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mm/kasan: get rid of speculative shadow checks

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For some unaligned memory accesses we have to check additional byte of
the shadow memory.  Currently we load that byte speculatively to have
only single load + branch on the optimistic fast path.

However, this approach has some downsides:

 - It's unaligned access, so this prevents porting KASAN on
   architectures which doesn't support unaligned accesses.

 - We have to map additional shadow page to prevent crash if speculative
   load happens near the end of the mapped memory. This would
   significantly complicate upcoming memory hotplug support.

I wasn't able to notice any performance degradation with this patch.  So
these speculative loads is just a pain with no gain, let's remove them.

Link: http://lkml.kernel.org/r/20170601162338.23540-1-aryabinin@virtuozzo.com
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Acked-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrey Ryabinin 2017-07-10 15:50:24 -07:00 committed by Linus Torvalds
parent 458f7920f9
commit c634d807d9
1 changed files with 16 additions and 82 deletions
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98
mm/kasan/kasan.c
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@ -134,94 +134,30 @@ static __always_inline bool memory_is_poisoned_1(unsigned long addr)
return false;
}
static __always_inline bool memory_is_poisoned_2(unsigned long addr)
static __always_inline bool memory_is_poisoned_2_4_8(unsigned long addr,
unsigned long size)
{
u16 *shadow_addr = (u16 *)kasan_mem_to_shadow((void *)addr);
u8 *shadow_addr = (u8 *)kasan_mem_to_shadow((void *)addr);
if (unlikely(*shadow_addr)) {
if (memory_is_poisoned_1(addr + 1))
return true;
/*
* Access crosses 8(shadow size)-byte boundary. Such access maps
* into 2 shadow bytes, so we need to check them both.
*/
if (unlikely(((addr + size - 1) & KASAN_SHADOW_MASK) < size - 1))
return *shadow_addr || memory_is_poisoned_1(addr + size - 1);
/*
* 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;
return unlikely(*(u8 *)shadow_addr);
}
return false;
}
static __always_inline bool memory_is_poisoned_4(unsigned long addr)
{
u16 *shadow_addr = (u16 *)kasan_mem_to_shadow((void *)addr);
if (unlikely(*shadow_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;
return unlikely(*(u8 *)shadow_addr);
}
return false;
}
static __always_inline bool memory_is_poisoned_8(unsigned long addr)
{
u16 *shadow_addr = (u16 *)kasan_mem_to_shadow((void *)addr);
if (unlikely(*shadow_addr)) {
if (memory_is_poisoned_1(addr + 7))
return true;
/*
* 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);
}
return false;
return memory_is_poisoned_1(addr + size - 1);
}
static __always_inline bool memory_is_poisoned_16(unsigned long addr)
{
u32 *shadow_addr = (u32 *)kasan_mem_to_shadow((void *)addr);
u16 *shadow_addr = (u16 *)kasan_mem_to_shadow((void *)addr);
if (unlikely(*shadow_addr)) {
u16 shadow_first_bytes = *(u16 *)shadow_addr;
/* Unaligned 16-bytes access maps into 3 shadow bytes. */
if (unlikely(!IS_ALIGNED(addr, KASAN_SHADOW_SCALE_SIZE)))
return *shadow_addr || memory_is_poisoned_1(addr + 15);
if (unlikely(shadow_first_bytes))
return true;
/*
* 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);
}
return false;
return *shadow_addr;
}
static __always_inline unsigned long bytes_is_zero(const u8 *start,
@ -292,11 +228,9 @@ static __always_inline bool memory_is_poisoned(unsigned long addr, size_t size)
case 1:
return memory_is_poisoned_1(addr);
case 2:
return memory_is_poisoned_2(addr);
case 4:
return memory_is_poisoned_4(addr);
case 8:
return memory_is_poisoned_8(addr);
return memory_is_poisoned_2_4_8(addr, size);
case 16:
return memory_is_poisoned_16(addr);
default: