On Mon, Sep 17, 2018 at 8:59 PM, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote: > On Wed, Sep 12, 2018 at 6:21 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: >> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote: > >>> +void *khwasan_preset_slub_tag(struct kmem_cache *cache, const void *addr) >> >> Can't we do this in the existing kasan_init_slab_obj() hook? It looks >> like it should do exactly this -- allow any one-time initialization >> for objects. We could extend it to accept index and return a new >> pointer. >> If that does not work for some reason, I would try to at least unify >> the hook for slab/slub, e.g. pass idx=-1 from slub and then use >> random_tag(). >> It also seems that we do preset tag for slab multiple times (from >> slab_get_obj()). Using kasan_init_slab_obj() should resolve this too >> (hopefully we don't call it multiple times). > > The issue is that SLAB stores freelist as an array of indexes instead > of using an actual linked list like SLUB. So you can't store the tag > in the pointer while the object is in the freelist, since there's no > pointer. And, technically, we don't preset tags for SLAB, we just use > the id as the tag every time a pointer is used, so perhaps we should > rename the callback. As to unifying the callbacks, sure, we can do > that. As per offline discussion: potentially we can use kasan_init_slab_obj() if we add tag in kmalloc hook by using obj_to_idx().
