[RFC][PATCH 0/3 v3] ftrace: Add access to function arguments for all callbacks

[RFC][PATCH 0/3 v3] ftrace: Add access to function arguments for all callbacks

[Steven Rostedt]

This is something I wanted to implement a long time ago, but held off until
there was a good reason to do so. Now it appears that having access to the
arguments of the function by default is very useful. As a bonus, because
arguments must be saved regardless before calling a callback, because they
need to be restored before returning back to the start of the traced
function, there's not much work to do to have them always be there for
normal function callbacks.

The basic idea is that if CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS is set, then
all callbacks registered to ftrace can use the regs parameter for the stack
and arguments (kernel_stack_pointer(regs), regs_get_kernel_argument(regs, n)),
without the need to set REGS that causes overhead by saving all registers as
REGS simulates a breakpoint.

This could be extended to move the REGS portion to kprobes itself, and
remove the SAVE_REGS flag completely, but for now, kprobes still uses the
full SAVE_REGS support.

The last patch extends the WITH_ARGS to allow default function tracing to
modify the instruction pointer, where livepatching for x86 no longer needs
to save all registers.

The idea of this approach is to give enough information to a callback that
it could retrieve all arguments, which includes the stack pointer and
instruction pointer.

This can also be extended to modify the function graph tracer to use the
function tracer instead of having a separate trampoline.

Changes since v2:

 - Change all callback args to use struct ftrace_regs, and if something
   requires the full regs, it must use the ftrace_get_regs() helper macro,
   which will return NULL if the regs isn't full (FL_SAVE_REGS set).
   This addresses a concern by both Peter Zijlsta and Thomas Gleixner that
   a partially filled pt_regs may be used inappropriately.

 - No test patch in this version.

 - Use case using livepatching is added. This passes the test_livepatch.sh
   selftest.

Steven Rostedt (VMware) (3):
      ftrace: Have the callbacks receive a struct ftrace_regs instead of pt_regs
      ftrace/x86: Allow for arguments to be passed in to ftrace_regs by default
      livepatching: Use the default ftrace_ops instead of REGS when ARGS is available

----
 arch/powerpc/include/asm/livepatch.h |  4 +++-
 arch/s390/include/asm/livepatch.h    |  5 ++++-
 arch/x86/Kconfig                     |  1 +
 arch/x86/include/asm/ftrace.h        | 18 ++++++++++++++++++
 arch/x86/include/asm/livepatch.h     |  4 ++--
 arch/x86/kernel/ftrace_64.S          | 15 +++++++++++++--
 arch/x86/kernel/kprobes/ftrace.c     |  3 ++-
 include/linux/ftrace.h               | 28 ++++++++++++++++++++++++++--
 include/linux/kprobes.h              |  2 +-
 kernel/livepatch/patch.c             | 10 ++++++----
 kernel/trace/Kconfig                 |  9 +++++++++
 kernel/trace/ftrace.c                | 27 +++++++++++++++------------
 kernel/trace/trace_event_perf.c      |  2 +-
 kernel/trace/trace_functions.c       |  9 ++++-----
 kernel/trace/trace_irqsoff.c         |  2 +-
 kernel/trace/trace_sched_wakeup.c    |  2 +-
 kernel/trace/trace_selftest.c        | 20 +++++++++++---------
 kernel/trace/trace_stack.c           |  2 +-
 18 files changed, 119 insertions(+), 44 deletions(-)

[RFC][PATCH 1/3 v3] ftrace: Have the callbacks receive a struct ftrace_regs instead of pt_regs

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

In preparation to have arguments of a function passed to callbacks attached
to functions as default, change the default callback prototype to receive a
struct ftrace_regs as the forth parameter instead of a pt_regs.

For callbacks that set the FL_SAVE_REGS flag in their ftrace_ops flags, they
will now need to get the pt_regs via a ftrace_get_regs() helper call. If
this is called by a callback that their ftrace_ops did not have a
FL_SAVE_REGS flag set, it that helper function will return NULL.

This will allow the ftrace_regs to hold enough just to get the parameters
and stack pointer, but without the worry that callbacks may have a pt_regs
that is not completely filled.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 arch/x86/kernel/kprobes/ftrace.c  |  3 ++-
 include/linux/ftrace.h            | 16 ++++++++++++++--
 include/linux/kprobes.h           |  2 +-
 kernel/livepatch/patch.c          |  3 ++-
 kernel/trace/ftrace.c             | 27 +++++++++++++++------------
 kernel/trace/trace_event_perf.c   |  2 +-
 kernel/trace/trace_functions.c    |  9 ++++-----
 kernel/trace/trace_irqsoff.c      |  2 +-
 kernel/trace/trace_sched_wakeup.c |  2 +-
 kernel/trace/trace_selftest.c     | 20 +++++++++++---------
 kernel/trace/trace_stack.c        |  2 +-
 11 files changed, 53 insertions(+), 35 deletions(-)

diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c
index a40a6cdfcca3..a01849ffe013 100644
--- a/arch/x86/kernel/kprobes/ftrace.c
+++ b/arch/x86/kernel/kprobes/ftrace.c
@@ -14,8 +14,9 @@
 
