Re: [PATCH v3 2/4] kasan: record and print the free track

[Walter Wu <walter-zh.wu@mediatek.com>]

On Mon, 2020-05-18 at 12:18 +0200, Dmitry Vyukov wrote:
> On Mon, May 18, 2020 at 8:27 AM Walter Wu <walter-zh.wu@mediatek.com> wrote:
> >
> > Move free track from slub alloc meta-data to slub free meta-data in
> > order to make struct kasan_free_meta size is 16 bytes. It is a good
> > size because it is the minimal redzone size and a good number of
> > alignment.
> >
> > For free track in generic KASAN, we do the modification in struct
> > kasan_alloc_meta and kasan_free_meta:
> > - remove free track from kasan_alloc_meta.
> > - add free track into kasan_free_meta.
> >
> > [1]https://bugzilla.kernel.org/show_bug.cgi?id=198437
> >
> > Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com>
> > Suggested-by: Dmitry Vyukov <dvyukov@google.com>
> > Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> > Cc: Dmitry Vyukov <dvyukov@google.com>
> > Cc: Alexander Potapenko <glider@google.com>
> > ---
> >  mm/kasan/common.c  | 33 ++++++++++-----------------------
> >  mm/kasan/generic.c | 18 ++++++++++++++++++
> >  mm/kasan/kasan.h   |  7 +++++++
> >  mm/kasan/report.c  | 20 --------------------
> >  mm/kasan/tags.c    | 37 +++++++++++++++++++++++++++++++++++++
> >  5 files changed, 72 insertions(+), 43 deletions(-)
> >
> > diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> > index 8bc618289bb1..6500bc2bb70c 100644
> > --- a/mm/kasan/common.c
> > +++ b/mm/kasan/common.c
> > @@ -51,7 +51,7 @@ depot_stack_handle_t kasan_save_stack(gfp_t flags)
> >         return stack_depot_save(entries, nr_entries, flags);
> >  }
> >
> > -static inline void set_track(struct kasan_track *track, gfp_t flags)
> > +void kasan_set_track(struct kasan_track *track, gfp_t flags)
> >  {
> >         track->pid = current->pid;
> >         track->stack = kasan_save_stack(flags);
> > @@ -249,9 +249,7 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
> >         *size += sizeof(struct kasan_alloc_meta);
> >
> >         /* Add free meta. */
> > -       if (IS_ENABLED(CONFIG_KASAN_GENERIC) &&
> > -           (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
> > -            cache->object_size < sizeof(struct kasan_free_meta))) {
> > +       if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
> 
> Why do we need to increase object size unconditionally?
> We only store info in free track when the object is free, so I would
> assume we still can generally overlap free track and the object
> itself. We store free track at the same time we use the quarantine
> link, and the quarantine link was overlapped with the object just
> fine.
> With this change we indeed increase object size, which we do not want
> in general.
> 

If it doesn't add free meta, but we always store free track into the
object, Is it safe?

> 
> >                 cache->kasan_info.free_meta_offset = *size;
> >                 *size += sizeof(struct kasan_free_meta);
> >         }
> > @@ -299,24 +297,6 @@ struct kasan_free_meta *get_free_info(struct kmem_cache *cache,
> >         return (void *)object + cache->kasan_info.free_meta_offset;
> >  }
> >
> > -
> > -static void kasan_set_free_info(struct kmem_cache *cache,
> > -               void *object, u8 tag)
> > -{
> > -       struct kasan_alloc_meta *alloc_meta;
> > -       u8 idx = 0;
> > -
> > -       alloc_meta = get_alloc_info(cache, object);
> > -
> > -#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
> > -       idx = alloc_meta->free_track_idx;
> > -       alloc_meta->free_pointer_tag[idx] = tag;
> > -       alloc_meta->free_track_idx = (idx + 1) % KASAN_NR_FREE_STACKS;
> > -#endif
> > -
> > -       set_track(&alloc_meta->free_track[idx], GFP_NOWAIT);
> > -}
> > -
> >  void kasan_poison_slab(struct page *page)
> >  {
> >         unsigned long i;
> > @@ -396,6 +376,13 @@ void * __must_check kasan_init_slab_obj(struct kmem_cache *cache,
> >         alloc_info = get_alloc_info(cache, object);
> >         __memset(alloc_info, 0, sizeof(*alloc_info));
> >
> > +       if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
> > +               struct kasan_free_meta *free_info;
> > +
> > +               free_info = get_free_info(cache, object);
> > +               __memset(free_info, 0, sizeof(*free_info));
> 
> If we overlap free track with object, this will not be needed as well, right?
> 

Should we not consider those objects which have adding free meta? If
they exist, then we should init their meta data when object re-allocate.

struct kasan_free_meta {
    struct qlist_node quarantine_link;
    struct kasan_track free_track;
};


