From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id 96B5E6B0269 for ; Mon, 1 Aug 2016 11:27:30 -0400 (EDT) Received: by mail-wm0-f69.google.com with SMTP id l4so84673693wml.0 for ; Mon, 01 Aug 2016 08:27:30 -0700 (PDT) Received: from mail-lf0-x233.google.com (mail-lf0-x233.google.com. [2a00:1450:4010:c07::233]) by mx.google.com with ESMTPS id f65si14671888lff.360.2016.08.01.08.27.29 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 01 Aug 2016 08:27:29 -0700 (PDT) Received: by mail-lf0-x233.google.com with SMTP id f93so118233159lfi.2 for ; Mon, 01 Aug 2016 08:27:29 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <579F669A.4090806@virtuozzo.com> References: <1469719879-11761-1-git-send-email-glider@google.com> <1469719879-11761-3-git-send-email-glider@google.com> <579F62D3.8030605@virtuozzo.com> <579F669A.4090806@virtuozzo.com> From: Alexander Potapenko Date: Mon, 1 Aug 2016 17:27:28 +0200 Message-ID: Subject: Re: [PATCH v8 2/3] mm, kasan: align free_meta_offset on sizeof(void*) Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Andrey Ryabinin Cc: Dmitriy Vyukov , Kostya Serebryany , Andrey Konovalov , Christoph Lameter , Andrew Morton , Steven Rostedt , Joonsoo Kim , Joonsoo Kim , Kuthonuzo Luruo , kasan-dev , LKML , Linux Memory Management List On Mon, Aug 1, 2016 at 5:11 PM, Andrey Ryabinin w= rote: > > > On 08/01/2016 05:56 PM, Alexander Potapenko wrote: >> On Mon, Aug 1, 2016 at 4:55 PM, Andrey Ryabinin 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 >>>> --- >>>> 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 =3D *size; >>>> + cache->kasan_info.free_meta_offset =3D >>>> + 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 +=3D 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=3Dlinux-mm&m=3D146971994204507&w=3D2) --=20 Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Stra=C3=9Fe, 33 80636 M=C3=BCnchen Gesch=C3=A4ftsf=C3=BChrer: Matthew Scott Sucherman, Paul Terence Manicle Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org