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Sun, 19 Nov 2023 20:47:31 +0000 Received: from VI1P193MB0752.EURP193.PROD.OUTLOOK.COM ([fe80::fdd2:7dbf:e16c:f4a4]) by VI1P193MB0752.EURP193.PROD.OUTLOOK.COM ([fe80::fdd2:7dbf:e16c:f4a4%4]) with mapi id 15.20.7002.027; Sun, 19 Nov 2023 20:47:31 +0000 From: Juntong Deng To: ryabinin.a.a@gmail.com, glider@google.com, andreyknvl@gmail.com, dvyukov@google.com, vincenzo.frascino@arm.com, akpm@linux-foundation.org Cc: kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kernel-mentees@lists.linuxfoundation.org Subject: [PATCH] kasan: Improve free meta storage in Generic KASAN Date: Mon, 20 Nov 2023 04:46:29 +0800 Message-ID: X-Mailer: git-send-email 2.39.2 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-TMN: [SDLZg+o5aRh8rljxMKf9GYjanOwFCPPo] X-ClientProxiedBy: LO4P123CA0068.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:153::19) To VI1P193MB0752.EURP193.PROD.OUTLOOK.COM (2603:10a6:800:32::19) X-Microsoft-Original-Message-ID: <20231119204629.50560-1-juntong.deng@outlook.com> MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VI1P193MB0752:EE_|DB9P193MB1354:EE_ X-MS-Office365-Filtering-Correlation-Id: 3cb3973d-d264-4571-b623-08dbe940c005 X-Microsoft-Antispam: BCL:0; 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After the improvement, even when the object is smaller than free meta, it is still possible to store part of the free meta in the object, reducing the increased size of the redzone. Example: free meta size: 16 bytes alloc meta size: 16 bytes object size: 8 bytes optimal redzone size (object_size <= 64): 16 bytes Before improvement: actual redzone size = alloc meta size + free meta size = 32 bytes After improvement: actual redzone size = alloc meta size + (free meta size - object size) = 24 bytes Suggested-by: Dmitry Vyukov Signed-off-by: Juntong Deng --- mm/kasan/generic.c | 30 ++++++++++++++++++++---------- 1 file changed, 20 insertions(+), 10 deletions(-) diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c index 4d837ab83f08..286b80661a80 100644 --- a/mm/kasan/generic.c +++ b/mm/kasan/generic.c @@ -361,6 +361,8 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size, { unsigned int ok_size; unsigned int optimal_size; + unsigned int rem_free_meta_size; + unsigned int orig_alloc_meta_offset; if (!kasan_requires_meta()) return; @@ -394,6 +396,9 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size, /* Continue, since free meta might still fit. */ } + ok_size = *size; + orig_alloc_meta_offset = cache->kasan_info.alloc_meta_offset; + /* * Add free meta into redzone when it's not possible to store * it in the object. This is the case when: @@ -401,21 +406,26 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size, * be touched after it was freed, or * 2. Object has a constructor, which means it's expected to * retain its content until the next allocation, or - * 3. Object is too small. * Otherwise cache->kasan_info.free_meta_offset = 0 is implied. + * Even if the object is smaller than free meta, it is still + * possible to store part of the free meta in the object. */ - if ((cache->flags & SLAB_TYPESAFE_BY_RCU) || cache->ctor || - cache->object_size < sizeof(struct kasan_free_meta)) { - ok_size = *size; - + if ((cache->flags & SLAB_TYPESAFE_BY_RCU) || cache->ctor) { cache->kasan_info.free_meta_offset = *size; *size += sizeof(struct kasan_free_meta); + } else if (cache->object_size < sizeof(struct kasan_free_meta)) { + rem_free_meta_size = sizeof(struct kasan_free_meta) - + cache->object_size; + *size += rem_free_meta_size; + if (cache->kasan_info.alloc_meta_offset != 0) + cache->kasan_info.alloc_meta_offset += rem_free_meta_size; + } - /* If free meta doesn't fit, don't add it. */ - if (*size > KMALLOC_MAX_SIZE) { - cache->kasan_info.free_meta_offset = KASAN_NO_FREE_META; - *size = ok_size; - } + /* If free meta doesn't fit, don't add it. */ + if (*size > KMALLOC_MAX_SIZE) { + cache->kasan_info.free_meta_offset = KASAN_NO_FREE_META; + cache->kasan_info.alloc_meta_offset = orig_alloc_meta_offset; + *size = ok_size; } /* Calculate size with optimal redzone. */ -- 2.39.2