[PATCH] kasan: [v2]unpoison use memzero to init unaligned object

[yee.lee at mediatek.com]

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

Follows the discussion: https://patchwork.kernel.org/project/linux-mediatek/list/?series=504439

This patch Add memzero_explict to initialize unaligned object.

Based on the integrateion of initialization in kasan_unpoison(). The hwtag instructions, constrained with its granularity, has to overwrite the data btyes in unaligned objects. This would cause issue when it works with SLUB debug redzoning.

In this patch, an additional initalizaing path is added for the unaligned objects. It contains memzero_explict() to clear out the data and disables its init flag for the following hwtag actions.

In lab test, this path is executed about 1.1%(941/80854) within the overall kasan_unpoison during a non-debug booting process.

Lab test: QEMU5.2 (+mte) / linux kernel 5.13-rc7

Signed-off-by: Yee Lee <yee.lee at mediatek.com>
---
 mm/kasan/kasan.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index d8faa64614b7..edc11bcc3ff3 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -389,7 +389,7 @@ static inline void kasan_unpoison(const void *addr, size_t size, bool init)
 		return;
 	if (init && ((unsigned long)size & KASAN_GRANULE_MASK)) {
 		init = false;
-		memset((void *)addr, 0, size);
+		memzero_explicit((void *)addr, size);
 	}
 	size = round_up(size, KASAN_GRANULE_SIZE);
 	hw_set_mem_tag_range((void *)addr, size, tag, init);
2.18.0