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Message-ID: <CA+fCnZfJqH=dNsD+aNoGbf-LJ_qn=2fbr-U0nj8wi4u2+V3iEw@mail.gmail.com>
Date: Thu, 27 Oct 2022 21:27:11 +0200
From: Andrey Konovalov <andreyknvl@...il.com>
To: Feng Tang <feng.tang@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Vlastimil Babka <vbabka@...e.cz>,
Christoph Lameter <cl@...ux.com>,
Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Roman Gushchin <roman.gushchin@...ux.dev>,
Hyeonggon Yoo <42.hyeyoo@...il.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Kees Cook <keescook@...omium.org>,
Dave Hansen <dave.hansen@...el.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
kernel test robot <oliver.sang@...el.com>,
Andrey Ryabinin <ryabinin.a.a@...il.com>,
Alexander Potapenko <glider@...gle.com>,
Vincenzo Frascino <vincenzo.frascino@....com>
Subject: Re: [PATCH v7 2/3] mm: kasan: Extend kasan_metadata_size() to also
cover in-object size
On Fri, Oct 21, 2022 at 5:24 AM Feng Tang <feng.tang@...el.com> wrote:
>
> When kasan is enabled for slab/slub, it may save kasan' free_meta
> data in the former part of slab object data area in slab object's
> free path, which works fine.
>
> There is ongoing effort to extend slub's debug function which will
> redzone the latter part of kmalloc object area, and when both of
> the debug are enabled, there is possible conflict, especially when
> the kmalloc object has small size, as caught by 0Day bot [1].
>
> To solve it, slub code needs to know the in-object kasan's meta
> data size. Currently, there is existing kasan_metadata_size()
> which returns the kasan's metadata size inside slub's metadata
> area, so extend it to also cover the in-object meta size by
> adding a boolean flag 'in_object'.
>
> There is no functional change to existing code logic.
>
> [1]. https://lore.kernel.org/lkml/YuYm3dWwpZwH58Hu@xsang-OptiPlex-9020/
> Reported-by: kernel test robot <oliver.sang@...el.com>
> Suggested-by: Andrey Konovalov <andreyknvl@...il.com>
> Signed-off-by: Feng Tang <feng.tang@...el.com>
> Reviewed-by: Andrey Konovalov <andreyknvl@...il.com>
> Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>
> Cc: Alexander Potapenko <glider@...gle.com>
> Cc: Dmitry Vyukov <dvyukov@...gle.com>
> Cc: Vincenzo Frascino <vincenzo.frascino@....com>
> ---
> include/linux/kasan.h | 5 +++--
> mm/kasan/generic.c | 19 +++++++++++++------
> mm/slub.c | 4 ++--
> 3 files changed, 18 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index d811b3d7d2a1..96c9d56e5510 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -302,7 +302,7 @@ static inline void kasan_unpoison_task_stack(struct task_struct *task) {}
>
> #ifdef CONFIG_KASAN_GENERIC
>
> -size_t kasan_metadata_size(struct kmem_cache *cache);
> +size_t kasan_metadata_size(struct kmem_cache *cache, bool in_object);
> slab_flags_t kasan_never_merge(void);
> void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
> slab_flags_t *flags);
> @@ -315,7 +315,8 @@ void kasan_record_aux_stack_noalloc(void *ptr);
> #else /* CONFIG_KASAN_GENERIC */
>
> /* Tag-based KASAN modes do not use per-object metadata. */
> -static inline size_t kasan_metadata_size(struct kmem_cache *cache)
> +static inline size_t kasan_metadata_size(struct kmem_cache *cache,
> + bool in_object)
> {
> return 0;
> }
> diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> index d8b5590f9484..b076f597a378 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -450,15 +450,22 @@ void kasan_init_object_meta(struct kmem_cache *cache, const void *object)
> __memset(alloc_meta, 0, sizeof(*alloc_meta));
> }
>
> -size_t kasan_metadata_size(struct kmem_cache *cache)
> +size_t kasan_metadata_size(struct kmem_cache *cache, bool in_object)
> {
> + struct kasan_cache *info = &cache->kasan_info;
> +
> if (!kasan_requires_meta())
> return 0;
> - return (cache->kasan_info.alloc_meta_offset ?
> - sizeof(struct kasan_alloc_meta) : 0) +
> - ((cache->kasan_info.free_meta_offset &&
> - cache->kasan_info.free_meta_offset != KASAN_NO_FREE_META) ?
> - sizeof(struct kasan_free_meta) : 0);
> +
> + if (in_object)
> + return (info->free_meta_offset ?
> + 0 : sizeof(struct kasan_free_meta));
> + else
> + return (info->alloc_meta_offset ?
> + sizeof(struct kasan_alloc_meta) : 0) +
> + ((info->free_meta_offset &&
> + info->free_meta_offset != KASAN_NO_FREE_META) ?
> + sizeof(struct kasan_free_meta) : 0);
> }
>
> static void __kasan_record_aux_stack(void *addr, bool can_alloc)
> diff --git a/mm/slub.c b/mm/slub.c
> index 17292c2d3eee..adff7553b54e 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -910,7 +910,7 @@ static void print_trailer(struct kmem_cache *s, struct slab *slab, u8 *p)
> if (slub_debug_orig_size(s))
> off += sizeof(unsigned int);
>
> - off += kasan_metadata_size(s);
> + off += kasan_metadata_size(s, false);
>
> if (off != size_from_object(s))
> /* Beginning of the filler is the free pointer */
> @@ -1070,7 +1070,7 @@ static int check_pad_bytes(struct kmem_cache *s, struct slab *slab, u8 *p)
> off += sizeof(unsigned int);
> }
>
> - off += kasan_metadata_size(s);
> + off += kasan_metadata_size(s, false);
>
> if (size_from_object(s) == off)
> return 1;
> --
> 2.34.1
>
Reviewed-by: Andrey Konovalov <andreyknvl@...il.com>
Thanks!
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