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.  Also add some comments in shadow
check functions.

Signed-off-by: Xishi Qiu <qiuxishi@huawei.com>
Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andrey Konovalov <adech.fo@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 22 insertions, 2 deletions

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 2b21ccd55cd4..d41b21bce6a0 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);