[PATCH v5 05/15] tracepoint: Exclude tp_stub_func from CFI checking

[Sami Tolvanen]

If allocate_probes fails, func_remove replaces the old function
with a pointer to tp_stub_func, which is called using a mismatching
function pointer that will always trip indirect call checks with
CONFIG_CFI_CLANG. Use DEFINE_CFI_IMMEDATE_RETURN_STUB to define
tp_stub_func to allow it to pass CFI checking.

Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx>
---
 kernel/tracepoint.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 64ea283f2f86..8a0d463c8507 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -9,6 +9,7 @@
 #include <linux/list.h>
 #include <linux/rcupdate.h>
 #include <linux/tracepoint.h>
+#include <linux/cfi.h>
 #include <linux/err.h>
 #include <linux/slab.h>
 #include <linux/sched/signal.h>
@@ -99,10 +100,7 @@ struct tp_probes {
 };
 
 /* Called in removal of a func but failed to allocate a new tp_funcs */
-static void tp_stub_func(void)
-{
-	return;
-}
+static DEFINE_CFI_IMMEDIATE_RETURN_STUB(tp_stub_func);
 
 static inline void *allocate_probes(int count)
 {
-- 
2.33.0.1079.g6e70778dc9-goog