>> +
>> +void simulate_caddisp16(u32 opcode, long addr, struct pt_regs *regs);
>> +
>> +#endif /* _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H */
>> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
>> index 24a9333dda2c..d7113178d401 100644
>> --- a/arch/riscv/kernel/traps.c
>> +++ b/arch/riscv/kernel/traps.c
>> @@ -18,6 +18,7 @@
>>  #include <linux/sched/signal.h>
>>  #include <linux/signal.h>
>>  #include <linux/kdebug.h>
>> +#include <linux/kprobes.h>
>>  #include <linux/uaccess.h>
>>  #include <linux/mm.h>
>>  #include <linux/module.h>
>> @@ -120,8 +121,14 @@ DO_ERROR_INFO(do_trap_ecall_m,
>>  
>>  asmlinkage void do_trap_break(struct pt_regs *regs)
>>  {
>> +	bool handler_found = false;
>> +
>> +#ifdef CONFIG_KPROBES
>> +	if (kprobe_breakpoint_handler(regs))
>> +		handler_found = 1;
> 
> Why don't you just return from here?

Following the pattern I've seen in other places, I can change that.

> 
>> +#endif
>>  #ifdef CONFIG_GENERIC_BUG
>> -	if (!user_mode(regs)) {
>> +	if (!handler_found && !user_mode(regs)) {
>>  		enum bug_trap_type type;
>>  
>>  		type = report_bug(regs->sepc, regs);
>> @@ -137,7 +144,9 @@ asmlinkage void do_trap_break(struct pt_regs *regs)
>>  	}
>>  #endif /* CONFIG_GENERIC_BUG */
>>  
>> -	force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)(regs->sepc), current);
>> +	if (!handler_found)
>> +		force_sig_fault(SIGTRAP, TRAP_BRKPT,
>> +			(void __user *)(regs->sepc), current);
>>  }
>>  
>>  #ifdef CONFIG_GENERIC_BUG
>> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
>> index 88401d5125bc..eff816e33479 100644
>> --- a/arch/riscv/mm/fault.c
>> +++ b/arch/riscv/mm/fault.c
>> @@ -22,6 +22,7 @@
>>  
>>  #include <linux/mm.h>
>>  #include <linux/kernel.h>
>> +#include <linux/kprobes.h>
>>  #include <linux/interrupt.h>
>>  #include <linux/perf_event.h>
>>  #include <linux/signal.h>
>> @@ -30,11 +31,33 @@
>>  #include <asm/pgalloc.h>
>>  #include <asm/ptrace.h>
>>  
>> +#ifdef CONFIG_KPROBES
>> +static inline int notify_page_fault(struct pt_regs *regs, unsigned int cause)
> 
> please use nokprobe_inline.

OK.

> 
>> +{
>> +	int ret = 0;
>> +
>> +	/* kprobe_running() needs smp_processor_id() */
>> +	if (!user_mode(regs)) {
>> +		preempt_disable();
>> +		if (kprobe_running() && kprobe_fault_handler(regs, cause))
>> +			ret = 1;
>> +		preempt_enable();
>> +	}
>> +
>> +	return ret;
>> +}
>> +#else
>> +static inline int notify_page_fault(struct pt_regs *regs, unsigned int cause)
>> +{
>> +	return 0;
>> +}
>> +#endif
>> +
>>  /*
>>   * This routine handles page faults.  It determines the address and the
>>   * problem, and then passes it off to one of the appropriate routines.
>>   */
>> -asmlinkage void do_page_fault(struct pt_regs *regs)
>> +asmlinkage void __kprobes do_page_fault(struct pt_regs *regs)
>>  {
>>  	struct task_struct *tsk;
>>  	struct vm_area_struct *vma;
>> @@ -47,6 +70,9 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
>>  	cause = regs->scause;
>>  	addr = regs->sbadaddr;
>>  
>> +	if (notify_page_fault(regs, cause))
>> +		return;
>> +
>>  	tsk = current;
>>  	mm = tsk->mm;
>>  
>> -- 
>> 2.17.1
>>
> 
> Thank you,
> 

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

^ permalink raw reply	[flat|nested] 18+ messages in thread

* [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support
  2018-11-14 15:49     ` mhiramat
  2018-11-14 15:49       ` Masami Hiramatsu
@ 2018-11-14 21:10       ` me
  2018-11-14 21:10         ` Patrick Staehlin
  2018-11-15  7:50         ` mhiramat
  1 sibling, 2 replies; 18+ messages in thread
From: me @ 2018-11-14 21:10 UTC (permalink / raw)
  To: linux-riscv

On 14.11.18 16:49, Masami Hiramatsu wrote:
> On Wed, 14 Nov 2018 00:37:30 -0800
> Masami Hiramatsu <mhiramat@kernel.org> wrote:
> 
>>> +
>>> +static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
>>> +{
>>> +	if (is_compressed_insn(opcode))
>>> +		*(u16 *)addr = cpu_to_le16(opcode);
>>> +	else
>>> +		*addr = cpu_to_le32(opcode);
>>> +
> 
> BTW, don't RISC-V need any i-cache flush and per-core serialization
> for patching the text area? (and no text_mutex protection?)

Yes, we should probably call flush_icache_all. This code works on
QEMU/virt but I guess on real hardware you may run into problems,
especially when disarming the kprobe. I'll have a look at the arm64 code
again to see what's missing.