 /* Ftrace callback handler for kprobes -- called under preepmt disabed */
 void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
-			   struct ftrace_ops *ops, struct pt_regs *regs)
+			   struct ftrace_ops *ops, struct ftrace_regs *fregs)
 {
+	struct pt_regs *regs = ftrace_get_regs(fregs);
 	struct kprobe *p;
 	struct kprobe_ctlblk *kcb;
 	int bit;
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 8dde9c17aaa5..24e1fa52337d 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -90,8 +90,20 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
 
 struct ftrace_ops;
 
+struct ftrace_regs {
+	struct pt_regs		regs;
+};
+
+static __always_inline struct pt_regs *ftrace_get_regs(struct ftrace_regs *fregs)
+{
+	if (!fregs)
+		return NULL;
+
+	return &fregs->regs;
+}
+
 typedef void (*ftrace_func_t)(unsigned long ip, unsigned long parent_ip,
-			      struct ftrace_ops *op, struct pt_regs *regs);
+			      struct ftrace_ops *op, struct ftrace_regs *fregs);
 
 ftrace_func_t ftrace_ops_get_func(struct ftrace_ops *ops);
 
@@ -259,7 +271,7 @@ int register_ftrace_function(struct ftrace_ops *ops);
 int unregister_ftrace_function(struct ftrace_ops *ops);
 
 extern void ftrace_stub(unsigned long a0, unsigned long a1,
-			struct ftrace_ops *op, struct pt_regs *regs);
+			struct ftrace_ops *op, struct ftrace_regs *fregs);
 
 #else /* !CONFIG_FUNCTION_TRACER */
 /*
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 8aab327b5539..5ac1d9b1d58c 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -325,7 +325,7 @@ static inline void wait_for_kprobe_optimizer(void) { }
 #endif /* CONFIG_OPTPROBES */
 #ifdef CONFIG_KPROBES_ON_FTRACE
 extern void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
-				  struct ftrace_ops *ops, struct pt_regs *regs);
+				  struct ftrace_ops *ops, struct ftrace_regs *fregs);
 extern int arch_prepare_kprobe_ftrace(struct kprobe *p);
 #endif
 
diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
index 6c0164d24bbd..9af0a7c8a255 100644
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c
@@ -40,8 +40,9 @@ struct klp_ops *klp_find_ops(void *old_func)
 static void notrace klp_ftrace_handler(unsigned long ip,
 				       unsigned long parent_ip,
 				       struct ftrace_ops *fops,
-				       struct pt_regs *regs)
+				       struct ftrace_regs *fregs)
 {
+	struct pt_regs *regs = ftrace_get_regs(fregs);
 	struct klp_ops *ops;
 	struct klp_func *func;
 	int patch_state;
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 2dcae8251104..7ef9048b3d1e 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -121,7 +121,7 @@ struct ftrace_ops global_ops;
 
 #if ARCH_SUPPORTS_FTRACE_OPS
 static void ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
-				 struct ftrace_ops *op, struct pt_regs *regs);
+				 struct ftrace_ops *op, struct ftrace_regs *fregs);
 #else
 /* See comment below, where ftrace_ops_list_func is defined */
 static void ftrace_ops_no_ops(unsigned long ip, unsigned long parent_ip);
@@ -140,7 +140,7 @@ static inline void ftrace_ops_init(struct ftrace_ops *ops)
 }
 
 static void ftrace_pid_func(unsigned long ip, unsigned long parent_ip,
-			    struct ftrace_ops *op, struct pt_regs *regs)
+			    struct ftrace_ops *op, struct ftrace_regs *fregs)
 {
 	struct trace_array *tr = op->private;
 	int pid;
@@ -154,7 +154,7 @@ static void ftrace_pid_func(unsigned long ip, unsigned long parent_ip,
 			return;
 	}
 
-	op->saved_func(ip, parent_ip, op, regs);
+	op->saved_func(ip, parent_ip, op, fregs);
 }
 
 static void ftrace_sync_ipi(void *data)
@@ -754,7 +754,7 @@ ftrace_profile_alloc(struct ftrace_profile_stat *stat, unsigned long ip)
 
 static void
 function_profile_call(unsigned long ip, unsigned long parent_ip,
-		      struct ftrace_ops *ops, struct pt_regs *regs)
+		      struct ftrace_ops *ops, struct ftrace_regs *fregs)
 {
 	struct ftrace_profile_stat *stat;
 	struct ftrace_profile *rec;
@@ -2143,6 +2143,7 @@ static int ftrace_check_record(struct dyn_ftrace *rec, bool enable, bool update)
 				else
 					rec->flags &= ~FTRACE_FL_TRAMP_EN;
 			}
+
 			if (flag & FTRACE_FL_DIRECT) {
 				/*
 				 * If there's only one user (direct_ops helper)
@@ -2368,8 +2369,9 @@ unsigned long ftrace_find_rec_direct(unsigned long ip)
 }
 
 static void call_direct_funcs(unsigned long ip, unsigned long pip,
-			      struct ftrace_ops *ops, struct pt_regs *regs)
+			      struct ftrace_ops *ops, struct ftrace_regs *fregs)
 {
+	struct pt_regs *regs = ftrace_get_regs(fregs);
 	unsigned long addr;
 
 	addr = ftrace_find_rec_direct(ip);
@@ -4293,7 +4295,7 @@ static int __init ftrace_mod_cmd_init(void)
 core_initcall(ftrace_mod_cmd_init);
 
