Re: [PATCH 1/3] riscv: add required functions to enable HAVE_REGS_AND_STACK_ACCESS_API

[Paul Walmsley <paul.walmsley@sifive.com>]

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On Thu, 21 Nov 2019, Paul Walmsley wrote:

> As I understand it, this patch hasn't been signed off on by Patrick.
> I've sent him an E-mail asking him whether he's willing to add his 
> Signed-off-by:, but haven't heard back from it.
> 
> From our discussions, I understand that this patch is based partially on 
> some of his earlier, public, kprobes work.  In lieu of any response from 
> Patrick, could you please resend this patch and just note in the commit 
> description that it's partially based on one of his patches, add a Link: 
> line that points to the URL of the patch that it's partially based on, and 
> replace the Signed-off-by: with a Co-developed-by: or something similar?

OK - just looked at the patches more closely, and I think I see what's 
going on here.  This patch looks like a rebased version of this patch:

https://lore.kernel.org/linux-riscv/20181113195804.22825-2-me@packi.ch/

So let's just plan to use an updated version of Patrick's original 
(below).  Please let me know if you have any comments on it or if I 
missed something -


- Paul

From: Patrick Stählin <me@packi.ch>
Date: Tue, 13 Nov 2018 20:58:03 +0100
Subject: [PATCH] RISC-V: Implement ptrace regs and stack API
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Needed for kprobes support. Copied and adapted from arm64 code.

Signed-off-by: Patrick Stählin <me@packi.ch>
[paul.walmsley@sifive.com: updated to apply; fixed checkpatch issues;
 fixed regs_get_register() kerneldoc]
Cc: Vincent Chen <vincent.chen@sifive.com>
Link: https://lore.kernel.org/linux-riscv/20181113195803.CjtBCsUcG9czwiqmPBGKUjvl5Ojxq2SIPaioQUHXFI0@z/
Link: https://lore.kernel.org/linux-riscv/1572919114-3886-1-git-send-email-vincent.chen@sifive.com/T/#mdb346527d25ea1959ab57ff9d1c056bcd29c7172
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
---
 arch/riscv/Kconfig              |  1 +
 arch/riscv/include/asm/ptrace.h | 30 ++++++++++
 arch/riscv/kernel/ptrace.c      | 99 +++++++++++++++++++++++++++++++++
 3 files changed, 130 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 8eebbc8860bb..d5bbf4223fd2 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -61,6 +61,7 @@ config RISCV
 	select SPARSEMEM_STATIC if 32BIT
 	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
 	select HAVE_ARCH_MMAP_RND_BITS
+	select HAVE_REGS_AND_STACK_ACCESS_API
 
 config ARCH_MMAP_RND_BITS_MIN
 	default 18 if 64BIT
diff --git a/arch/riscv/include/asm/ptrace.h b/arch/riscv/include/asm/ptrace.h
index d48d1e13973c..50d37b123a61 100644
--- a/arch/riscv/include/asm/ptrace.h
+++ b/arch/riscv/include/asm/ptrace.h
@@ -8,6 +8,7 @@
 
 #include <uapi/asm/ptrace.h>
 #include <asm/csr.h>
+#include <linux/compiler.h>
 
 #ifndef __ASSEMBLY__
 
@@ -60,6 +61,7 @@ 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 */
 static inline unsigned long instruction_pointer(struct pt_regs *regs)
@@ -85,6 +87,12 @@ static inline void user_stack_pointer_set(struct pt_regs *regs,
 	regs->sp =  val;
 }
 
+/* Valid only for Kernel mode traps. */
+static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
+{
+	return regs->sp;
+}
+
 /* Helpers for working with the frame pointer */
 static inline unsigned long frame_pointer(struct pt_regs *regs)
 {
@@ -101,6 +109,28 @@ static inline unsigned long regs_return_value(struct pt_regs *regs)
 	return regs->a0;
 }
 
+int regs_query_register_offset(const char *name);
+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 from @regs of a register
+ * identified by @offset.  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 1252113ef8b2..5076b30fe18b 100644
--- a/arch/riscv/kernel/ptrace.c
+++ b/arch/riscv/kernel/ptrace.c
@@ -125,6 +125,105 @@ 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; 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);
-- 
2.24.0.rc0