> 
>>> diff --git a/arch/riscv/kernel/probes/kprobes_trampoline.S b/arch/riscv/kernel/probes/kprobes_trampoline.S
>>> new file mode 100644
>>> index 000000000000..c7ceda9556a3
>>> --- /dev/null
>>> +++ b/arch/riscv/kernel/probes/kprobes_trampoline.S
>>> @@ -0,0 +1,91 @@
>>> +/* SPDX-License-Identifier: GPL-2.0+ */
>>> +
>>> +#include <linux/linkage.h>
>>> +
>>> +#include <asm/asm.h>
>>> +#include <asm/asm-offsets.h>
>>> +
>>> +	.text
>>> +	.altmacro
>>> +
>>> +	.macro save_all_base_regs
>>> +	REG_S x1,  PT_RA(sp)
>>> +	REG_S x3,  PT_GP(sp)
>>> +	REG_S x4,  PT_TP(sp)
>>> +	REG_S x5,  PT_T0(sp)
>>> +	REG_S x6,  PT_T1(sp)
>>> +	REG_S x7,  PT_T2(sp)
>>> +	REG_S x8,  PT_S0(sp)
>>> +	REG_S x9,  PT_S1(sp)
>>> +	REG_S x10, PT_A0(sp)
>>> +	REG_S x11, PT_A1(sp)
>>> +	REG_S x12, PT_A2(sp)
>>> +	REG_S x13, PT_A3(sp)
>>> +	REG_S x14, PT_A4(sp)
>>> +	REG_S x15, PT_A5(sp)
>>> +	REG_S x16, PT_A6(sp)
>>> +	REG_S x17, PT_A7(sp)
>>> +	REG_S x18, PT_S2(sp)
>>> +	REG_S x19, PT_S3(sp)
>>> +	REG_S x20, PT_S4(sp)
>>> +	REG_S x21, PT_S5(sp)
>>> +	REG_S x22, PT_S6(sp)
>>> +	REG_S x23, PT_S7(sp)
>>> +	REG_S x24, PT_S8(sp)
>>> +	REG_S x25, PT_S9(sp)
>>> +	REG_S x26, PT_S10(sp)
>>> +	REG_S x27, PT_S11(sp)
>>> +	REG_S x28, PT_T3(sp)
>>> +	REG_S x29, PT_T4(sp)
>>> +	REG_S x30, PT_T5(sp)
>>> +	REG_S x31, PT_T6(sp)
>>> +	.endm
>>> +
>>> +	.macro restore_all_base_regs
>>> +	REG_L x3,  PT_GP(sp)
>>> +	REG_L x4,  PT_TP(sp)
>>> +	REG_L x5,  PT_T0(sp)
>>> +	REG_L x6,  PT_T1(sp)
>>> +	REG_L x7,  PT_T2(sp)
>>> +	REG_L x8,  PT_S0(sp)
>>> +	REG_L x9,  PT_S1(sp)
>>> +	REG_L x10, PT_A0(sp)
>>> +	REG_L x11, PT_A1(sp)
>>> +	REG_L x12, PT_A2(sp)
>>> +	REG_L x13, PT_A3(sp)
>>> +	REG_L x14, PT_A4(sp)
>>> +	REG_L x15, PT_A5(sp)
>>> +	REG_L x16, PT_A6(sp)
>>> +	REG_L x17, PT_A7(sp)
>>> +	REG_L x18, PT_S2(sp)
>>> +	REG_L x19, PT_S3(sp)
>>> +	REG_L x20, PT_S4(sp)
>>> +	REG_L x21, PT_S5(sp)
>>> +	REG_L x22, PT_S6(sp)
>>> +	REG_L x23, PT_S7(sp)
>>> +	REG_L x24, PT_S8(sp)
>>> +	REG_L x25, PT_S9(sp)
>>> +	REG_L x26, PT_S10(sp)
>>> +	REG_L x27, PT_S11(sp)
>>> +	REG_L x28, PT_T3(sp)
>>> +	REG_L x29, PT_T4(sp)
>>> +	REG_L x30, PT_T5(sp)
>>> +	REG_L x31, PT_T6(sp)
>>> +	.endm
> 
> 
> It seems thses macros can be (partially?) shared with entry.S

Yes, I wanted to avoid somebody changing the shared code and breaking
random things. But that's what reviews are for. I'll think of something
for v2.

^ permalink raw reply	[flat|nested] 18+ messages in thread

* Re: [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support
  2018-11-14 21:10       ` me
@ 2018-11-14 21:10         ` Patrick Staehlin
  2018-11-15  7:50         ` mhiramat
  1 sibling, 0 replies; 18+ messages in thread
From: Patrick Staehlin @ 2018-11-14 21:10 UTC (permalink / raw)
  To: Masami Hiramatsu
  Cc: Albert Ou, Anders Roxell, Andrew Morton, Alan Kao,
	Catalin Marinas, Palmer Dabbelt, Will Deacon, linux-kernel,
	Al Viro, Souptick Joarder, Zong Li, Thomas Gleixner,
	Eric W. Biederman, linux-riscv, zhong jiang, Ingo Molnar,
	Luc Van Oostenryck, Jim Wilson

On 14.11.18 16:49, Masami Hiramatsu wrote:
> On Wed, 14 Nov 2018 00:37:30 -0800
> Masami Hiramatsu <mhiramat@kernel.org> wrote:
> 
>>> +
>>> +static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
>>> +{
>>> +	if (is_compressed_insn(opcode))
>>> +		*(u16 *)addr = cpu_to_le16(opcode);
>>> +	else
>>> +		*addr = cpu_to_le32(opcode);
>>> +
> 
> BTW, don't RISC-V need any i-cache flush and per-core serialization
> for patching the text area? (and no text_mutex protection?)

Yes, we should probably call flush_icache_all. This code works on
QEMU/virt but I guess on real hardware you may run into problems,
especially when disarming the kprobe. I'll have a look at the arm64 code
again to see what's missing.

> 
>>> diff --git a/arch/riscv/kernel/probes/kprobes_trampoline.S b/arch/riscv/kernel/probes/kprobes_trampoline.S
>>> new file mode 100644
>>> index 000000000000..c7ceda9556a3
>>> --- /dev/null
>>> +++ b/arch/riscv/kernel/probes/kprobes_trampoline.S
>>> @@ -0,0 +1,91 @@
>>> +/* SPDX-License-Identifier: GPL-2.0+ */
>>> +
>>> +#include <linux/linkage.h>
>>> +
>>> +#include <asm/asm.h>
>>> +#include <asm/asm-offsets.h>
>>> +
>>> +	.text
>>> +	.altmacro
>>> +
>>> +	.macro save_all_base_regs
>>> +	REG_S x1,  PT_RA(sp)
>>> +	REG_S x3,  PT_GP(sp)
>>> +	REG_S x4,  PT_TP(sp)
>>> +	REG_S x5,  PT_T0(sp)
>>> +	REG_S x6,  PT_T1(sp)
>>> +	REG_S x7,  PT_T2(sp)
>>> +	REG_S x8,  PT_S0(sp)
>>> +	REG_S x9,  PT_S1(sp)
>>> +	REG_S x10, PT_A0(sp)
>>> +	REG_S x11, PT_A1(sp)
>>> +	REG_S x12, PT_A2(sp)
>>> +	REG_S x13, PT_A3(sp)
>>> +	REG_S x14, PT_A4(sp)
>>> +	REG_S x15, PT_A5(sp)
>>> +	REG_S x16, PT_A6(sp)
>>> +	REG_S x17, PT_A7(sp)
>>> +	REG_S x18, PT_S2(sp)
>>> +	REG_S x19, PT_S3(sp)
>>> +	REG_S x20, PT_S4(sp)
>>> +	REG_S x21, PT_S5(sp)
>>> +	REG_S x22, PT_S6(sp)
>>> +	REG_S x23, PT_S7(sp)
>>> +	REG_S x24, PT_S8(sp)
>>> +	REG_S x25, PT_S9(sp)
>>> +	REG_S x26, PT_S10(sp)
>>> +	REG_S x27, PT_S11(sp)
>>> +	REG_S x28, PT_T3(sp)
>>> +	REG_S x29, PT_T4(sp)
>>> +	REG_S x30, PT_T5(sp)
>>> +	REG_S x31, PT_T6(sp)
>>> +	.endm
>>> +
>>> +	.macro restore_all_base_regs
>>> +	REG_L x3,  PT_GP(sp)
>>> +	REG_L x4,  PT_TP(sp)
>>> +	REG_L x5,  PT_T0(sp)
>>> +	REG_L x6,  PT_T1(sp)
>>> +	REG_L x7,  PT_T2(sp)
>>> +	REG_L x8,  PT_S0(sp)
>>> +	REG_L x9,  PT_S1(sp)
>>> +	REG_L x10, PT_A0(sp)
>>> +	REG_L x11, PT_A1(sp)
>>> +	REG_L x12, PT_A2(sp)
>>> +	REG_L x13, PT_A3(sp)
>>> +	REG_L x14, PT_A4(sp)
>>> +	REG_L x15, PT_A5(sp)
>>> +	REG_L x16, PT_A6(sp)
>>> +	REG_L x17, PT_A7(sp)
>>> +	REG_L x18, PT_S2(sp)
>>> +	REG_L x19, PT_S3(sp)
>>> +	REG_L x20, PT_S4(sp)
>>> +	REG_L x21, PT_S5(sp)
>>> +	REG_L x22, PT_S6(sp)
>>> +	REG_L x23, PT_S7(sp)
>>> +	REG_L x24, PT_S8(sp)
>>> +	REG_L x25, PT_S9(sp)
>>> +	REG_L x26, PT_S10(sp)
>>> +	REG_L x27, PT_S11(sp)
>>> +	REG_L x28, PT_T3(sp)
>>> +	REG_L x29, PT_T4(sp)
>>> +	REG_L x30, PT_T5(sp)
>>> +	REG_L x31, PT_T6(sp)
>>> +	.endm
> 
> 
> It seems thses macros can be (partially?) shared with entry.S