 static void function_trace_probe_call(unsigned long ip, unsigned long parent_ip,
-				      struct ftrace_ops *op, struct pt_regs *pt_regs)
+				      struct ftrace_ops *op, struct ftrace_regs *fregs)
 {
 	struct ftrace_probe_ops *probe_ops;
 	struct ftrace_func_probe *probe;
@@ -6913,8 +6915,9 @@ void ftrace_reset_array_ops(struct trace_array *tr)
 
 static nokprobe_inline void
 __ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
-		       struct ftrace_ops *ignored, struct pt_regs *regs)
+		       struct ftrace_ops *ignored, struct ftrace_regs *fregs)
 {
+	struct pt_regs *regs = ftrace_get_regs(fregs);
 	struct ftrace_ops *op;
 	int bit;
 
@@ -6947,7 +6950,7 @@ __ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
 				pr_warn("op=%p %pS\n", op, op);
 				goto out;
 			}
-			op->func(ip, parent_ip, op, regs);
+			op->func(ip, parent_ip, op, fregs);
 		}
 	} while_for_each_ftrace_op(op);
 out:
@@ -6970,9 +6973,9 @@ __ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
  */
 #if ARCH_SUPPORTS_FTRACE_OPS
 static void ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
-				 struct ftrace_ops *op, struct pt_regs *regs)
+				 struct ftrace_ops *op, struct ftrace_regs *fregs)
 {
-	__ftrace_ops_list_func(ip, parent_ip, NULL, regs);
+	__ftrace_ops_list_func(ip, parent_ip, NULL, fregs);
 }
 NOKPROBE_SYMBOL(ftrace_ops_list_func);
 #else
@@ -6989,7 +6992,7 @@ NOKPROBE_SYMBOL(ftrace_ops_no_ops);
  * this function will be called by the mcount trampoline.
  */
 static void ftrace_ops_assist_func(unsigned long ip, unsigned long parent_ip,
-				   struct ftrace_ops *op, struct pt_regs *regs)
+				   struct ftrace_ops *op, struct ftrace_regs *fregs)
 {
 	int bit;
 
@@ -7002,7 +7005,7 @@ static void ftrace_ops_assist_func(unsigned long ip, unsigned long parent_ip,
 
 	preempt_disable_notrace();
 
-	op->func(ip, parent_ip, op, regs);
+	op->func(ip, parent_ip, op, fregs);
 
 	preempt_enable_notrace();
 	trace_clear_recursion(bit);
diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index a2b9fddb8148..86b7cdff1403 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -432,7 +432,7 @@ NOKPROBE_SYMBOL(perf_trace_buf_update);
 #ifdef CONFIG_FUNCTION_TRACER
 static void
 perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip,
-			  struct ftrace_ops *ops, struct pt_regs *pt_regs)
+			  struct ftrace_ops *ops,  struct ftrace_regs *fregs)
 {
 	struct ftrace_entry *entry;
 	struct perf_event *event;
diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index 89c414ce1388..9f88de3f1d47 100644
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -23,10 +23,10 @@ static void tracing_start_function_trace(struct trace_array *tr);
 static void tracing_stop_function_trace(struct trace_array *tr);
 static void
 function_trace_call(unsigned long ip, unsigned long parent_ip,
-		    struct ftrace_ops *op, struct pt_regs *pt_regs);
+		    struct ftrace_ops *op, struct ftrace_regs *fregs);
 static void
 function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
-			  struct ftrace_ops *op, struct pt_regs *pt_regs);
+			  struct ftrace_ops *op, struct ftrace_regs *fregs);
 static struct tracer_flags func_flags;
 
 /* Our option */
@@ -89,7 +89,6 @@ void ftrace_destroy_function_files(struct trace_array *tr)
 static int function_trace_init(struct trace_array *tr)
 {
 	ftrace_func_t func;
-
 	/*
 	 * Instance trace_arrays get their ops allocated
 	 * at instance creation. Unless it failed
@@ -129,7 +128,7 @@ static void function_trace_start(struct trace_array *tr)
 
 static void
 function_trace_call(unsigned long ip, unsigned long parent_ip,
-		    struct ftrace_ops *op, struct pt_regs *pt_regs)
+		    struct ftrace_ops *op, struct ftrace_regs *fregs)
 {
 	struct trace_array *tr = op->private;
 	struct trace_array_cpu *data;
@@ -178,7 +177,7 @@ function_trace_call(unsigned long ip, unsigned long parent_ip,
 
