Re: [PATCH] kasan: unpoison use memset to init unaligned object size
From: Andrey Konovalov <andreyknvl@gmail.com>
Date: 2021-06-22 14:04:06
Also in:
linux-arm-kernel, linux-mm, lkml
On Mon, Jun 21, 2021 at 6:45 PM [off-list ref] wrote:
quoted hunk ↗ jump to hunk
From: Yee Lee <redacted> 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 <redacted> --- 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)) return; + if (init && ((unsigned long)size & KASAN_GRANULE_MASK)) { + init = false; + memset((void *)addr, 0, size); + }
With this implementation, we loose the benefit of setting tags and initializing memory with the same instructions. Perhaps a better implementation would be to call hw_set_mem_tag_range() with the size rounded down, and then separately deal with the leftover memory.
size = round_up(size, KASAN_GRANULE_SIZE);
-
hw_set_mem_tag_range((void *)addr, size, tag, init);
}
--
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