Yes, I wanted to avoid somebody changing the shared code and breaking
random things. But that's what reviews are for. I'll think of something
for v2.

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

^ permalink raw reply	[flat|nested] 18+ messages in thread

* [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support
  2018-11-14 21:10       ` me
  2018-11-14 21:10         ` Patrick Staehlin
@ 2018-11-15  7:50         ` mhiramat
  2018-11-15  7:50           ` Masami Hiramatsu
  1 sibling, 1 reply; 18+ messages in thread
From: mhiramat @ 2018-11-15  7:50 UTC (permalink / raw)
  To: linux-riscv

On Wed, 14 Nov 2018 22:10:52 +0100
Patrick Staehlin <me@packi.ch> wrote:

> On 14.11.18 16:49, Masami Hiramatsu wrote:
> > On Wed, 14 Nov 2018 00:37:30 -0800
> > Masami Hiramatsu <mhiramat@kernel.org> wrote:
> > 
> >>> +
> >>> +static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
> >>> +{
> >>> +	if (is_compressed_insn(opcode))
> >>> +		*(u16 *)addr = cpu_to_le16(opcode);
> >>> +	else
> >>> +		*addr = cpu_to_le32(opcode);
> >>> +
> > 
> > BTW, don't RISC-V need any i-cache flush and per-core serialization
> > for patching the text area? (and no text_mutex protection?)
> 
> Yes, we should probably call flush_icache_all. This code works on
> QEMU/virt but I guess on real hardware you may run into problems,
> especially when disarming the kprobe. I'll have a look at the arm64 code
> again to see what's missing.

Note that self code-modifying is a special case for any processors, especially
if that is multi-processor. In general, this may depend on the circuit desgin,
not ISA.
Some processor implementation will do in-order and no i-cache, no SMP, that will
be simple, but if it is out-of-order, deep pipeline, huge i-cache, and many-core,
you might have to care many things. We have to talk with someone who is designing
real hardware, and maybe better to make the patch_text pluggable for variants.
(or choose the safest way)

> >>> diff --git a/arch/riscv/kernel/probes/kprobes_trampoline.S b/arch/riscv/kernel/probes/kprobes_trampoline.S
> >>> new file mode 100644
> >>> index 000000000000..c7ceda9556a3
> >>> --- /dev/null
> >>> +++ b/arch/riscv/kernel/probes/kprobes_trampoline.S
> >>> @@ -0,0 +1,91 @@
> >>> +/* SPDX-License-Identifier: GPL-2.0+ */
> >>> +
> >>> +#include <linux/linkage.h>
> >>> +
> >>> +#include <asm/asm.h>
> >>> +#include <asm/asm-offsets.h>
> >>> +
> >>> +	.text
> >>> +	.altmacro
> >>> +
> >>> +	.macro save_all_base_regs
> >>> +	REG_S x1,  PT_RA(sp)
> >>> +	REG_S x3,  PT_GP(sp)
> >>> +	REG_S x4,  PT_TP(sp)
> >>> +	REG_S x5,  PT_T0(sp)
> >>> +	REG_S x6,  PT_T1(sp)
> >>> +	REG_S x7,  PT_T2(sp)
> >>> +	REG_S x8,  PT_S0(sp)
> >>> +	REG_S x9,  PT_S1(sp)
> >>> +	REG_S x10, PT_A0(sp)
> >>> +	REG_S x11, PT_A1(sp)
> >>> +	REG_S x12, PT_A2(sp)
> >>> +	REG_S x13, PT_A3(sp)
> >>> +	REG_S x14, PT_A4(sp)
> >>> +	REG_S x15, PT_A5(sp)
> >>> +	REG_S x16, PT_A6(sp)
> >>> +	REG_S x17, PT_A7(sp)
> >>> +	REG_S x18, PT_S2(sp)
> >>> +	REG_S x19, PT_S3(sp)
> >>> +	REG_S x20, PT_S4(sp)
> >>> +	REG_S x21, PT_S5(sp)
> >>> +	REG_S x22, PT_S6(sp)
> >>> +	REG_S x23, PT_S7(sp)
> >>> +	REG_S x24, PT_S8(sp)
> >>> +	REG_S x25, PT_S9(sp)
> >>> +	REG_S x26, PT_S10(sp)
> >>> +	REG_S x27, PT_S11(sp)
> >>> +	REG_S x28, PT_T3(sp)
> >>> +	REG_S x29, PT_T4(sp)
> >>> +	REG_S x30, PT_T5(sp)
> >>> +	REG_S x31, PT_T6(sp)
> >>> +	.endm
> >>> +
> >>> +	.macro restore_all_base_regs
> >>> +	REG_L x3,  PT_GP(sp)
> >>> +	REG_L x4,  PT_TP(sp)
> >>> +	REG_L x5,  PT_T0(sp)
> >>> +	REG_L x6,  PT_T1(sp)
> >>> +	REG_L x7,  PT_T2(sp)
> >>> +	REG_L x8,  PT_S0(sp)
> >>> +	REG_L x9,  PT_S1(sp)
> >>> +	REG_L x10, PT_A0(sp)
> >>> +	REG_L x11, PT_A1(sp)
> >>> +	REG_L x12, PT_A2(sp)
> >>> +	REG_L x13, PT_A3(sp)
> >>> +	REG_L x14, PT_A4(sp)
> >>> +	REG_L x15, PT_A5(sp)
> >>> +	REG_L x16, PT_A6(sp)
> >>> +	REG_L x17, PT_A7(sp)
> >>> +	REG_L x18, PT_S2(sp)
> >>> +	REG_L x19, PT_S3(sp)
> >>> +	REG_L x20, PT_S4(sp)
> >>> +	REG_L x21, PT_S5(sp)
> >>> +	REG_L x22, PT_S6(sp)
> >>> +	REG_L x23, PT_S7(sp)
> >>> +	REG_L x24, PT_S8(sp)
> >>> +	REG_L x25, PT_S9(sp)
> >>> +	REG_L x26, PT_S10(sp)
> >>> +	REG_L x27, PT_S11(sp)
> >>> +	REG_L x28, PT_T3(sp)
> >>> +	REG_L x29, PT_T4(sp)
> >>> +	REG_L x30, PT_T5(sp)
> >>> +	REG_L x31, PT_T6(sp)
> >>> +	.endm
> > 
> > 
> > It seems thses macros can be (partially?) shared with entry.S
> 
> Yes, I wanted to avoid somebody changing the shared code and breaking
> random things. But that's what reviews are for. I'll think of something
> for v2.