 static void
 function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
-			  struct ftrace_ops *op, struct pt_regs *pt_regs)
+			  struct ftrace_ops *op, struct ftrace_regs *fregs)
 {
 	struct trace_array *tr = op->private;
 	struct trace_array_cpu *data;
diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index 10bbb0f381d5..d06aab4dcbb8 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -138,7 +138,7 @@ static int func_prolog_dec(struct trace_array *tr,
  */
 static void
 irqsoff_tracer_call(unsigned long ip, unsigned long parent_ip,
-		    struct ftrace_ops *op, struct pt_regs *pt_regs)
+		    struct ftrace_ops *op, struct ftrace_regs *fregs)
 {
 	struct trace_array *tr = irqsoff_trace;
 	struct trace_array_cpu *data;
diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
index 97b10bb31a1f..c0181066dbe9 100644
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -212,7 +212,7 @@ static void wakeup_print_header(struct seq_file *s)
  */
 static void
 wakeup_tracer_call(unsigned long ip, unsigned long parent_ip,
-		   struct ftrace_ops *op, struct pt_regs *pt_regs)
+		   struct ftrace_ops *op, struct ftrace_regs *fregs)
 {
 	struct trace_array *tr = wakeup_trace;
 	struct trace_array_cpu *data;
diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
index 50dd913d23e7..23f07370f40e 100644
--- a/kernel/trace/trace_selftest.c
+++ b/kernel/trace/trace_selftest.c
@@ -107,7 +107,7 @@ static int trace_selftest_test_probe1_cnt;
 static void trace_selftest_test_probe1_func(unsigned long ip,
 					    unsigned long pip,
 					    struct ftrace_ops *op,
-					    struct pt_regs *pt_regs)
+					    struct ftrace_regs *fregs)
 {
 	trace_selftest_test_probe1_cnt++;
 }
@@ -116,7 +116,7 @@ static int trace_selftest_test_probe2_cnt;
 static void trace_selftest_test_probe2_func(unsigned long ip,
 					    unsigned long pip,
 					    struct ftrace_ops *op,
-					    struct pt_regs *pt_regs)
+					    struct ftrace_regs *fregs)
 {
 	trace_selftest_test_probe2_cnt++;
 }
@@ -125,7 +125,7 @@ static int trace_selftest_test_probe3_cnt;
 static void trace_selftest_test_probe3_func(unsigned long ip,
 					    unsigned long pip,
 					    struct ftrace_ops *op,
-					    struct pt_regs *pt_regs)
+					    struct ftrace_regs *fregs)
 {
 	trace_selftest_test_probe3_cnt++;
 }
@@ -134,7 +134,7 @@ static int trace_selftest_test_global_cnt;
 static void trace_selftest_test_global_func(unsigned long ip,
 					    unsigned long pip,
 					    struct ftrace_ops *op,
-					    struct pt_regs *pt_regs)
+					    struct ftrace_regs *fregs)
 {
 	trace_selftest_test_global_cnt++;
 }
@@ -143,7 +143,7 @@ static int trace_selftest_test_dyn_cnt;
 static void trace_selftest_test_dyn_func(unsigned long ip,
 					 unsigned long pip,
 					 struct ftrace_ops *op,
-					 struct pt_regs *pt_regs)
+					 struct ftrace_regs *fregs)
 {
 	trace_selftest_test_dyn_cnt++;
 }
@@ -414,7 +414,7 @@ static int trace_selftest_recursion_cnt;
 static void trace_selftest_test_recursion_func(unsigned long ip,
 					       unsigned long pip,
 					       struct ftrace_ops *op,
-					       struct pt_regs *pt_regs)
+					       struct ftrace_regs *fregs)
 {
 	/*
 	 * This function is registered without the recursion safe flag.
@@ -429,7 +429,7 @@ static void trace_selftest_test_recursion_func(unsigned long ip,
 static void trace_selftest_test_recursion_safe_func(unsigned long ip,
 						    unsigned long pip,
 						    struct ftrace_ops *op,
-						    struct pt_regs *pt_regs)
+						    struct ftrace_regs *fregs)
 {
 	/*
 	 * We said we would provide our own recursion. By calling
@@ -543,9 +543,11 @@ static enum {
 static void trace_selftest_test_regs_func(unsigned long ip,
 					  unsigned long pip,
 					  struct ftrace_ops *op,
-					  struct pt_regs *pt_regs)
+					  struct ftrace_regs *fregs)
 {
-	if (pt_regs)
+	struct pt_regs *regs = ftrace_get_regs(fregs);
+
+	if (regs)
 		trace_selftest_regs_stat = TRACE_SELFTEST_REGS_FOUND;
 	else
 		trace_selftest_regs_stat = TRACE_SELFTEST_REGS_NOT_FOUND;
diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 969db526a563..63c285042051 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -290,7 +290,7 @@ static void check_stack(unsigned long ip, unsigned long *stack)
 
 static void
 stack_trace_call(unsigned long ip, unsigned long parent_ip,
-		 struct ftrace_ops *op, struct pt_regs *pt_regs)
+		 struct ftrace_ops *op, struct ftrace_regs *fregs)
 {
 	unsigned long stack;
 
-- 
2.28.0

[RFC][PATCH 2/3 v3] ftrace/x86: Allow for arguments to be passed in to ftrace_regs by default

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

Currently, the only way to get access to the registers of a function via a
ftrace callback is to set the "FL_SAVE_REGS" bit in the ftrace_ops. But as this
saves all regs as if a breakpoint were to trigger (for use with kprobes), it
is expensive.

The regs are already saved on the stack for the default ftrace callbacks, as
that is required otherwise a function being traced will get the wrong
arguments and possibly crash. And on x86, the arguments are already stored
where they would be on a pt_regs structure to use that code for both the
regs version of a callback, it makes sense to pass that information always
to all functions.

If an architecture does this (as x86_64 now does), it is to set
HAVE_DYNAMIC_FTRACE_WITH_ARGS, and this will let the generic code that it
could have access to arguments without having to set the flags.

