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* [PATCH] kasan: Zero initialize tag in __kasan_kmalloc
@ 2019-05-02 15:35 Nathan Chancellor
  2019-05-02 16:24 ` Andrey Konovalov
  2019-05-02 16:30 ` [PATCH v2] kasan: Initialize tag to 0xff " Nathan Chancellor
  0 siblings, 2 replies; 6+ messages in thread
From: Nathan Chancellor @ 2019-05-02 15:35 UTC (permalink / raw)
  To: Andrey Ryabinin, Alexander Potapenko, Dmitry Vyukov
  Cc: kasan-dev, linux-mm, linux-kernel, Nick Desaulniers,
	clang-built-linux, Nathan Chancellor

When building with -Wuninitialized and CONFIG_KASAN_SW_TAGS unset, Clang
warns:

mm/kasan/common.c:484:40: warning: variable 'tag' is uninitialized when
used here [-Wuninitialized]
        kasan_unpoison_shadow(set_tag(object, tag), size);
                                              ^~~

set_tag ignores tag in this configuration but clang doesn't realize it
at this point in its pipeline, as it points to arch_kasan_set_tag as
being the point where it is used, which will later be expanded to
(void *)(object) without a use of tag. Just zero initialize tag, as it
removes this warning and doesn't change the meaning of the code.

Link: https://github.com/ClangBuiltLinux/linux/issues/465
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
 mm/kasan/common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 36afcf64e016..4c5af68f2a8b 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -464,7 +464,7 @@ static void *__kasan_kmalloc(struct kmem_cache *cache, const void *object,
 {
 	unsigned long redzone_start;
 	unsigned long redzone_end;
-	u8 tag;
+	u8 tag = 0;
 
 	if (gfpflags_allow_blocking(flags))
 		quarantine_reduce();
-- 
2.21.0


^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2019-05-23  8:52 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-05-02 15:35 [PATCH] kasan: Zero initialize tag in __kasan_kmalloc Nathan Chancellor
2019-05-02 16:24 ` Andrey Konovalov
2019-05-02 16:30 ` [PATCH v2] kasan: Initialize tag to 0xff " Nathan Chancellor
2019-05-02 16:40   ` Andrey Konovalov
2019-05-23  1:47     ` Nathan Chancellor
2019-05-23  8:53   ` Andrey Ryabinin

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