Ah, OK. So for the first version, we introduce this separated code until
someone complains it.


Thank you,

-- 
Masami Hiramatsu <mhiramat@kernel.org>

^ permalink raw reply	[flat|nested] 18+ messages in thread

* Re: [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support
  2018-11-15  7:50         ` mhiramat
@ 2018-11-15  7:50           ` Masami Hiramatsu
  0 siblings, 0 replies; 18+ messages in thread
From: Masami Hiramatsu @ 2018-11-15  7:50 UTC (permalink / raw)
  To: Patrick Staehlin
  Cc: Albert Ou, Anders Roxell, Andrew Morton, Alan Kao,
	Catalin Marinas, Palmer Dabbelt, Will Deacon, linux-kernel,
	Al Viro, Souptick Joarder, Zong Li, Thomas Gleixner,
	Eric W. Biederman, linux-riscv, zhong jiang, Ingo Molnar,
	Luc Van Oostenryck, Jim Wilson

On Wed, 14 Nov 2018 22:10:52 +0100
Patrick Staehlin <me@packi.ch> wrote:

> On 14.11.18 16:49, Masami Hiramatsu wrote:
> > On Wed, 14 Nov 2018 00:37:30 -0800
> > Masami Hiramatsu <mhiramat@kernel.org> wrote:
> > 
> >>> +
> >>> +static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
> >>> +{
> >>> +	if (is_compressed_insn(opcode))
> >>> +		*(u16 *)addr = cpu_to_le16(opcode);
> >>> +	else
> >>> +		*addr = cpu_to_le32(opcode);
> >>> +
> > 
> > BTW, don't RISC-V need any i-cache flush and per-core serialization
> > for patching the text area? (and no text_mutex protection?)
> 
> Yes, we should probably call flush_icache_all. This code works on
> QEMU/virt but I guess on real hardware you may run into problems,
> especially when disarming the kprobe. I'll have a look at the arm64 code
> again to see what's missing.

Note that self code-modifying is a special case for any processors, especially
if that is multi-processor. In general, this may depend on the circuit desgin,
not ISA.
Some processor implementation will do in-order and no i-cache, no SMP, that will
be simple, but if it is out-of-order, deep pipeline, huge i-cache, and many-core,
you might have to care many things. We have to talk with someone who is designing
real hardware, and maybe better to make the patch_text pluggable for variants.
(or choose the safest way)

> >>> diff --git a/arch/riscv/kernel/probes/kprobes_trampoline.S b/arch/riscv/kernel/probes/kprobes_trampoline.S
> >>> new file mode 100644
> >>> index 000000000000..c7ceda9556a3
> >>> --- /dev/null
> >>> +++ b/arch/riscv/kernel/probes/kprobes_trampoline.S
> >>> @@ -0,0 +1,91 @@
> >>> +/* SPDX-License-Identifier: GPL-2.0+ */
> >>> +
> >>> +#include <linux/linkage.h>
> >>> +
> >>> +#include <asm/asm.h>
> >>> +#include <asm/asm-offsets.h>
> >>> +
> >>> +	.text
> >>> +	.altmacro
> >>> +
> >>> +	.macro save_all_base_regs
> >>> +	REG_S x1,  PT_RA(sp)
> >>> +	REG_S x3,  PT_GP(sp)
> >>> +	REG_S x4,  PT_TP(sp)
> >>> +	REG_S x5,  PT_T0(sp)
> >>> +	REG_S x6,  PT_T1(sp)
> >>> +	REG_S x7,  PT_T2(sp)
> >>> +	REG_S x8,  PT_S0(sp)
> >>> +	REG_S x9,  PT_S1(sp)
> >>> +	REG_S x10, PT_A0(sp)
> >>> +	REG_S x11, PT_A1(sp)
> >>> +	REG_S x12, PT_A2(sp)
> >>> +	REG_S x13, PT_A3(sp)
> >>> +	REG_S x14, PT_A4(sp)
> >>> +	REG_S x15, PT_A5(sp)
> >>> +	REG_S x16, PT_A6(sp)
> >>> +	REG_S x17, PT_A7(sp)
> >>> +	REG_S x18, PT_S2(sp)
> >>> +	REG_S x19, PT_S3(sp)
> >>> +	REG_S x20, PT_S4(sp)
> >>> +	REG_S x21, PT_S5(sp)
> >>> +	REG_S x22, PT_S6(sp)
> >>> +	REG_S x23, PT_S7(sp)
> >>> +	REG_S x24, PT_S8(sp)
> >>> +	REG_S x25, PT_S9(sp)
> >>> +	REG_S x26, PT_S10(sp)
> >>> +	REG_S x27, PT_S11(sp)
> >>> +	REG_S x28, PT_T3(sp)
> >>> +	REG_S x29, PT_T4(sp)
> >>> +	REG_S x30, PT_T5(sp)
> >>> +	REG_S x31, PT_T6(sp)
> >>> +	.endm
> >>> +
> >>> +	.macro restore_all_base_regs
> >>> +	REG_L x3,  PT_GP(sp)
> >>> +	REG_L x4,  PT_TP(sp)
> >>> +	REG_L x5,  PT_T0(sp)
> >>> +	REG_L x6,  PT_T1(sp)
> >>> +	REG_L x7,  PT_T2(sp)
> >>> +	REG_L x8,  PT_S0(sp)
> >>> +	REG_L x9,  PT_S1(sp)
> >>> +	REG_L x10, PT_A0(sp)
> >>> +	REG_L x11, PT_A1(sp)
> >>> +	REG_L x12, PT_A2(sp)
> >>> +	REG_L x13, PT_A3(sp)
> >>> +	REG_L x14, PT_A4(sp)
> >>> +	REG_L x15, PT_A5(sp)
> >>> +	REG_L x16, PT_A6(sp)
> >>> +	REG_L x17, PT_A7(sp)
> >>> +	REG_L x18, PT_S2(sp)
> >>> +	REG_L x19, PT_S3(sp)
> >>> +	REG_L x20, PT_S4(sp)
> >>> +	REG_L x21, PT_S5(sp)
> >>> +	REG_L x22, PT_S6(sp)
> >>> +	REG_L x23, PT_S7(sp)
> >>> +	REG_L x24, PT_S8(sp)
> >>> +	REG_L x25, PT_S9(sp)
> >>> +	REG_L x26, PT_S10(sp)
> >>> +	REG_L x27, PT_S11(sp)
> >>> +	REG_L x28, PT_T3(sp)
> >>> +	REG_L x29, PT_T4(sp)
> >>> +	REG_L x30, PT_T5(sp)
> >>> +	REG_L x31, PT_T6(sp)
> >>> +	.endm
> > 
> > 
> > It seems thses macros can be (partially?) shared with entry.S
> 
> Yes, I wanted to avoid somebody changing the shared code and breaking
> random things. But that's what reviews are for. I'll think of something
> for v2.

