[PATCH] kasan: unpoison use memset to init unaligned object size

yee.lee at mediatek.com yee.lee at mediatek.com
Mon Jun 21 08:44:41 PDT 2021

From: Yee Lee <yee.lee at mediatek.com>

This patch adds a memset to initialize object of unaligned size.
Duing to the MTE granulrity, the integrated initialization using
hwtag instruction will force clearing out bytes in granular size,
which may cause undesired effect, such as overwriting to the redzone
of SLUB debug. In this patch, for the unaligned object size, function
uses memset to initailize context instead of the hwtag instruction.

Signed-off-by: Yee Lee <yee.lee at mediatek.com>
 mm/kasan/kasan.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 8f450bc28045..d8faa64614b7 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -387,8 +387,11 @@ static inline void kasan_unpoison(const void *addr, size_t size, bool init)
 	if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK))
+	if (init && ((unsigned long)size & KASAN_GRANULE_MASK)) {
+		init = false;
+		memset((void *)addr, 0, size);
+	}
 	size = round_up(size, KASAN_GRANULE_SIZE);
 	hw_set_mem_tag_range((void *)addr, size, tag, init);

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