> > +       }
> > +
> >         if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
> >                 object = set_tag(object,
> >                                 assign_tag(cache, object, true, false));
> > @@ -492,7 +479,7 @@ static void *__kasan_kmalloc(struct kmem_cache *cache, const void *object,
> >                 KASAN_KMALLOC_REDZONE);
> >
> >         if (cache->flags & SLAB_KASAN)
> > -               set_track(&get_alloc_info(cache, object)->alloc_track, flags);
> > +               kasan_set_track(&get_alloc_info(cache, object)->alloc_track, flags);
> >
> >         return set_tag(object, tag);
> >  }
> > diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> > index 78d8e0a75a8a..988bc095b738 100644
> > --- a/mm/kasan/generic.c
> > +++ b/mm/kasan/generic.c
> > @@ -345,3 +345,21 @@ void kasan_record_aux_stack(void *addr)
> >                 alloc_info->rcu_stack[1] = alloc_info->rcu_stack[0];
> >         alloc_info->rcu_stack[0] = kasan_save_stack(GFP_NOWAIT);
> >  }
> > +
> > +void kasan_set_free_info(struct kmem_cache *cache,
> > +                               void *object, u8 tag)
> > +{
> > +       struct kasan_free_meta *free_meta;
> > +
> > +       free_meta = get_free_info(cache, object);
> > +       kasan_set_track(&free_meta->free_track, GFP_NOWAIT);
> > +}
> > +
> > +struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
> > +                               void *object, u8 tag)
> > +{
> > +       struct kasan_free_meta *free_meta;
> > +
> > +       free_meta = get_free_info(cache, object);
> > +       return &free_meta->free_track;
> > +}
> > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> > index 870c5dd07756..87ee3626b8b0 100644
> > --- a/mm/kasan/kasan.h
> > +++ b/mm/kasan/kasan.h
> > @@ -127,6 +127,9 @@ struct kasan_free_meta {
> >          * Otherwise it might be used for the allocator freelist.
> >          */
> >         struct qlist_node quarantine_link;
> > +#ifdef CONFIG_KASAN_GENERIC
> > +       struct kasan_track free_track;
> > +#endif
> >  };
> >
> >  struct kasan_alloc_meta *get_alloc_info(struct kmem_cache *cache,
> > @@ -168,6 +171,10 @@ void kasan_report_invalid_free(void *object, unsigned long ip);
> >  struct page *kasan_addr_to_page(const void *addr);
> >
> >  depot_stack_handle_t kasan_save_stack(gfp_t flags);
> > +void kasan_set_track(struct kasan_track *track, gfp_t flags);
> > +void kasan_set_free_info(struct kmem_cache *cache, void *object, u8 tag);
> > +struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
> > +                               void *object, u8 tag);
> >
> >  #if defined(CONFIG_KASAN_GENERIC) && \
> >         (defined(CONFIG_SLAB) || defined(CONFIG_SLUB))
> > diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> > index 5ee66cf7e27c..7e9f9f6d5e85 100644
> > --- a/mm/kasan/report.c
> > +++ b/mm/kasan/report.c
> > @@ -159,26 +159,6 @@ static void describe_object_addr(struct kmem_cache *cache, void *object,
> >                 (void *)(object_addr + cache->object_size));
> >  }
> >
> > -static struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
> > -               void *object, u8 tag)
> > -{
> > -       struct kasan_alloc_meta *alloc_meta;
> > -       int i = 0;
> > -
> > -       alloc_meta = get_alloc_info(cache, object);
> > -
> > -#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
> > -       for (i = 0; i < KASAN_NR_FREE_STACKS; i++) {
> > -               if (alloc_meta->free_pointer_tag[i] == tag)
> > -                       break;
> > -       }
> > -       if (i == KASAN_NR_FREE_STACKS)
> > -               i = alloc_meta->free_track_idx;
> > -#endif
> > -
> > -       return &alloc_meta->free_track[i];
> > -}
> > -
> >  #ifdef CONFIG_KASAN_GENERIC
> >  static void print_stack(depot_stack_handle_t stack)
> >  {
> > diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
> > index 25b7734e7013..201dee5d6ae0 100644
> > --- a/mm/kasan/tags.c
> > +++ b/mm/kasan/tags.c
> > @@ -162,3 +162,40 @@ void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
> >         kasan_poison_shadow((void *)addr, size, tag);
> >  }
> >  EXPORT_SYMBOL(__hwasan_tag_memory);
> > +
> > +void kasan_set_free_info(struct kmem_cache *cache,
> > +                               void *object, u8 tag)
> > +{
> > +       struct kasan_alloc_meta *alloc_meta;
> > +       u8 idx = 0;
> > +
> > +       alloc_meta = get_alloc_info(cache, object);
> > +
> > +#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
> > +       idx = alloc_meta->free_track_idx;
> > +       alloc_meta->free_pointer_tag[idx] = tag;
> > +       alloc_meta->free_track_idx = (idx + 1) % KASAN_NR_FREE_STACKS;
> > +#endif
> > +
> > +       kasan_set_track(&alloc_meta->free_track[idx], GFP_NOWAIT);
> > +}
> > +
> > +struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
> > +                               void *object, u8 tag)
> > +{
> > +       struct kasan_alloc_meta *alloc_meta;
> > +       int i = 0;
> > +
> > +       alloc_meta = get_alloc_info(cache, object);
> > +
> > +#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
> > +       for (i = 0; i < KASAN_NR_FREE_STACKS; i++) {
> > +               if (alloc_meta->free_pointer_tag[i] == tag)
> > +                       break;
> > +       }
> > +       if (i == KASAN_NR_FREE_STACKS)
> > +               i = alloc_meta->free_track_idx;
> > +#endif
> > +
> > +       return &alloc_meta->free_track[i];
> > +}
> > --
> > 2.18.0