[PATCH v2] kasan: Initialize tag to 0xff in __kasan_kmalloc

From: Nathan Chancellor
Date: Thu May 02 2019 - 12:32:05 EST

When building with -Wuninitialized and CONFIG_KASAN_SW_TAGS unset, Clang

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. Initialize tag to 0xff, 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@xxxxxxxxx>

v1 -> v2:

* Initialize tag to 0xff at Andrey's request

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..242fdc01aaa9 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 = 0xff;

if (gfpflags_allow_blocking(flags))