[PATCH V2] kasan: use IS_ALIGNED in memory_is_poisoned_8()

[Xishi Qiu <qiuxishi@huawei.com>]

Use IS_ALIGNED() to determine whether the shadow span two bytes.
It generates less code and more readable. Add some comments in 
shadow check functions.

Please apply "kasan: fix last shadow judgement in memory_is_poisoned_16()"
first.

Signed-off-by: Xishi Qiu <qiuxishi@huawei.com>
---
 mm/kasan/kasan.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 8da2114..00d5605 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -86,6 +86,10 @@ static __always_inline bool memory_is_poisoned_2(unsigned long addr)
 		if (memory_is_poisoned_1(addr + 1))
 			return true;
 
+		/*
+		 * If the shadow spans two bytes, the first byte should
+		 * be zero.
+		 */
 		if (likely(((addr + 1) & KASAN_SHADOW_MASK) != 0))
 			return false;
 
@@ -103,6 +107,10 @@ static __always_inline bool memory_is_poisoned_4(unsigned long addr)
 		if (memory_is_poisoned_1(addr + 3))
 			return true;
 
+		/*
+		 * If the shadow spans two bytes, the first byte should
+		 * be zero.
+		 */
 		if (likely(((addr + 3) & KASAN_SHADOW_MASK) >= 3))
 			return false;
 
@@ -120,7 +128,11 @@ static __always_inline bool memory_is_poisoned_8(unsigned long addr)
 		if (memory_is_poisoned_1(addr + 7))
 			return true;
 
-		if (likely(((addr + 7) & KASAN_SHADOW_MASK) >= 7))
+		/*
+		 * If the shadow spans two bytes, the first byte should
+		 * be zero.
+		 */
+		if (likely(IS_ALIGNED(addr, KASAN_SHADOW_SCALE_SIZE)))
 			return false;
 
 		return unlikely(*(u8 *)shadow_addr);
@@ -139,7 +151,12 @@ static __always_inline bool memory_is_poisoned_16(unsigned long addr)
 		if (unlikely(shadow_first_bytes))
 			return true;
 
-		if (likely(IS_ALIGNED(addr, 8)))
+		/*
+		 * If the shadow spans three bytes, we should continue to
+		 * check the last byte. The first two bytes which we
+		 * checked above should always be zero.
+		 */
+		if (likely(IS_ALIGNED(addr, KASAN_SHADOW_SCALE_SIZE)))
 			return false;
 
 		return memory_is_poisoned_1(addr + 15);
-- 
2.0.0


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