linux-kernel - [PATCH] kasan: fix last shadow judgement in memory_is_poisoned

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Date:	Tue, 8 Sep 2015 09:42:27 +0800
From:	Xishi Qiu <qiuxishi@...wei.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>, <adech.fo@...il.com>,
	<rusty@...tcorp.com.au>, <mmarek@...e.cz>
CC:	Linux MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	<zhongjiang@...wei.com>
Subject: [PATCH] kasan: fix last shadow judgement in memory_is_poisoned_16()

The shadow which correspond 16 bytes may span 2 or 3 bytes. If shadow
only take 2 bytes, we can return in "if (likely(!last_byte)) ...", but
it calculates wrong, so fix it.

Signed-off-by: Xishi Qiu <qiuxishi@...wei.com>
---
 mm/kasan/kasan.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 7b28e9c..8da2114 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -135,12 +135,11 @@ static __always_inline bool memory_is_poisoned_16(unsigned long addr)
 
 	if (unlikely(*shadow_addr)) {
 		u16 shadow_first_bytes = *(u16 *)shadow_addr;
-		s8 last_byte = (addr + 15) & KASAN_SHADOW_MASK;
 
 		if (unlikely(shadow_first_bytes))
 			return true;
 
-		if (likely(!last_byte))
+		if (likely(IS_ALIGNED(addr, 8)))
 			return false;
 
 		return memory_is_poisoned_1(addr + 15);
-- 
1.7.1


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