On Wed, May 6, 2020 at 7:22 AM Walter Wu <walter-zh.wu@xxxxxxxxxxxx> wrote: > > We add new KASAN_RCU_STACK_RECORD configuration option. It will move > free track from slub meta-data (struct kasan_alloc_meta) into freed object. > Because we hope this options doesn't enlarge slub meta-data size. > > This option doesn't enlarge struct kasan_alloc_meta size. > - add two call_rcu() call stack into kasan_alloc_meta, size is 8 bytes. > - remove free track from kasan_alloc_meta, size is 8 bytes. > > This option is only suitable for generic KASAN, because we move free track > into the freed object, so free track is valid information only when it > exists in quarantine. If the object is in-use state, then the KASAN report > doesn't print call_rcu() free track information. > > [1]https://bugzilla.kernel.org/show_bug.cgi?id=198437 > > Signed-off-by: Walter Wu <walter-zh.wu@xxxxxxxxxxxx> > Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> > Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > Cc: Alexander Potapenko <glider@xxxxxxxxxx> > --- > mm/kasan/common.c | 10 +++++++++- > mm/kasan/report.c | 24 +++++++++++++++++++++--- > 2 files changed, 30 insertions(+), 4 deletions(-) > > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > index 32d422bdf127..13ec03e225a7 100644 > --- a/mm/kasan/common.c > +++ b/mm/kasan/common.c > @@ -321,8 +321,15 @@ void kasan_record_callrcu(void *addr) > /* record last call_rcu() call stack */ > alloc_info->rcu_free_stack[1] = save_stack(GFP_NOWAIT); > } > -#endif > > +static void kasan_set_free_info(struct kmem_cache *cache, > + void *object, u8 tag) > +{ > + /* store free track into freed object */ > + set_track((struct kasan_track *)(object + BYTES_PER_WORD), GFP_NOWAIT); > +} > + > +#else > static void kasan_set_free_info(struct kmem_cache *cache, > void *object, u8 tag) > { > @@ -339,6 +346,7 @@ static void kasan_set_free_info(struct kmem_cache *cache, > > set_track(&alloc_meta->free_track[idx], GFP_NOWAIT); > } > +#endif > > void kasan_poison_slab(struct page *page) > { > diff --git a/mm/kasan/report.c b/mm/kasan/report.c > index 7aaccc70b65b..f2b0c6b9dffa 100644 > --- a/mm/kasan/report.c > +++ b/mm/kasan/report.c > @@ -175,8 +175,23 @@ static void kasan_print_rcu_free_stack(struct kasan_alloc_meta *alloc_info) > print_track(&free_track, "Last call_rcu() call stack", true); > pr_err("\n"); > } > -#endif > > +static struct kasan_track *kasan_get_free_track(struct kmem_cache *cache, > + void *object, u8 tag, const void *addr) > +{ > + u8 *shadow_addr = (u8 *)kasan_mem_to_shadow(addr); > + > + /* > + * Only the freed object can get free track, > + * because free track information is stored to freed object. > + */ > + if (*shadow_addr == KASAN_KMALLOC_FREE) > + return (struct kasan_track *)(object + BYTES_PER_WORD); Humm... the other patch defines BYTES_PER_WORD as 4... I would assume seeing 8 (or sizeof(long)) here. Why 4? Have you tested all 4 modes (RCU/no-RCU x SLAB/SLUB)? As far as I remember one of the allocators stored something in the object. Also, does this work with objects with ctors and slabs destroyed by rcu? kasan_track may smash other things in these cases. Have you looked at the KASAN implementation when free_track was removed? That may have useful details :) > + else > + return NULL; > +} > + > +#else > static struct kasan_track *kasan_get_free_track(struct kmem_cache *cache, > void *object, u8 tag, const void *addr) > { > @@ -196,6 +211,7 @@ static struct kasan_track *kasan_get_free_track(struct kmem_cache *cache, > > return &alloc_meta->free_track[i]; > } > +#endif > > static void describe_object(struct kmem_cache *cache, void *object, > const void *addr, u8 tag) > @@ -208,8 +224,10 @@ static void describe_object(struct kmem_cache *cache, void *object, > print_track(&alloc_info->alloc_track, "Allocated", false); > pr_err("\n"); > free_track = kasan_get_free_track(cache, object, tag, addr); > - print_track(free_track, "Freed", false); > - pr_err("\n"); > + if (free_track) { > + print_track(free_track, "Freed", false); > + pr_err("\n"); > + } > #ifdef CONFIG_KASAN_RCU_STACK_RECORD > kasan_print_rcu_free_stack(alloc_info); > #endif > -- > 2.18.0 > > -- > You received this message because you are subscribed to the Google Groups "kasan-dev" group. > To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+unsubscribe@xxxxxxxxxxxxxxxx. > To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/20200506052155.14515-1-walter-zh.wu%40mediatek.com.
