[PATCH V3] kasan: use IS_ALIGNED in memory_is_poisoned_8()

[Xishi Qiu]

Use IS_ALIGNED() to determine whether the shadow span two bytes. It
generates less code and more readable. Also 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@xxxxxxxxxx>
---
 mm/kasan/kasan.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 8da2114..d0a3af8 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -86,6 +86,11 @@ static __always_inline bool memory_is_poisoned_2(unsigned long addr)
 		if (memory_is_poisoned_1(addr + 1))
 			return true;
 
+		/*
+		 * If single shadow byte covers 2-byte access, we don't
+		 * need to do anything more. Otherwise, test the first
+		 * shadow byte.
+		 */
 		if (likely(((addr + 1) & KASAN_SHADOW_MASK) != 0))
 			return false;
 
@@ -103,6 +108,11 @@ static __always_inline bool memory_is_poisoned_4(unsigned long addr)
 		if (memory_is_poisoned_1(addr + 3))
 			return true;
 
+		/*
+		 * If single shadow byte covers 4-byte access, we don't
+		 * need to do anything more. Otherwise, test the first
+		 * shadow byte.
+		 */
 		if (likely(((addr + 3) & KASAN_SHADOW_MASK) >= 3))
 			return false;
 
@@ -120,7 +130,12 @@ 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 single shadow byte covers 8-byte access, we don't
+		 * need to do anything more. Otherwise, test the first
+		 * shadow byte.
+		 */
+		if (likely(IS_ALIGNED(addr, KASAN_SHADOW_SCALE_SIZE)))
 			return false;
 
 		return unlikely(*(u8 *)shadow_addr);
@@ -139,7 +154,12 @@ 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 two shadow bytes covers 16-byte access, we don't
+		 * need to do anything more. Otherwise, test the last
+		 * shadow byte.
+		 */
+		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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