linux-hardening - [PATCH v5 05/15] tracepoint: Exclude tp_stub

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Date:   Wed, 13 Oct 2021 11:16:48 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     x86@...nel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH v5 05/15] tracepoint: Exclude tp_stub_func from CFI checking

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@...gle.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>
Tested-by: Sedat Dilek <sedat.dilek@...il.com>
---
 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