linux-hardening - [PATCH v3 05/16] tracepoint: Exclude tp_stub

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Date:   Tue, 14 Sep 2021 12:10:34 -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>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH v3 05/16] 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's 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>
---
 kernel/tracepoint.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 64ea283f2f86..58acc7d86c3f 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -99,10 +99,7 @@ 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)
 {
-- 
2.33.0.309.g3052b89438-goog