Ah, OK. So for the first version, we introduce this separated code until
someone complains it.


Thank you,

-- 
Masami Hiramatsu <mhiramat@kernel.org>

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

^ permalink raw reply	[flat|nested] 18+ messages in thread

* [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support
  2018-11-14 20:52     ` me
  2018-11-14 20:52       ` Patrick Staehlin
@ 2018-11-15  8:41       ` mhiramat
  2018-11-15  8:41         ` Masami Hiramatsu
  1 sibling, 1 reply; 18+ messages in thread
From: mhiramat @ 2018-11-15  8:41 UTC (permalink / raw)
  To: linux-riscv

On Wed, 14 Nov 2018 21:52:57 +0100
Patrick Staehlin <me@packi.ch> wrote:

> Hi Masami,
> 
> thank you for your remarks.
> 
> On 14.11.18 09:37, Masami Hiramatsu wrote>
> > Thank you very much for implementing kprobes on RISC-V :)
> > 
> > On Tue, 13 Nov 2018 20:58:04 +0100
> > Patrick St?hlin <me@packi.ch> wrote:
> > 
> >> First implementation, adapted from arm64. The C.ADDISP16 instruction
> >> gets simulated and the kprobes-handler called by inserting a C.EBREAK
> >> instruction.
> >>
> >> C.ADDISP16 was chosen as it sets-up the stack frame for functions.
> >> Some work has been done to support probes on non-compressed
> >> instructions but there is no support yet for decoding those.
> > 
> > Does this only support C.ADDISP16? No other insns are supported?
> > Supporting 1 insn is too few I think.
> 
> At the moment, yes. I'm waiting for some input from somebody with deeper
> insights into the RISC-V architecture than me before implementing more
> instructions, should solution I've chosen be woefully inadequate.

I think starting with a few emulatable set of instruction support is good
to me. But maybe we need more... 1 instruction is too limited.


> > Can RISC-V do single stepping? If not, we need to prepare emulator
> > as match as possible, or for ALU instructions, we can run it on
> > buffer and hook it.
> 
> The debug-specification is still a draft but there are some softcores
> that implement it. But even if it was finalized I don't think this will
> be made a mandatory extension so we need to simulate/emulate a good part
> of the instruction set anyway.

OK.

[...]
> >> diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c
> >> new file mode 100644
> >> index 000000000000..2d8f46f4c2e7
> >> --- /dev/null
> >> +++ b/arch/riscv/kernel/probes/decode-insn.c
> >> @@ -0,0 +1,38 @@
> >> +// SPDX-License-Identifier: GPL-2.0+
> >> +
> >> +#include <linux/kernel.h>
> >> +#include <linux/kprobes.h>
> >> +#include <linux/module.h>
> >> +#include <linux/kallsyms.h>
> >> +#include <asm/sections.h>
> >> +
> >> +#include "decode-insn.h"
> >> +#include "simulate-insn.h"
> >> +
> >> +#define C_ADDISP16_MASK 0x6F83
> >> +#define C_ADDISP16_VAL  0x6101
> >> +
> >> +/* Return:
> >> + *   INSN_REJECTED     If instruction is one not allowed to kprobe,
> >> + *   INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot.
> >> + */
> >> +enum probe_insn __kprobes
> >> +riscv_probe_decode_insn(kprobe_opcode_t *addr, struct arch_probe_insn *api)
> > 
> > Please don't use __kprobes anymore. That is old stlye, instead, please
> > use NOKPROBE_SYMBOL() or nokprobe_inline for static-inline function.
> > (NOKPROBE_SYMBOL() will make the symbol non-inline always)
> 
> OK, should I make a note to change that in the arm64 port as well in a
> separate patch?

I think you don't need such note for this annotation. It should be fixed on arm64
too. (Sorry, that is my lazyness..)

[...]
> >> +
> >> +static void __kprobes kprobe_handler(struct pt_regs *regs)
> >> +{
> > 
> > Does this handler run under local IRQ disabled? (for making sure)
> 
> Exceptions are being handled with locals IRQs _enabled_.

Oops that's crazy and cool :D
So I guess it just implemented as an indirect jump referring the exception vector.
Just out of curiosity, is that enough safe for interruption?

> As we've not
> implemented any simulated instructions to modify the instruction
> pointer, I think this is safe? Then again, I'm new to this, so please
> bear with me.

kprobes itself should be safe, since I introduced a jump optimization,
which doing similar thing.

However, if it is not IRQ disabled, you must preempt_disable() right
before using get_kprobe_ctlblk() because it is per-cpu.

> >> +	struct kprobe *p, *cur_kprobe;
> >> +	struct kprobe_ctlblk *kcb;
> >> +	unsigned long addr = instruction_pointer(regs);
> >> +
> >> +	kcb = get_kprobe_ctlblk();
> >> +	cur_kprobe = kprobe_running();
> >> +
> >> +	p = get_kprobe((kprobe_opcode_t *) addr);
> >> +
> >> +	if (p) {
> >> +		if (cur_kprobe) {
> >> +			if (reenter_kprobe(p, regs, kcb))
> >> +				return;
> >> +		} else {
> >> +			/* Probe hit */
> >> +			set_current_kprobe(p);
> >> +			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> >> +
> >> +			/*
> >> +			 * If we have no pre-handler or it returned 0, we
> >> +			 * continue with normal processing.  If we have a
> >> +			 * pre-handler and it returned non-zero, it will
> >> +			 * modify the execution path and no need to single
> >> +			 * stepping. Let's just reset current kprobe and exit.
> >> +			 *
> >> +			 * pre_handler can hit a breakpoint and can step thru
> >> +			 * before return, keep PSTATE D-flag enabled until
> >> +			 * pre_handler return back.
> > 
> > Is this true on RISC-V too?
> 
> It's not as we don't have a debug-unit at the moment. I'll remove the
> second part of the comment block.

OK.

