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From:   Mark Rutland <mark.rutland@arm.com>
To:     linux-kernel@vger.kernel.org
Cc:     mark.rutland@arm.com, mhiramat@kernel.org, rostedt@goodmis.org
Subject: [PATCH] tracepoint: Fix CFI failures with tp_stub_func
Date:   Thu, 23 Mar 2023 11:40:12 +0000
Message-Id: <20230323114012.2162285-1-mark.rutland@arm.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

When CLANG_CFI is in use, using tracing will occasionally result in
CFI failures, e.g.

| CFI failure at syscall_trace_enter+0x66c/0x7d0 (target: tp_stub_func+0x0/0x2c; expected type: 0x4877830c)
| Internal error: Oops - CFI: 00000000f200823a [#1] PREEMPT SMP
| CPU: 2 PID: 118 Comm: klogd Not tainted 6.3.0-rc3-00002-gc242ea6f2f98 #2
| Hardware name: linux,dummy-virt (DT)
| pstate: 30400005 (nzCV daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
| pc : syscall_trace_enter+0x66c/0x7d0
| lr : syscall_trace_enter+0x5e8/0x7d0
| sp : ffff800015ce7d80
| x29: ffff800015ce7d80 x28: ffff000017538000 x27: 0000000000000003
| x26: ffff8000084c9454 x25: ffff00001182bd10 x24: dfff800000000000
| x23: 1fffe00002ea7001 x22: ffff00001182bd10 x21: ffff000017538008
| x20: ffff000017538000 x19: ffff800015ce7eb0 x18: 0000000000000000
| x17: 000000004877830c x16: 00000000a540670c x15: 0000000000000000
| x14: 0000000000000000 x13: 0000000000000000 x12: ff80800008039d8c
| x11: ff80800008039dd0 x10: 0000000000000000 x9 : 0000000000000000
| x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000
| x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000
| x2 : 00000000000000ce x1 : ffff800015ce7eb0 x0 : ffff800013d55000
| Call trace:
|  syscall_trace_enter+0x66c/0x7d0
|  el0_svc_common+0x1dc/0x268
|  do_el0_svc+0x70/0x1a4
|  el0_svc+0x58/0x14c
|  el0t_64_sync_handler+0x84/0xf0
|  el0t_64_sync+0x190/0x194
| Code: 72906191 72a90ef1 6b11021f 54000040 (d4304740)
| ---[ end trace 0000000000000000 ]---

This happens because the function prototype of tp_sub_func doesn't match
the prototype of the tracepoint function. As each tracepoint may have a
distinct prototype, it's not possible to share a common stub function.

Avoid this by creating a stub function for each tracepoint with the
correct prototype, and using these rather than tp_stub_func.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org
---
 include/linux/tracepoint-defs.h |  1 +
 include/linux/tracepoint.h      |  5 +++++
 kernel/tracepoint.c             | 31 ++++++++++++++-----------------
 3 files changed, 20 insertions(+), 17 deletions(-)

diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h
index e7c2276be33eb..a306ac7255220 100644
--- a/include/linux/tracepoint-defs.h
+++ b/include/linux/tracepoint-defs.h
@@ -35,6 +35,7 @@ struct tracepoint {
 	struct static_call_key *static_call_key;
 	void *static_call_tramp;
 	void *iterator;
+	void *stub;
 	int (*regfunc)(void);
 	void (*unregfunc)(void);
 	struct tracepoint_func __rcu *funcs;
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 6811e43c1b5c2..1640926441910 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -303,6 +303,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 	__section("__tracepoints_strings") = #_name;			\
 	extern struct static_call_key STATIC_CALL_KEY(tp_func_##_name);	\
 	int __traceiter_##_name(void *__data, proto);			\
+	void __tracestub_##_name(void *, proto);			\
 	struct tracepoint __tracepoint_##_name	__used			\
 	__section("__tracepoints") = {					\
 		.name = __tpstrtab_##_name,				\
@@ -310,6 +311,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 		.static_call_key = &STATIC_CALL_KEY(tp_func_##_name),	\
 		.static_call_tramp = STATIC_CALL_TRAMP_ADDR(tp_func_##_name), \
 		.iterator = &__traceiter_##_name,			\
+		.stub = &__tracestub_##_name,				\
 		.regfunc = _reg,					\
 		.unregfunc = _unreg,					\
 		.funcs = NULL };					\
@@ -330,6 +332,9 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 		}							\
 		return 0;						\
 	}								\
+	void __tracestub_##_name(void *__data, proto)			\
+	{								\
+	}								\
 	DEFINE_STATIC_CALL(tp_func_##_name, __traceiter_##_name);
 
 #define DEFINE_TRACE(name, proto, args)		\
diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 8d1507dd07246..d9186629a0095 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -98,12 +98,6 @@ struct tp_probes {
 	struct tracepoint_func probes[];
 };
 
