The patch titled Subject: kasan: improve free meta storage in Generic KASAN has been added to the -mm mm-unstable branch. Its filename is kasan-improve-free-meta-storage-in-generic-kasan.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kasan-improve-free-meta-storage-in-generic-kasan.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Juntong Deng <juntong.deng@xxxxxxxxxxx> Subject: kasan: improve free meta storage in Generic KASAN Date: Mon, 20 Nov 2023 04:46:29 +0800 Currently free meta can only be stored in object if the object is not smaller than free meta. 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 Link: https://lkml.kernel.org/r/VI1P193MB0752DE2CCD9046B5FED0AA8E99B5A@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Juntong Deng <juntong.deng@xxxxxxxxxxx> Suggested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx> Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/kasan/generic.c | 30 ++++++++++++++++++++---------- 1 file changed, 20 insertions(+), 10 deletions(-) --- a/mm/kasan/generic.c~kasan-improve-free-meta-storage-in-generic-kasan +++ a/mm/kasan/generic.c @@ -362,6 +362,8 @@ void kasan_cache_create(struct kmem_cach { 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; @@ -395,6 +397,9 @@ void kasan_cache_create(struct kmem_cach /* 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: @@ -402,21 +407,26 @@ void kasan_cache_create(struct kmem_cach * 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. */ _ Patches currently in -mm which might be from juntong.deng@xxxxxxxxxxx are kasan-improve-free-meta-storage-in-generic-kasan.patch