> >> +			 */
> >> +			if (!p->pre_handler || !p->pre_handler(p, regs))
> >> +				simulate(p, regs, kcb, 0);
> >> +			else
> >> +				reset_current_kprobe();
> >> +		}
> >> +	}
> >> +	/*
> >> +	 * The breakpoint instruction was removed right
> >> +	 * after we hit it.  Another cpu has removed
> >> +	 * either a probepoint or a debugger breakpoint
> >> +	 * at this address.  In either case, no further
> >> +	 * handling of this interrupt is appropriate.
> >> +	 * Return back to original instruction, and continue.
> >> +	 */
> > 
> > This should return 0 if it doesn't handle anything, but if it handles c.break
> > should return 1.
> 
> I thought so too, but didn't insert one because of the comment (again,
> copied from arm64). If get_kprobe doesn't return a result, it could have
> been removed between the time the exception got raised or is the comment
> just wrong? On the other hand, solving it this way effectively means
> that we'll silently drop any other exceptions.

Hmm, in x86, original code, I checked the *addr whether there is a Breakpoint
instruction. If not, this means someone already removed it. If there is,
we just return to kernel's break handler and see what happens, since the breakpoint
instruction can be used from another subsystem. If no one handles it, kernel may
warn it finds stray breakpoint. (warning such case is kernel's work, not kprobes') 

I think I have to recheck the arm64's implementation again...


> >> +}
> >> +
> >> +int __kprobes
> >> +kprobe_breakpoint_handler(struct pt_regs *regs)
> >> +{
> >> +	kprobe_handler(regs);
> >> +	return 1;
> > 
> > Why don't you call kprobe_handler directly?
> 
> I should.
> 
> > 
> >> +}
> >> +
> >> +bool arch_within_kprobe_blacklist(unsigned long addr)
> >> +{
> >> +	if ((addr >= (unsigned long)__kprobes_text_start &&
> >> +	    addr < (unsigned long)__kprobes_text_end) ||
> >> +	    (addr >= (unsigned long)__entry_text_start &&
> >> +	    addr < (unsigned long)__entry_text_end) ||
> >> +	    !!search_exception_tables(addr))
> >> +		return true;
> >> +
> >> +	return false;
> >> +}
> >> +
> >> +void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
> >> +{
> >> +	struct kretprobe_instance *ri = NULL;
> >> +	struct hlist_head *head, empty_rp;
> >> +	struct hlist_node *tmp;
> >> +	unsigned long flags, orig_ret_address = 0;
> >> +	unsigned long trampoline_address =
> >> +		(unsigned long)&kretprobe_trampoline;
> >> +	kprobe_opcode_t *correct_ret_addr = NULL;
> >> +
> > 
> > 	It seems you don't setup instruction_pointer.
> 
> I don't think I get what you mean by that. The instruction pointer (or
> rather the return address register) gets set by kretprobe_trampoline.S
> to the address returned from this function.

I meant regs->sepc should be set as the address of the trampoline function.
There is a histrical reason, but that is expected behavior...

[...]
> >> diff --git a/arch/riscv/kernel/probes/simulate-insn.c b/arch/riscv/kernel/probes/simulate-insn.c
> >> new file mode 100644
> >> index 000000000000..5734d9bae22f
> >> --- /dev/null
> >> +++ b/arch/riscv/kernel/probes/simulate-insn.c
> >> @@ -0,0 +1,33 @@
> >> +// SPDX-License-Identifier: GPL-2.0+
> >> +
> >> +#include <linux/bitops.h>
> >> +#include <linux/kernel.h>
> >> +#include <linux/kprobes.h>
> >> +
> >> +#include "simulate-insn.h"
> >> +
> >> +#define bit_at(value, bit)		((value) & (1 << (bit)))
> >> +#define move_bit_at(value, bit, to)	((bit_at(value, bit) >> bit) << to)
> >> +
> >> +void __kprobes
> >> +simulate_caddisp16(u32 opcode, long addr, struct pt_regs *regs)
> >> +{
> >> +	s16 imm;
> >> +
> >> +	/*
> >> +	 * Immediate value layout in c.addisp16:
> >> +	 * xxx9 xxxx x468 75xx
> >> +	 * 1  1    8    4    0
> >> +	 * 5  2
> >> +	 */
> >> +	imm = sign_extend32(
> >> +		move_bit_at(opcode, 12, 9) |
> >> +		move_bit_at(opcode, 6, 4) |
> >> +		move_bit_at(opcode, 5, 6) |
> >> +		move_bit_at(opcode, 4, 8) |
> >> +		move_bit_at(opcode, 3, 7) |
> >> +		move_bit_at(opcode, 2, 5),
> >> +		9);
> >> +
> >> +	regs->sp += imm;
> > 
> > What about updating regs->sepc?
> 
> sepc gets updated by instruction_pointer_set in kprobe_handler

post_kprobe_handler()? Anyway, I think it should be updated in
this function or simulate() since it is a part of instruction execution.

> >> +}
> >> diff --git a/arch/riscv/kernel/probes/simulate-insn.h b/arch/riscv/kernel/probes/simulate-insn.h
> >> new file mode 100644
> >> index 000000000000..dc2c06c30167
> >> --- /dev/null
> >> +++ b/arch/riscv/kernel/probes/simulate-insn.h
> >> @@ -0,0 +1,8 @@
> >> +/* SPDX-License-Identifier: GPL-2.0+ */
> >> +
> >> +#ifndef _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H
> >> +#define _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H
> >> +
> >> +void simulate_caddisp16(u32 opcode, long addr, struct pt_regs *regs);
> >> +
> >> +#endif /* _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H */
> >> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> >> index 24a9333dda2c..d7113178d401 100644
> >> --- a/arch/riscv/kernel/traps.c
> >> +++ b/arch/riscv/kernel/traps.c
> >> @@ -18,6 +18,7 @@
> >>  #include <linux/sched/signal.h>
> >>  #include <linux/signal.h>
> >>  #include <linux/kdebug.h>
> >> +#include <linux/kprobes.h>
> >>  #include <linux/uaccess.h>
> >>  #include <linux/mm.h>
> >>  #include <linux/module.h>
> >> @@ -120,8 +121,14 @@ DO_ERROR_INFO(do_trap_ecall_m,
> >>  
> >>  asmlinkage void do_trap_break(struct pt_regs *regs)
> >>  {
> >> +	bool handler_found = false;
> >> +
> >> +#ifdef CONFIG_KPROBES
> >> +	if (kprobe_breakpoint_handler(regs))
> >> +		handler_found = 1;
> > 
> > Why don't you just return from here?
> 
> Following the pattern I've seen in other places, I can change that.

Yeah, I think it's simpler.

And I found that the kprobe_breakpoint_handler() was called without
checking !user_mode(regs). In that case, you should add the check in
front of kprobe_breakpoint_handler() call.

