Messages in this thread | | | From | Alexander Potapenko <> | Date | Mon, 1 Aug 2016 17:27:28 +0200 | Subject | Re: [PATCH v8 2/3] mm, kasan: align free_meta_offset on sizeof(void*) |
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On Mon, Aug 1, 2016 at 5:11 PM, Andrey Ryabinin <aryabinin@virtuozzo.com> wrote: > > > On 08/01/2016 05:56 PM, Alexander Potapenko wrote: >> On Mon, Aug 1, 2016 at 4:55 PM, Andrey Ryabinin <aryabinin@virtuozzo.com> wrote: >>> >>> >>> On 07/28/2016 06:31 PM, Alexander Potapenko wrote: >>>> When free_meta_offset is not zero, it is usually aligned on 4 bytes, >>>> because the size of preceding kasan_alloc_meta is aligned on 4 bytes. >>>> As a result, accesses to kasan_free_meta fields may be misaligned. >>>> >>>> Signed-off-by: Alexander Potapenko <glider@google.com> >>>> --- >>>> mm/kasan/kasan.c | 3 ++- >>>> 1 file changed, 2 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c >>>> index 6845f92..0379551 100644 >>>> --- a/mm/kasan/kasan.c >>>> +++ b/mm/kasan/kasan.c >>>> @@ -390,7 +390,8 @@ void kasan_cache_create(struct kmem_cache *cache, size_t *size, >>>> /* Add free meta. */ >>>> if (cache->flags & SLAB_DESTROY_BY_RCU || cache->ctor || >>>> cache->object_size < sizeof(struct kasan_free_meta)) { >>>> - cache->kasan_info.free_meta_offset = *size; >>>> + cache->kasan_info.free_meta_offset = >>>> + ALIGN(*size, sizeof(void *)); >>> >>> This cannot work. >> Well, it does, at least on my tests. > > JFYI. You aligned only meta offset, but didn't change the size, so after the '*size += sizeof(struct kasan_free_meta);' > *size may point into the middle of free_meta struct. > Plus, alignment wasn't taken into account in kasan_metadata_size(). That's what I do in PATCH 3/3 (https://marc.info/?l=linux-mm&m=146971994204507&w=2)
-- Alexander Potapenko Software Engineer
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