From: Nathan Chancellor natechancellor@gmail.com Subject: kasan: initialize tag to 0xff in __kasan_kmalloc

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. 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 Link: http://lkml.kernel.org/r/20190502163057.6603-1-natechancellor@gmail.com Fixes: 7f94ffbc4c6a ("kasan: add hooks implementation for tag-based mode") Signed-off-by: Nathan Chancellor natechancellor@gmail.com Reviewed-by: Andrey Konovalov andreyknvl@google.com Reviewed-by: Andrey Ryabinin aryabinin@virtuozzo.com Cc: Alexander Potapenko glider@google.com Cc: Dmitry Vyukov dvyukov@google.com Cc: Nick Desaulniers ndesaulniers@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/kasan/common.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/kasan/common.c~kasan-initialize-tag-to-0xff-in-__kasan_kmalloc +++ a/mm/kasan/common.c @@ -464,7 +464,7 @@ static void *__kasan_kmalloc(struct kmem { unsigned long redzone_start; unsigned long redzone_end; - u8 tag; + u8 tag = 0xff;

if (gfpflags_allow_blocking(flags)) quarantine_reduce(); _