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Date: Wed, 21 Sep 2022 20:02:45 +0800
From: Feng Tang <feng.tang@...el.com>
To: Andrey Konovalov <andreyknvl@...il.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>,
Jonathan Corbet <corbet@....net>,
"Hansen, Dave" <dave.hansen@...el.com>,
Linux Memory Management List <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>,
kasan-dev <kasan-dev@...glegroups.com>,
"Sang, Oliver" <oliver.sang@...el.com>
Subject: Re: [PATCH v6 3/4] mm: kasan: Add free_meta size info in struct
kasan_cache
Hi Andrey,
On Wed, Sep 21, 2022 at 03:20:58AM +0800, Andrey Konovalov wrote:
> On Tue, Sep 13, 2022 at 8:54 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]
> >
> > For better information for slab/slub, add free_meta's data size
> > into 'struct kasan_cache', so that its users can take right action
> > to avoid data conflict.
> >
> > [1]. https://lore.kernel.org/lkml/YuYm3dWwpZwH58Hu@xsang-OptiPlex-9020/
> > Reported-by: kernel test robot <oliver.sang@...el.com>
> > Signed-off-by: Feng Tang <feng.tang@...el.com>
> > Acked-by: Dmitry Vyukov <dvyukov@...gle.com>
> > ---
> > include/linux/kasan.h | 2 ++
> > mm/kasan/common.c | 2 ++
> > 2 files changed, 4 insertions(+)
> >
> > diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> > index b092277bf48d..49af9513e8ed 100644
> > --- a/include/linux/kasan.h
> > +++ b/include/linux/kasan.h
> > @@ -100,6 +100,8 @@ static inline bool kasan_has_integrated_init(void)
> > struct kasan_cache {
> > int alloc_meta_offset;
> > int free_meta_offset;
> > + /* size of free_meta data saved in object's data area */
> > + int free_meta_size;
> > bool is_kmalloc;
> > };
> >
> > diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> > index 69f583855c8b..0cb867e92524 100644
> > --- a/mm/kasan/common.c
> > +++ b/mm/kasan/common.c
> > @@ -201,6 +201,8 @@ void __kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
> > cache->kasan_info.free_meta_offset = KASAN_NO_FREE_META;
> > *size = ok_size;
> > }
> > + } else {
> > + cache->kasan_info.free_meta_size = sizeof(struct kasan_free_meta);
>
> Hi Feng,
>
> I just realized that we already have a function that exposes a similar
> functionality: kasan_metadata_size. However, this function returns the
> size of metadata that is stored in the redzone.
>
> I think, instead of adding free_meta_size, a better approach would be to:
>
> 1. Rename kasan_metadata_size to kasan_metadata_size_in_redzone (or
> something like that).
> 2. Add kasan_metadata_size_in_object with appropriate implementation
> and use that in your patches.
>
> This allows avoiding exposing KASAN-internal details such as what kind
> of fields the kasan_cache struct has to the common code.
Agree, it's better not touch the internal fields in slub code.
How about the following patch, it merge the 2 functions with one flag
indicating in meta data or object. (I'm fine with 2 separate functions)
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index b092277bf48d..0ad05a34e708 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -150,11 +150,12 @@ static __always_inline void kasan_cache_create_kmalloc(struct kmem_cache *cache)
__kasan_cache_create_kmalloc(cache);
}
-size_t __kasan_metadata_size(struct kmem_cache *cache);
-static __always_inline size_t kasan_metadata_size(struct kmem_cache *cache)
+size_t __kasan_meta_size(struct kmem_cache *cache, bool in_slab_object);
+static __always_inline size_t kasan_meta_size(struct kmem_cache *cache,
+ bool in_slab_object)
{
if (kasan_enabled())
- return __kasan_metadata_size(cache);
+ return __kasan_meta_size(cache, in_slab_object);
return 0;
}
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 69f583855c8b..2a8710461ebb 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -218,14 +218,21 @@ void __kasan_cache_create_kmalloc(struct kmem_cache *cache)
cache->kasan_info.is_kmalloc = true;
}
-size_t __kasan_metadata_size(struct kmem_cache *cache)
+size_t __kasan_meta_size(struct kmem_cache *cache, bool in_slab_object)
{
if (!kasan_stack_collection_enabled())
return 0;
- return (cache->kasan_info.alloc_meta_offset ?
- sizeof(struct kasan_alloc_meta) : 0) +
- (cache->kasan_info.free_meta_offset ?
- sizeof(struct kasan_free_meta) : 0);
+
+ if (in_slab_object)
+ return (cache->kasan_info.alloc_meta_offset == 0 ?
+ sizeof(struct kasan_alloc_meta) : 0) +
+ (cache->kasan_info.free_meta_offset ?
+ sizeof(struct kasan_free_meta) : 0);
+ else
+ return (cache->kasan_info.alloc_meta_offset == 0 ?
+ sizeof(struct kasan_alloc_meta) : 0) +
+ (cache->kasan_info.free_meta_offset ?
+ sizeof(struct kasan_free_meta) : 0);
}
struct kasan_alloc_meta *kasan_get_alloc_meta(struct kmem_cache *cache,
> Sorry for nor realizing this straight away.
>
> (Note that there's an upcoming patch that fixes a bug in
> kasan_metadata_size' implementation [1].)
Thanks for the note, will check this when making the formal patch.
- Feng
> Thanks!
>
> [1] https://lore.kernel.org/linux-mm/c7b316d30d90e5947eb8280f4dc78856a49298cf.1662411799.git.andreyknvl@google.com/
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