This also includes having the stack pointer being saved, which could be used
for accessing arguments on the stack, as well as having the function graph
tracer not require its own trampoline!

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 arch/x86/Kconfig              |  1 +
 arch/x86/include/asm/ftrace.h | 15 +++++++++++++++
 arch/x86/kernel/ftrace_64.S   | 11 +++++++++--
 include/linux/ftrace.h        |  7 ++++++-
 kernel/trace/Kconfig          |  9 +++++++++
 5 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7101ac64bb20..b4d2b1fcfd09 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -167,6 +167,7 @@ config X86
 	select HAVE_DMA_CONTIGUOUS
 	select HAVE_DYNAMIC_FTRACE
 	select HAVE_DYNAMIC_FTRACE_WITH_REGS
+	select HAVE_DYNAMIC_FTRACE_WITH_ARGS	if X86_64
 	select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 	select HAVE_EBPF_JIT
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS
diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
index 84b9449be080..6b175c2468e6 100644
--- a/arch/x86/include/asm/ftrace.h
+++ b/arch/x86/include/asm/ftrace.h
@@ -49,6 +49,21 @@ struct dyn_arch_ftrace {
 
 #define FTRACE_GRAPH_TRAMP_ADDR FTRACE_GRAPH_ADDR
 
+#ifdef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
+struct ftrace_regs {
+	struct pt_regs		regs;
+};
+
+static __always_inline struct pt_regs *
+arch_ftrace_get_regs(struct ftrace_regs *fregs)
+{
+	/* Only when FL_SAVE_REGS is set, cs will be non zero */
+	if (!fregs->regs.cs)
+		return NULL;
+	return &fregs->regs;
+}
+#endif
+
 #endif /*  CONFIG_DYNAMIC_FTRACE */
 #endif /* __ASSEMBLY__ */
 #endif /* CONFIG_FUNCTION_TRACER */
diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index ac3d5f22fe64..c4177bd00cd2 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -140,12 +140,19 @@ SYM_FUNC_START(ftrace_caller)
 	/* save_mcount_regs fills in first two parameters */
 	save_mcount_regs
 
+	/* Stack - skipping return address and flags */
+	leaq MCOUNT_REG_SIZE+8(%rsp), %rcx
+	movq %rcx, RSP(%rsp)
+
 SYM_INNER_LABEL(ftrace_caller_op_ptr, SYM_L_GLOBAL)
 	/* Load the ftrace_ops into the 3rd parameter */
 	movq function_trace_op(%rip), %rdx
 
-	/* regs go into 4th parameter (but make it NULL) */
-	movq $0, %rcx
+	/* regs go into 4th parameter */
+	leaq (%rsp), %rcx
+
+	/* Only ops with REGS flag set should have RIP set */
+	movq $0, CS(%rsp)
 
 SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
 	call ftrace_stub
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 24e1fa52337d..588ea7023a7a 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -90,16 +90,21 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
 
 struct ftrace_ops;
 
+#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
+
 struct ftrace_regs {
 	struct pt_regs		regs;
 };
+#define arch_ftrace_get_regs(fregs) (&(fregs)->regs)
+
+#endif /* CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS */
 
 static __always_inline struct pt_regs *ftrace_get_regs(struct ftrace_regs *fregs)
 {
 	if (!fregs)
 		return NULL;
 
-	return &fregs->regs;
+	return arch_ftrace_get_regs(fregs);
 }
 
 typedef void (*ftrace_func_t)(unsigned long ip, unsigned long parent_ip,
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index a4020c0b4508..6a5b7a818d7d 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -31,6 +31,15 @@ config HAVE_DYNAMIC_FTRACE_WITH_REGS
 config HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 	bool
 
+config HAVE_DYNAMIC_FTRACE_WITH_ARGS
+	bool
+	help
+	 If this is set, then arguments and stack can be found from
+	 the pt_regs passed into the function callback regs parameter
+	 by default, even without setting the REGS flag in the ftrace_ops.
+	 This allows for use of regs_get_kernel_argument() and
+	 kernel_stack_pointer().
+
 config HAVE_FTRACE_MCOUNT_RECORD
 	bool
 	help
-- 
2.28.0

[RFC][PATCH 3/3 v3] livepatching: Use the default ftrace_ops instead of REGS when ARGS is available

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

When CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS is available, the ftrace call
will be able to set the ip of the calling function. This will improve the
performance of live kernel patching where it does not need all the regs to
be stored just to change the instruction pointer.

