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