-/* Called in removal of a func but failed to allocate a new tp_funcs */
-static void tp_stub_func(void)
-{
-	return;
-}
-
 static inline void *allocate_probes(int count)
 {
 	struct tp_probes *p  = kmalloc(struct_size(p, probes, count),
@@ -177,13 +171,15 @@ static void debug_print_probes(struct tracepoint_func *funcs)
 }
 
 static struct tracepoint_func *
-func_add(struct tracepoint_func **funcs, struct tracepoint_func *tp_func,
+func_add(struct tracepoint *tp, struct tracepoint_func **funcs,
+	 struct tracepoint_func *tp_func,
 	 int prio)
 {
 	struct tracepoint_func *old, *new;
 	int iter_probes;	/* Iterate over old probe array. */
 	int nr_probes = 0;	/* Counter for probes */
 	int pos = -1;		/* Insertion position into new array */
+	void *stub_func = tp->stub;
 
 	if (WARN_ON(!tp_func->func))
 		return ERR_PTR(-EINVAL);
@@ -193,7 +189,7 @@ func_add(struct tracepoint_func **funcs, struct tracepoint_func *tp_func,
 	if (old) {
 		/* (N -> N+1), (N != 0, 1) probes */
 		for (iter_probes = 0; old[iter_probes].func; iter_probes++) {
-			if (old[iter_probes].func == tp_stub_func)
+			if (old[iter_probes].func == stub_func)
 				continue;	/* Skip stub functions. */
 			if (old[iter_probes].func == tp_func->func &&
 			    old[iter_probes].data == tp_func->data)
@@ -208,7 +204,7 @@ func_add(struct tracepoint_func **funcs, struct tracepoint_func *tp_func,
 	if (old) {
 		nr_probes = 0;
 		for (iter_probes = 0; old[iter_probes].func; iter_probes++) {
-			if (old[iter_probes].func == tp_stub_func)
+			if (old[iter_probes].func == stub_func)
 				continue;
 			/* Insert before probes of lower priority */
 			if (pos < 0 && old[iter_probes].prio < prio)
@@ -229,11 +225,12 @@ func_add(struct tracepoint_func **funcs, struct tracepoint_func *tp_func,
 	return old;
 }
 
-static void *func_remove(struct tracepoint_func **funcs,
-		struct tracepoint_func *tp_func)
+static void *func_remove(struct tracepoint *tp, struct tracepoint_func **funcs,
+			 struct tracepoint_func *tp_func)
 {
 	int nr_probes = 0, nr_del = 0, i;
 	struct tracepoint_func *old, *new;
+	void *stub_func = tp->stub;
 
 	old = *funcs;
 
@@ -246,7 +243,7 @@ static void *func_remove(struct tracepoint_func **funcs,
 		for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
 			if ((old[nr_probes].func == tp_func->func &&
 			     old[nr_probes].data == tp_func->data) ||
-			    old[nr_probes].func == tp_stub_func)
+			    old[nr_probes].func == stub_func)
 				nr_del++;
 		}
 	}
@@ -269,7 +266,7 @@ static void *func_remove(struct tracepoint_func **funcs,
 			for (i = 0; old[i].func; i++) {
 				if ((old[i].func != tp_func->func ||
 				     old[i].data != tp_func->data) &&
-				    old[i].func != tp_stub_func)
+				    old[i].func != stub_func)
 					new[j++] = old[i];
 			}
 			new[nr_probes - nr_del].func = NULL;
@@ -277,12 +274,12 @@ static void *func_remove(struct tracepoint_func **funcs,
 		} else {
 			/*
 			 * Failed to allocate, replace the old function
-			 * with calls to tp_stub_func.
+			 * with calls to stub_func.
 			 */
 			for (i = 0; old[i].func; i++) {
 				if (old[i].func == tp_func->func &&
 				    old[i].data == tp_func->data)
-					WRITE_ONCE(old[i].func, tp_stub_func);
+					WRITE_ONCE(old[i].func, stub_func);
 			}
 			*funcs = old;
 		}
@@ -335,7 +332,7 @@ static int tracepoint_add_func(struct tracepoint *tp,
 
 	tp_funcs = rcu_dereference_protected(tp->funcs,
 			lockdep_is_held(&tracepoints_mutex));
-	old = func_add(&tp_funcs, func, prio);
+	old = func_add(tp, &tp_funcs, func, prio);
 	if (IS_ERR(old)) {
 		WARN_ON_ONCE(warn && PTR_ERR(old) != -ENOMEM);
 		return PTR_ERR(old);
@@ -400,7 +397,7 @@ static int tracepoint_remove_func(struct tracepoint *tp,
 
 	tp_funcs = rcu_dereference_protected(tp->funcs,
 			lockdep_is_held(&tracepoints_mutex));
-	old = func_remove(&tp_funcs, func);
+	old = func_remove(tp, &tp_funcs, func);
 	if (WARN_ON_ONCE(IS_ERR(old)))
 		return PTR_ERR(old);
 
-- 
2.30.2