Thank you,

-- 
Masami Hiramatsu <mhiramat@kernel.org>

^ permalink raw reply	[flat|nested] 18+ messages in thread

* Re: [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support
  2018-11-15  8:41       ` mhiramat
@ 2018-11-15  8:41         ` Masami Hiramatsu
  0 siblings, 0 replies; 18+ messages in thread
From: Masami Hiramatsu @ 2018-11-15  8:41 UTC (permalink / raw)
  To: Patrick Staehlin
  Cc: Albert Ou, Anders Roxell, Andrew Morton, Alan Kao,
	Catalin Marinas, Palmer Dabbelt, Will Deacon, linux-kernel,
	Al Viro, Souptick Joarder, Zong Li, Thomas Gleixner,
	Eric W. Biederman, linux-riscv, zhong jiang, Ingo Molnar,
	Luc Van Oostenryck, Jim Wilson

On Wed, 14 Nov 2018 21:52:57 +0100
Patrick Staehlin <me@packi.ch> wrote:

> Hi Masami,
> 
> thank you for your remarks.
> 
> On 14.11.18 09:37, Masami Hiramatsu wrote>
> > Thank you very much for implementing kprobes on RISC-V :)
> > 
> > On Tue, 13 Nov 2018 20:58:04 +0100
> > Patrick Stählin <me@packi.ch> wrote:
> > 
> >> First implementation, adapted from arm64. The C.ADDISP16 instruction
> >> gets simulated and the kprobes-handler called by inserting a C.EBREAK
> >> instruction.
> >>
> >> C.ADDISP16 was chosen as it sets-up the stack frame for functions.
> >> Some work has been done to support probes on non-compressed
> >> instructions but there is no support yet for decoding those.
> > 
> > Does this only support C.ADDISP16? No other insns are supported?
> > Supporting 1 insn is too few I think.
> 
> At the moment, yes. I'm waiting for some input from somebody with deeper
> insights into the RISC-V architecture than me before implementing more
> instructions, should solution I've chosen be woefully inadequate.

I think starting with a few emulatable set of instruction support is good
to me. But maybe we need more... 1 instruction is too limited.


> > Can RISC-V do single stepping? If not, we need to prepare emulator
> > as match as possible, or for ALU instructions, we can run it on
> > buffer and hook it.
> 
> The debug-specification is still a draft but there are some softcores
> that implement it. But even if it was finalized I don't think this will
> be made a mandatory extension so we need to simulate/emulate a good part
> of the instruction set anyway.

OK.

[...]
> >> diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c
> >> new file mode 100644
> >> index 000000000000..2d8f46f4c2e7
> >> --- /dev/null
> >> +++ b/arch/riscv/kernel/probes/decode-insn.c
> >> @@ -0,0 +1,38 @@
> >> +// SPDX-License-Identifier: GPL-2.0+
> >> +
> >> +#include <linux/kernel.h>
> >> +#include <linux/kprobes.h>
> >> +#include <linux/module.h>
> >> +#include <linux/kallsyms.h>
> >> +#include <asm/sections.h>
> >> +
> >> +#include "decode-insn.h"
> >> +#include "simulate-insn.h"
> >> +
> >> +#define C_ADDISP16_MASK 0x6F83
> >> +#define C_ADDISP16_VAL  0x6101
> >> +
> >> +/* Return:
> >> + *   INSN_REJECTED     If instruction is one not allowed to kprobe,
> >> + *   INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot.
> >> + */
> >> +enum probe_insn __kprobes
> >> +riscv_probe_decode_insn(kprobe_opcode_t *addr, struct arch_probe_insn *api)
> > 
> > Please don't use __kprobes anymore. That is old stlye, instead, please
> > use NOKPROBE_SYMBOL() or nokprobe_inline for static-inline function.
> > (NOKPROBE_SYMBOL() will make the symbol non-inline always)
> 
> OK, should I make a note to change that in the arm64 port as well in a
> separate patch?

I think you don't need such note for this annotation. It should be fixed on arm64
too. (Sorry, that is my lazyness..)

[...]
> >> +
> >> +static void __kprobes kprobe_handler(struct pt_regs *regs)
> >> +{
> > 
> > Does this handler run under local IRQ disabled? (for making sure)
> 
> Exceptions are being handled with locals IRQs _enabled_.

Oops that's crazy and cool :D
So I guess it just implemented as an indirect jump referring the exception vector.
Just out of curiosity, is that enough safe for interruption?

> As we've not
> implemented any simulated instructions to modify the instruction
> pointer, I think this is safe? Then again, I'm new to this, so please
> bear with me.

kprobes itself should be safe, since I introduced a jump optimization,
which doing similar thing.

However, if it is not IRQ disabled, you must preempt_disable() right
before using get_kprobe_ctlblk() because it is per-cpu.

> >> +	struct kprobe *p, *cur_kprobe;
> >> +	struct kprobe_ctlblk *kcb;
> >> +	unsigned long addr = instruction_pointer(regs);
> >> +
> >> +	kcb = get_kprobe_ctlblk();
> >> +	cur_kprobe = kprobe_running();
> >> +
> >> +	p = get_kprobe((kprobe_opcode_t *) addr);
> >> +
> >> +	if (p) {
> >> +		if (cur_kprobe) {
> >> +			if (reenter_kprobe(p, regs, kcb))
> >> +				return;
> >> +		} else {
> >> +			/* Probe hit */
> >> +			set_current_kprobe(p);
> >> +			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> >> +
> >> +			/*
> >> +			 * If we have no pre-handler or it returned 0, we
> >> +			 * continue with normal processing.  If we have a
> >> +			 * pre-handler and it returned non-zero, it will
> >> +			 * modify the execution path and no need to single
> >> +			 * stepping. Let's just reset current kprobe and exit.
> >> +			 *
> >> +			 * pre_handler can hit a breakpoint and can step thru
> >> +			 * before return, keep PSTATE D-flag enabled until
> >> +			 * pre_handler return back.
> > 
> > Is this true on RISC-V too?
> 
> It's not as we don't have a debug-unit at the moment. I'll remove the
> second part of the comment block.

OK.

> >> +			 */
> >> +			if (!p->pre_handler || !p->pre_handler(p, regs))
> >> +				simulate(p, regs, kcb, 0);
> >> +			else
> >> +				reset_current_kprobe();
> >> +		}
> >> +	}
> >> +	/*
> >> +	 * The breakpoint instruction was removed right
> >> +	 * after we hit it.  Another cpu has removed
> >> +	 * either a probepoint or a debugger breakpoint
> >> +	 * at this address.  In either case, no further
> >> +	 * handling of this interrupt is appropriate.
> >> +	 * Return back to original instruction, and continue.
> >> +	 */
> > 
> > This should return 0 if it doesn't handle anything, but if it handles c.break
> > should return 1.
> 
> I thought so too, but didn't insert one because of the comment (again,
> copied from arm64). If get_kprobe doesn't return a result, it could have
> been removed between the time the exception got raised or is the comment
> just wrong? On the other hand, solving it this way effectively means
> that we'll silently drop any other exceptions.

Hmm, in x86, original code, I checked the *addr whether there is a Breakpoint
instruction. If not, this means someone already removed it. If there is,
we just return to kernel's break handler and see what happens, since the breakpoint
instruction can be used from another subsystem. If no one handles it, kernel may
warn it finds stray breakpoint. (warning such case is kernel's work, not kprobes') 

I think I have to recheck the arm64's implementation again...


