On Tue, Sep 13, 2022 at 8:54 AM Feng Tang <feng.tang@xxxxxxxxx> 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@xxxxxxxxx> > Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx> > Acked-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > --- > 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. 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! [1] https://lore.kernel.org/linux-mm/c7b316d30d90e5947eb8280f4dc78856a49298cf.1662411799.git.andreyknvl@xxxxxxxxxx/ > } > > /* Calculate size with optimal redzone. */ > -- > 2.34.1 >
