On Tue, Sep 13, 2022 at 8:54 AM Feng Tang <feng.tang@xxxxxxxxx> wrote:
>
Hi Feng,
> kzalloc/kmalloc will round up the request size to a fixed size
> (mostly power of 2), so the allocated memory could be more than
> requested. Currently kzalloc family APIs will zero all the
> allocated memory.
>
> To detect out-of-bound usage of the extra allocated memory, only
> zero the requested part, so that sanity check could be added to
> the extra space later.
I still don't like the idea of only zeroing the requested memory and
not the whole object. Considering potential info-leak vulnerabilities.
Can we only do this when SLAB_DEBUG is enabled?
> Performance wise, smaller zeroing length also brings shorter
> execution time, as shown from test data on various server/desktop
> platforms.
>
> For kzalloc users who will call ksize() later and utilize this
> extra space, please be aware that the space is not zeroed any
> more.
CC Kees
>
> Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
> ---
> mm/slab.c | 7 ++++---
> mm/slab.h | 5 +++--
> mm/slub.c | 10 +++++++---
> 3 files changed, 14 insertions(+), 8 deletions(-)
>
> diff --git a/mm/slab.c b/mm/slab.c
> index a5486ff8362a..4594de0e3d6b 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3253,7 +3253,8 @@ slab_alloc_node(struct kmem_cache *cachep, struct list_lru *lru, gfp_t flags,
> init = slab_want_init_on_alloc(flags, cachep);
>
> out:
> - slab_post_alloc_hook(cachep, objcg, flags, 1, &objp, init);
> + slab_post_alloc_hook(cachep, objcg, flags, 1, &objp, init,
> + cachep->object_size);
> return objp;
> }
>
> @@ -3506,13 +3507,13 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
> * Done outside of the IRQ disabled section.
> */
> slab_post_alloc_hook(s, objcg, flags, size, p,
> - slab_want_init_on_alloc(flags, s));
> + slab_want_init_on_alloc(flags, s), s->object_size);
> /* FIXME: Trace call missing. Christoph would like a bulk variant */
> return size;
> error:
> local_irq_enable();
> cache_alloc_debugcheck_after_bulk(s, flags, i, p, _RET_IP_);
> - slab_post_alloc_hook(s, objcg, flags, i, p, false);
> + slab_post_alloc_hook(s, objcg, flags, i, p, false, s->object_size);
> kmem_cache_free_bulk(s, i, p);
> return 0;
> }
> diff --git a/mm/slab.h b/mm/slab.h
> index d0ef9dd44b71..3cf5adf63f48 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -730,7 +730,8 @@ static inline struct kmem_cache *slab_pre_alloc_hook(struct kmem_cache *s,
>
> static inline void slab_post_alloc_hook(struct kmem_cache *s,
> struct obj_cgroup *objcg, gfp_t flags,
> - size_t size, void **p, bool init)
> + size_t size, void **p, bool init,
> + unsigned int orig_size)
> {
> size_t i;
>
> @@ -746,7 +747,7 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s,
> for (i = 0; i < size; i++) {
> p[i] = kasan_slab_alloc(s, p[i], flags, init);
> if (p[i] && init && !kasan_has_integrated_init())
> - memset(p[i], 0, s->object_size);
> + memset(p[i], 0, orig_size);
Note that when KASAN is enabled and has integrated init, it will
initialize the whole object, which leads to an inconsistency with this
change.
> kmemleak_alloc_recursive(p[i], s->object_size, 1,
> s->flags, flags);
> }
> diff --git a/mm/slub.c b/mm/slub.c
> index c8ba16b3a4db..6f823e99d8b4 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3376,7 +3376,11 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s, struct list_l
> init = slab_want_init_on_alloc(gfpflags, s);
>
> out:
> - slab_post_alloc_hook(s, objcg, gfpflags, 1, &object, init);
> + /*
> + * When init equals 'true', like for kzalloc() family, only
> + * @orig_size bytes will be zeroed instead of s->object_size
> + */
> + slab_post_alloc_hook(s, objcg, gfpflags, 1, &object, init, orig_size);
>
> return object;
> }
> @@ -3833,11 +3837,11 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
> * Done outside of the IRQ disabled fastpath loop.
> */
> slab_post_alloc_hook(s, objcg, flags, size, p,
> - slab_want_init_on_alloc(flags, s));
> + slab_want_init_on_alloc(flags, s), s->object_size);
> return i;
> error:
> slub_put_cpu_ptr(s->cpu_slab);
> - slab_post_alloc_hook(s, objcg, flags, i, p, false);
> + slab_post_alloc_hook(s, objcg, flags, i, p, false, s->object_size);
> kmem_cache_free_bulk(s, i, p);
> return 0;
> }
> --
> 2.34.1
>
