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Date: Sun, 25 Sep 2022 19:26:41 +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
On Sun, Sep 25, 2022 at 02:05:04AM +0800, Andrey Konovalov wrote:
> On Wed, Sep 21, 2022 at 2:03 PM Feng Tang <feng.tang@...el.com> wrote:
> >
> > 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)
>
> The overall approach sounds good. See some comments below.
>
> > 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)
>
> I would keep the name as kasan_metadata_size as it's more clear to
> external users but rename in_slab_object to in_object to make the
> declaration shorter.
Make sense to me, will do.
[...]
> > + 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);
>
> Something weird here: both if and else cases are the same.
Yes, will fix it.
> The change also needs to be rebased onto [1].
>
> Thanks!
>
> [1] https://lore.kernel.org/linux-mm/c7b316d30d90e5947eb8280f4dc78856a49298cf.1662411799.git.andreyknvl@google.com/
I noticed this has been merged to -mm tree's 'mm-everything' branch,
so following is the patch againt that. Thanks!
One thing I'm not very sure is, to check 'in-object' kasan's meta
size, I didn't check 'alloc_meta_offset', as from the code reading
the alloc_meta is never put inside slab object data area.
Thanks,
Feng
---8<---
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..5a806f9b9466 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 ce8310e131b3..a75c21a0da8b 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -887,7 +887,7 @@ static void print_trailer(struct kmem_cache *s, struct slab *slab, u8 *p)
if (s->flags & SLAB_STORE_USER)
off += 2 * sizeof(struct track);
- 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 */
@@ -1042,7 +1042,7 @@ static int check_pad_bytes(struct kmem_cache *s, struct slab *slab, u8 *p)
/* We also have user information there */
off += 2 * sizeof(struct track);
- off += kasan_metadata_size(s);
+ off += kasan_metadata_size(s, false);
if (size_from_object(s) == off)
return 1;
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