Hi,
Thanks for taking a look at this patchstack. I apologize for the delay
in responding.
On 07/10/2017 01:44 AM, Dmitry Vyukov wrote:
+
+ const void *left_redzone = (const void *)(addr -
+ KASAN_ALLOCA_REDZONE_SIZE);
+ const void *right_redzone = (const void *)(addr + rounded_up_size);
Please check that size is rounded to KASAN_ALLOCA_REDZONE_SIZE. That's
the expectation, right? That can change is clang silently.
+ kasan_poison_shadow(left_redzone, KASAN_ALLOCA_REDZONE_SIZE,
+ KASAN_ALLOCA_LEFT);
+ kasan_poison_shadow(right_redzone,
+ padding_size + KASAN_ALLOCA_REDZONE_SIZE,
+ KASAN_ALLOCA_RIGHT);
We also need to poison the unaligned part at the end of the object
from size to rounded_up_size. You can see how we do it for heap
objects.
The expectation is that `size' is the exact size of the alloca()ed
object. `rounded_up_size' then adds the 0-7 bytes needed to adjust the
size to the ASAN shadow scale. So `addr + rounded_up_size' should be
the correct place to start poisoning.
In retrospect this part of the code was pretty confusing. How about
this? I think its intent is clearer, plus it's a closer match for the
description in my commit message:
unsigned long left_redzone_start;
unsigned long object_end;
unsigned long right_redzone_start, right_redzone_end;
left_redzone_start = addr - KASAN_ALLOCA_REDZONE_SIZE;
kasan_poison_shadow((const void *)left_redzone_start,
KASAN_ALLOCA_REDZONE_SIZE,
KASAN_ALLOCA_LEFT);
object_end = round_up(addr + size, KASAN_SHADOW_SCALE_SIZE);
right_redzone_start = round_up(object_end, KASAN_ALLOCA_REDZONE_SIZE);
right_redzone_end = right_redzone_start + KASAN_ALLOCA_REDZONE_SIZE;
kasan_poison_shadow((const void *)object_end,
right_redzone_end - object_end,
KASAN_ALLOCA_RIGHT);
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