If all archs that support live kernel patching also support
HAVE_DYNAMIC_FTRACE_WITH_ARGS, then the architecture specific function
klp_arch_set_pc() could be made generic.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 arch/powerpc/include/asm/livepatch.h | 4 +++-
 arch/s390/include/asm/livepatch.h    | 5 ++++-
 arch/x86/include/asm/ftrace.h        | 3 +++
 arch/x86/include/asm/livepatch.h     | 4 ++--
 arch/x86/kernel/ftrace_64.S          | 4 ++++
 include/linux/ftrace.h               | 7 +++++++
 kernel/livepatch/patch.c             | 9 +++++----
 7 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/include/asm/livepatch.h b/arch/powerpc/include/asm/livepatch.h
index 4a3d5d25fed5..ae25e6e72997 100644
--- a/arch/powerpc/include/asm/livepatch.h
+++ b/arch/powerpc/include/asm/livepatch.h
@@ -12,8 +12,10 @@
 #include <linux/sched/task_stack.h>
 
 #ifdef CONFIG_LIVEPATCH
-static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
+static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
 {
+	struct pt_regs *regs = ftrace_get_regs(fregs);
+
 	regs->nip = ip;
 }
 
diff --git a/arch/s390/include/asm/livepatch.h b/arch/s390/include/asm/livepatch.h
index 818612b784cd..d578a8c76676 100644
--- a/arch/s390/include/asm/livepatch.h
+++ b/arch/s390/include/asm/livepatch.h
@@ -11,10 +11,13 @@
 #ifndef ASM_LIVEPATCH_H
 #define ASM_LIVEPATCH_H
 
+#include <linux/ftrace.h>
 #include <asm/ptrace.h>
 
-static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
+static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
 {
+	struct pt_regs *regs = ftrace_get_regs(fregs);
+
 	regs->psw.addr = ip;
 }
 
diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
index 6b175c2468e6..7042e80941e5 100644
--- a/arch/x86/include/asm/ftrace.h
+++ b/arch/x86/include/asm/ftrace.h
@@ -62,6 +62,9 @@ arch_ftrace_get_regs(struct ftrace_regs *fregs)
 		return NULL;
 	return &fregs->regs;
 }
+
+#define ftrace_regs_set_ip(fregs, _ip)		\
+	do { (fregs)->regs.ip = (_ip); } while (0)
 #endif
 
 #endif /*  CONFIG_DYNAMIC_FTRACE */
diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h
index 1fde1ab6559e..59a08d5c6f1d 100644
--- a/arch/x86/include/asm/livepatch.h
+++ b/arch/x86/include/asm/livepatch.h
@@ -12,9 +12,9 @@
 #include <asm/setup.h>
 #include <linux/ftrace.h>
 
-static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
+static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
 {
-	regs->ip = ip;
+	ftrace_regs_set_ip(fregs, ip);
 }
 
 #endif /* _ASM_X86_LIVEPATCH_H */
diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index c4177bd00cd2..d00806dd8eed 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -157,6 +157,10 @@ SYM_INNER_LABEL(ftrace_caller_op_ptr, SYM_L_GLOBAL)
 SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
 	call ftrace_stub
 
+	/* Handlers can change the RIP */
+	movq RIP(%rsp), %rax
+	movq %rax, MCOUNT_REG_SIZE(%rsp)
+
 	restore_mcount_regs
 
 	/*
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 588ea7023a7a..b4eb962e2be9 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -97,6 +97,13 @@ struct ftrace_regs {
 };
 #define arch_ftrace_get_regs(fregs) (&(fregs)->regs)
 
+/*
+ * ftrace_regs_set_ip() is to be defined by the architecture if
+ * to allow setting of the instruction pointer from the ftrace_regs
+ * when HAVE_DYNAMIC_FTRACE_WITH_ARGS is set and it supports
+ * live kernel patching.
+ */
+#define ftrace_regs_set_ip(fregs, ip) do { } while (0)
 #endif /* CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS */
 
 static __always_inline struct pt_regs *ftrace_get_regs(struct ftrace_regs *fregs)
diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
index 9af0a7c8a255..722266472903 100644
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c
@@ -42,7 +42,6 @@ static void notrace klp_ftrace_handler(unsigned long ip,
 				       struct ftrace_ops *fops,
 				       struct ftrace_regs *fregs)
 {
-	struct pt_regs *regs = ftrace_get_regs(fregs);
 	struct klp_ops *ops;
 	struct klp_func *func;
 	int patch_state;
@@ -118,7 +117,7 @@ static void notrace klp_ftrace_handler(unsigned long ip,
 	if (func->nop)
 		goto unlock;
 
-	klp_arch_set_pc(regs, (unsigned long)func->new_func);
+	klp_arch_set_pc(fregs, (unsigned long)func->new_func);
 
 unlock:
 	preempt_enable_notrace();
@@ -200,8 +199,10 @@ static int klp_patch_func(struct klp_func *func)
 			return -ENOMEM;
 
 		ops->fops.func = klp_ftrace_handler;
-		ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS |
-				  FTRACE_OPS_FL_DYNAMIC |
+		ops->fops.flags = FTRACE_OPS_FL_DYNAMIC |
+#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
+				  FTRACE_OPS_FL_SAVE_REGS |
+#endif
 				  FTRACE_OPS_FL_IPMODIFY |
 				  FTRACE_OPS_FL_PERMANENT;
 
-- 
2.28.0

Re: [RFC][PATCH 0/3 v3] ftrace: Add access to function arguments for all callbacks

[Masami Hiramatsu]

On Wed, 28 Oct 2020 20:08:16 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> This is something I wanted to implement a long time ago, but held off until
> there was a good reason to do so. Now it appears that having access to the
> arguments of the function by default is very useful. As a bonus, because
> arguments must be saved regardless before calling a callback, because they
> need to be restored before returning back to the start of the traced
> function, there's not much work to do to have them always be there for
> normal function callbacks.
> 
> The basic idea is that if CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS is set, then
> all callbacks registered to ftrace can use the regs parameter for the stack
> and arguments (kernel_stack_pointer(regs), regs_get_kernel_argument(regs, n)),
> without the need to set REGS that causes overhead by saving all registers as
> REGS simulates a breakpoint.
> 
> This could be extended to move the REGS portion to kprobes itself, and
> remove the SAVE_REGS flag completely, but for now, kprobes still uses the
> full SAVE_REGS support.

Yeah, I would like to keep using the SAVE_REGS support until SAVE_ARGS
implemented on all arch. But in parallel, I will prepare generic
kprobe-on-ftrace handler.

> The last patch extends the WITH_ARGS to allow default function tracing to
> modify the instruction pointer, where livepatching for x86 no longer needs
> to save all registers.
> 
> The idea of this approach is to give enough information to a callback that
> it could retrieve all arguments, which includes the stack pointer and
> instruction pointer.
> 
> This can also be extended to modify the function graph tracer to use the
> function tracer instead of having a separate trampoline.

Anyway, this series (3 patches) looks good to me.

Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>

Thank you!

> 
> Changes since v2:
> 
>  - Change all callback args to use struct ftrace_regs, and if something
>    requires the full regs, it must use the ftrace_get_regs() helper macro,
>    which will return NULL if the regs isn't full (FL_SAVE_REGS set).
>    This addresses a concern by both Peter Zijlsta and Thomas Gleixner that
>    a partially filled pt_regs may be used inappropriately.
> 
>  - No test patch in this version.
> 
>  - Use case using livepatching is added. This passes the test_livepatch.sh
>    selftest.
> 
> Steven Rostedt (VMware) (3):
>       ftrace: Have the callbacks receive a struct ftrace_regs instead of pt_regs
>       ftrace/x86: Allow for arguments to be passed in to ftrace_regs by default
>       livepatching: Use the default ftrace_ops instead of REGS when ARGS is available
> 
> ----
>  arch/powerpc/include/asm/livepatch.h |  4 +++-
>  arch/s390/include/asm/livepatch.h    |  5 ++++-
>  arch/x86/Kconfig                     |  1 +
>  arch/x86/include/asm/ftrace.h        | 18 ++++++++++++++++++
>  arch/x86/include/asm/livepatch.h     |  4 ++--
>  arch/x86/kernel/ftrace_64.S          | 15 +++++++++++++--
>  arch/x86/kernel/kprobes/ftrace.c     |  3 ++-
>  include/linux/ftrace.h               | 28 ++++++++++++++++++++++++++--
>  include/linux/kprobes.h              |  2 +-
>  kernel/livepatch/patch.c             | 10 ++++++----
>  kernel/trace/Kconfig                 |  9 +++++++++
>  kernel/trace/ftrace.c                | 27 +++++++++++++++------------
>  kernel/trace/trace_event_perf.c      |  2 +-
>  kernel/trace/trace_functions.c       |  9 ++++-----
>  kernel/trace/trace_irqsoff.c         |  2 +-
>  kernel/trace/trace_sched_wakeup.c    |  2 +-
>  kernel/trace/trace_selftest.c        | 20 +++++++++++---------
>  kernel/trace/trace_stack.c           |  2 +-
>  18 files changed, 119 insertions(+), 44 deletions(-)


-- 
Masami Hiramatsu <mhiramat@kernel.org>

Re: [RFC][PATCH 3/3 v3] livepatching: Use the default ftrace_ops instead of REGS when ARGS is available

[Miroslav Benes]

(live-patching ML CCed, keeping the complete email for reference)

Hi,

a nit concerning the subject. We use just "livepatch:" as a prefix.

On Wed, 28 Oct 2020, Steven Rostedt wrote:

> From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
> 
> When CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS is available, the ftrace call
> will be able to set the ip of the calling function. This will improve the
> performance of live kernel patching where it does not need all the regs to
> be stored just to change the instruction pointer.
> 
> If all archs that support live kernel patching also support
> HAVE_DYNAMIC_FTRACE_WITH_ARGS, then the architecture specific function
> klp_arch_set_pc() could be made generic.

I think this is a nice idea, which could easily lead to removing 
FTRACE_WITH_REGS altogether. I'm really looking forward to that because 
every consolidation step is welcome.

My only remark is for the config. LIVEPATCH now depends on 
DYNAMIC_FTRACE_WITH_REGS which is not completely true after this change, 
so we should probably make it depend on DYNAMIC_FTRACE_WITH_REGS || 
DYNAMIC_FTRACE_WITH_ARGS, just to reflect the situation better.

