On Wed, Sep 19, 2018 at 8:54 PM, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote: > An object constructor can initialize pointers within this objects based on > the address of the object. Since the object address might be tagged, we > need to assign a tag before calling constructor. > > The implemented approach is to assign tags to objects with constructors > when a slab is allocated and call constructors once as usual. The > downside is that such object would always have the same tag when it is > reallocated, so we won't catch use-after-frees on it. > > Also pressign tags for objects from SLAB_TYPESAFE_BY_RCU caches, since > they can be validy accessed after having been freed. > > Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> > --- > mm/slab.c | 2 +- > mm/slub.c | 24 ++++++++++++++---------- > 2 files changed, 15 insertions(+), 11 deletions(-) > > diff --git a/mm/slab.c b/mm/slab.c > index 6fdca9ec2ea4..fe0ddf08aa2c 100644 > --- a/mm/slab.c > +++ b/mm/slab.c > @@ -2574,7 +2574,7 @@ static void cache_init_objs(struct kmem_cache *cachep, > > for (i = 0; i < cachep->num; i++) { > objp = index_to_obj(cachep, page, i); > - kasan_init_slab_obj(cachep, objp); > + objp = kasan_init_slab_obj(cachep, objp); > > /* constructor could break poison info */ > if (DEBUG == 0 && cachep->ctor) { > diff --git a/mm/slub.c b/mm/slub.c > index c4d5f4442ff1..75fc76e42a1e 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -1413,16 +1413,17 @@ static inline bool slab_free_freelist_hook(struct kmem_cache *s, > #endif > } > > -static void setup_object(struct kmem_cache *s, struct page *page, > +static void *setup_object(struct kmem_cache *s, struct page *page, > void *object) > { > setup_object_debug(s, page, object); > - kasan_init_slab_obj(s, object); > + object = kasan_init_slab_obj(s, object); > if (unlikely(s->ctor)) { > kasan_unpoison_object_data(s, object); > s->ctor(object); > kasan_poison_object_data(s, object); > } > + return object; > } > > /* > @@ -1530,16 +1531,16 @@ static bool shuffle_freelist(struct kmem_cache *s, struct page *page) > /* First entry is used as the base of the freelist */ > cur = next_freelist_entry(s, page, &pos, start, page_limit, > freelist_count); > + cur = setup_object(s, page, cur); > page->freelist = cur; > > for (idx = 1; idx < page->objects; idx++) { > - setup_object(s, page, cur); > next = next_freelist_entry(s, page, &pos, start, page_limit, > freelist_count); > + next = setup_object(s, page, next); > set_freepointer(s, cur, next); > cur = next; > } > - setup_object(s, page, cur); > set_freepointer(s, cur, NULL); > > return true; > @@ -1561,7 +1562,7 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node) > struct page *page; > struct kmem_cache_order_objects oo = s->oo; > gfp_t alloc_gfp; > - void *start, *p; > + void *start, *p, *next; > int idx, order; > bool shuffle; > > @@ -1613,13 +1614,16 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node) > > if (!shuffle) { > for_each_object_idx(p, idx, s, start, page->objects) { > - setup_object(s, page, p); > - if (likely(idx < page->objects)) > - set_freepointer(s, p, p + s->size); > - else > + if (likely(idx < page->objects)) { > + next = p + s->size; > + next = setup_object(s, page, next); > + set_freepointer(s, p, next); > + } else > set_freepointer(s, p, NULL); > } > - page->freelist = fixup_red_left(s, start); > + start = fixup_red_left(s, start); > + start = setup_object(s, page, start); > + page->freelist = start; > } Just want to double-check that this is correct. We now do an additional setup_object call after the loop, but we do 1 less in the loop. So total number of calls should be the same, right? However, after the loop we call setup_object for the first object (?), but inside of the loop we skip the call for the last object (?). Am I missing something, or we call ctor twice for the last object and don't call it for the first one? > page->inuse = page->objects; > -- > 2.19.0.397.gdd90340f6a-goog