[Devel] [PATCH vz10 2/2] tracing: Fix CFI violation in probestub being called by tprobes

[Eva Kurchatova]

The probestub is a function to allow tprobes to hook to a tracepoint to
gain access to its parameters. The function itself is only referenced by
the tracepoint structure which lives in the __tracepoint section. objtool
explicitly ignores that section and when processing functions in the
kernel, if it detects one that has no references it will seal it to have
its ENDBR stripped on boot up.

This means when a tprobe is attached to the sched_wakeup tracepoint, when it
is triggered it will call __probestub_sched_wakeup and due to the missing
ENDBR on a CFI-enabled machine it will take a #CP exception.

Fix this by adding CFI_NOSEAL annotation to probestub declaration.

Cc: stable at vger.kernel.org
Acked-by: Masami Hiramatsu (Google) <mhiramat at kernel.org>
Link: https://patch.msgid.link/20260603153147.573589-1-eva.kurchatova@virtuozzo.com
Fixes: d5173f753750 ("objtool: Exclude __tracepoints data from ENDBR checks")
Signed-off-by: Eva Kurchatova <eva.kurchatova at virtuozzo.com>
[ Updated change log ]
Signed-off-by: Steven Rostedt <rostedt at goodmis.org>

(cherry picked from commit 0652a3daa78723f955b1ebeb621665ce72bec53e)
Signed-off-by: Eva Kurchatova <eva.kurchatova at virtuozzo.com>

https://virtuozzo.atlassian.net/browse/VSTOR-131560
Feature: fix tracepoint
---
 include/linux/tracepoint.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 583d962abcc3..2ba023625a6f 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -19,6 +19,7 @@
 #include <linux/rcupdate.h>
 #include <linux/tracepoint-defs.h>
 #include <linux/static_call.h>
+#include <linux/cfi.h>
 
 struct module;
 struct tracepoint;
@@ -356,6 +357,13 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 	void __probestub_##_name(void *__data, proto)			\
 	{								\
 	}								\
+	/*								\
+	 * Annotate the probestub 'CFI_NOSEAL' to stop objtool from	\
+	 * requesting the kernel remove the ENDBR, because the only	\
+	 * references to the function are in the __tracepoint section,	\
+	 * that objtool doesn't scan.					\
+	 */								\
+	CFI_NOSEAL(__probestub_##_name);				\
 	DEFINE_STATIC_CALL(tp_func_##_name, __traceiter_##_name);
 
 #define DEFINE_TRACE_FN(_name, _reg, _unreg, _proto, _args)		\
-- 
2.54.0