Anyway, it passed my tests too and the patch looks good to me, so

Acked-by: Miroslav Benes <mbenes@suse.cz>

M

> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> ---
>  arch/powerpc/include/asm/livepatch.h | 4 +++-
>  arch/s390/include/asm/livepatch.h    | 5 ++++-
>  arch/x86/include/asm/ftrace.h        | 3 +++
>  arch/x86/include/asm/livepatch.h     | 4 ++--
>  arch/x86/kernel/ftrace_64.S          | 4 ++++
>  include/linux/ftrace.h               | 7 +++++++
>  kernel/livepatch/patch.c             | 9 +++++----
>  7 files changed, 28 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/livepatch.h b/arch/powerpc/include/asm/livepatch.h
> index 4a3d5d25fed5..ae25e6e72997 100644
> --- a/arch/powerpc/include/asm/livepatch.h
> +++ b/arch/powerpc/include/asm/livepatch.h
> @@ -12,8 +12,10 @@
>  #include <linux/sched/task_stack.h>
>  
>  #ifdef CONFIG_LIVEPATCH
> -static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
> +static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
>  {
> +	struct pt_regs *regs = ftrace_get_regs(fregs);
> +
>  	regs->nip = ip;
>  }
>  
> diff --git a/arch/s390/include/asm/livepatch.h b/arch/s390/include/asm/livepatch.h
> index 818612b784cd..d578a8c76676 100644
> --- a/arch/s390/include/asm/livepatch.h
> +++ b/arch/s390/include/asm/livepatch.h
> @@ -11,10 +11,13 @@
>  #ifndef ASM_LIVEPATCH_H
>  #define ASM_LIVEPATCH_H
>  
> +#include <linux/ftrace.h>
>  #include <asm/ptrace.h>
>  
> -static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
> +static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
>  {
> +	struct pt_regs *regs = ftrace_get_regs(fregs);
> +
>  	regs->psw.addr = ip;
>  }
>  
> diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
> index 6b175c2468e6..7042e80941e5 100644
> --- a/arch/x86/include/asm/ftrace.h
> +++ b/arch/x86/include/asm/ftrace.h
> @@ -62,6 +62,9 @@ arch_ftrace_get_regs(struct ftrace_regs *fregs)
>  		return NULL;
>  	return &fregs->regs;
>  }
> +
> +#define ftrace_regs_set_ip(fregs, _ip)		\
> +	do { (fregs)->regs.ip = (_ip); } while (0)
>  #endif
>  
>  #endif /*  CONFIG_DYNAMIC_FTRACE */
> diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h
> index 1fde1ab6559e..59a08d5c6f1d 100644
> --- a/arch/x86/include/asm/livepatch.h
> +++ b/arch/x86/include/asm/livepatch.h
> @@ -12,9 +12,9 @@
>  #include <asm/setup.h>
>  #include <linux/ftrace.h>
>  
> -static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
> +static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
>  {
> -	regs->ip = ip;
> +	ftrace_regs_set_ip(fregs, ip);
>  }
>  
>  #endif /* _ASM_X86_LIVEPATCH_H */
> diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
> index c4177bd00cd2..d00806dd8eed 100644
> --- a/arch/x86/kernel/ftrace_64.S
> +++ b/arch/x86/kernel/ftrace_64.S
> @@ -157,6 +157,10 @@ SYM_INNER_LABEL(ftrace_caller_op_ptr, SYM_L_GLOBAL)
>  SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
>  	call ftrace_stub
>  
> +	/* Handlers can change the RIP */
> +	movq RIP(%rsp), %rax
> +	movq %rax, MCOUNT_REG_SIZE(%rsp)
> +
>  	restore_mcount_regs
>  
>  	/*
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 588ea7023a7a..b4eb962e2be9 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -97,6 +97,13 @@ struct ftrace_regs {
>  };
>  #define arch_ftrace_get_regs(fregs) (&(fregs)->regs)
>  
> +/*
> + * ftrace_regs_set_ip() is to be defined by the architecture if
> + * to allow setting of the instruction pointer from the ftrace_regs
> + * when HAVE_DYNAMIC_FTRACE_WITH_ARGS is set and it supports
> + * live kernel patching.
> + */
> +#define ftrace_regs_set_ip(fregs, ip) do { } while (0)
>  #endif /* CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS */
>  
>  static __always_inline struct pt_regs *ftrace_get_regs(struct ftrace_regs *fregs)
> diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
> index 9af0a7c8a255..722266472903 100644
> --- a/kernel/livepatch/patch.c
> +++ b/kernel/livepatch/patch.c
> @@ -42,7 +42,6 @@ static void notrace klp_ftrace_handler(unsigned long ip,
>  				       struct ftrace_ops *fops,
>  				       struct ftrace_regs *fregs)
>  {
> -	struct pt_regs *regs = ftrace_get_regs(fregs);
>  	struct klp_ops *ops;
>  	struct klp_func *func;
>  	int patch_state;
> @@ -118,7 +117,7 @@ static void notrace klp_ftrace_handler(unsigned long ip,
>  	if (func->nop)
>  		goto unlock;
>  
> -	klp_arch_set_pc(regs, (unsigned long)func->new_func);
> +	klp_arch_set_pc(fregs, (unsigned long)func->new_func);
>  
>  unlock:
>  	preempt_enable_notrace();
> @@ -200,8 +199,10 @@ static int klp_patch_func(struct klp_func *func)
>  			return -ENOMEM;
>  
>  		ops->fops.func = klp_ftrace_handler;
> -		ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS |
> -				  FTRACE_OPS_FL_DYNAMIC |
> +		ops->fops.flags = FTRACE_OPS_FL_DYNAMIC |
> +#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
> +				  FTRACE_OPS_FL_SAVE_REGS |
> +#endif
>  				  FTRACE_OPS_FL_IPMODIFY |
>  				  FTRACE_OPS_FL_PERMANENT;
>  
> -- 
> 2.28.0
> 
>