> >> +}
> >> +
> >> +int __kprobes
> >> +kprobe_breakpoint_handler(struct pt_regs *regs)
> >> +{
> >> +	kprobe_handler(regs);
> >> +	return 1;
> > 
> > Why don't you call kprobe_handler directly?
> 
> I should.
> 
> > 
> >> +}
> >> +
> >> +bool arch_within_kprobe_blacklist(unsigned long addr)
> >> +{
> >> +	if ((addr >= (unsigned long)__kprobes_text_start &&
> >> +	    addr < (unsigned long)__kprobes_text_end) ||
> >> +	    (addr >= (unsigned long)__entry_text_start &&
> >> +	    addr < (unsigned long)__entry_text_end) ||
> >> +	    !!search_exception_tables(addr))
> >> +		return true;
> >> +
> >> +	return false;
> >> +}
> >> +
> >> +void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
> >> +{
> >> +	struct kretprobe_instance *ri = NULL;
> >> +	struct hlist_head *head, empty_rp;
> >> +	struct hlist_node *tmp;
> >> +	unsigned long flags, orig_ret_address = 0;
> >> +	unsigned long trampoline_address =
> >> +		(unsigned long)&kretprobe_trampoline;
> >> +	kprobe_opcode_t *correct_ret_addr = NULL;
> >> +
> > 
> > 	It seems you don't setup instruction_pointer.
> 
> I don't think I get what you mean by that. The instruction pointer (or
> rather the return address register) gets set by kretprobe_trampoline.S
> to the address returned from this function.

I meant regs->sepc should be set as the address of the trampoline function.
There is a histrical reason, but that is expected behavior...

[...]
> >> diff --git a/arch/riscv/kernel/probes/simulate-insn.c b/arch/riscv/kernel/probes/simulate-insn.c
> >> new file mode 100644
> >> index 000000000000..5734d9bae22f
> >> --- /dev/null
> >> +++ b/arch/riscv/kernel/probes/simulate-insn.c
> >> @@ -0,0 +1,33 @@
> >> +// SPDX-License-Identifier: GPL-2.0+
> >> +
> >> +#include <linux/bitops.h>
> >> +#include <linux/kernel.h>
> >> +#include <linux/kprobes.h>
> >> +
> >> +#include "simulate-insn.h"
> >> +
> >> +#define bit_at(value, bit)		((value) & (1 << (bit)))
> >> +#define move_bit_at(value, bit, to)	((bit_at(value, bit) >> bit) << to)
> >> +
> >> +void __kprobes
> >> +simulate_caddisp16(u32 opcode, long addr, struct pt_regs *regs)
> >> +{
> >> +	s16 imm;
> >> +
> >> +	/*
> >> +	 * Immediate value layout in c.addisp16:
> >> +	 * xxx9 xxxx x468 75xx
> >> +	 * 1  1    8    4    0
> >> +	 * 5  2
> >> +	 */
> >> +	imm = sign_extend32(
> >> +		move_bit_at(opcode, 12, 9) |
> >> +		move_bit_at(opcode, 6, 4) |
> >> +		move_bit_at(opcode, 5, 6) |
> >> +		move_bit_at(opcode, 4, 8) |
> >> +		move_bit_at(opcode, 3, 7) |
> >> +		move_bit_at(opcode, 2, 5),
> >> +		9);
> >> +
> >> +	regs->sp += imm;
> > 
> > What about updating regs->sepc?
> 
> sepc gets updated by instruction_pointer_set in kprobe_handler

post_kprobe_handler()? Anyway, I think it should be updated in
this function or simulate() since it is a part of instruction execution.

> >> +}
> >> diff --git a/arch/riscv/kernel/probes/simulate-insn.h b/arch/riscv/kernel/probes/simulate-insn.h
> >> new file mode 100644
> >> index 000000000000..dc2c06c30167
> >> --- /dev/null
> >> +++ b/arch/riscv/kernel/probes/simulate-insn.h
> >> @@ -0,0 +1,8 @@
> >> +/* SPDX-License-Identifier: GPL-2.0+ */
> >> +
> >> +#ifndef _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H
> >> +#define _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H
> >> +
> >> +void simulate_caddisp16(u32 opcode, long addr, struct pt_regs *regs);
> >> +
> >> +#endif /* _RISCV_KERNEL_KPROBES_SIMULATE_INSN_H */
> >> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> >> index 24a9333dda2c..d7113178d401 100644
> >> --- a/arch/riscv/kernel/traps.c
> >> +++ b/arch/riscv/kernel/traps.c
> >> @@ -18,6 +18,7 @@
> >>  #include <linux/sched/signal.h>
> >>  #include <linux/signal.h>
> >>  #include <linux/kdebug.h>
> >> +#include <linux/kprobes.h>
> >>  #include <linux/uaccess.h>
> >>  #include <linux/mm.h>
> >>  #include <linux/module.h>
> >> @@ -120,8 +121,14 @@ DO_ERROR_INFO(do_trap_ecall_m,
> >>  
> >>  asmlinkage void do_trap_break(struct pt_regs *regs)
> >>  {
> >> +	bool handler_found = false;
> >> +
> >> +#ifdef CONFIG_KPROBES
> >> +	if (kprobe_breakpoint_handler(regs))
> >> +		handler_found = 1;
> > 
> > Why don't you just return from here?
> 
> Following the pattern I've seen in other places, I can change that.

Yeah, I think it's simpler.

And I found that the kprobe_breakpoint_handler() was called without
checking !user_mode(regs). In that case, you should add the check in
front of kprobe_breakpoint_handler() call.

Thank you,

-- 
Masami Hiramatsu <mhiramat@kernel.org>

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^ permalink raw reply	[flat|nested] 18+ messages in thread

end of thread, back to index

Thread overview: 18+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-11-13 19:58 [RFC/RFT 0/2] RISC-V: kprobes/kretprobe support me
2018-11-13 19:58 ` Patrick Stählin
2018-11-13 19:58 ` [RFC/RFT 1/2] RISC-V: Implement ptrace regs and stack API me
2018-11-13 19:58   ` Patrick Stählin
2018-11-13 19:58 ` [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support me
2018-11-13 19:58   ` Patrick Stählin
2018-11-14  8:37   ` mhiramat
2018-11-14  8:37     ` Masami Hiramatsu
2018-11-14 15:49     ` mhiramat
2018-11-14 15:49       ` Masami Hiramatsu
2018-11-14 21:10       ` me
2018-11-14 21:10         ` Patrick Staehlin
2018-11-15  7:50         ` mhiramat
2018-11-15  7:50           ` Masami Hiramatsu
2018-11-14 20:52     ` me
2018-11-14 20:52       ` Patrick Staehlin
2018-11-15  8:41       ` mhiramat
2018-11-15  8:41         ` Masami Hiramatsu

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