On Wed, Sep 7, 2022 at 9:10 AM Feng Tang <feng.tang@xxxxxxxxx> wrote:
>
> 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.
>
> For kzalloc users who will call ksize() later and utilize this
> extra space, please be aware that the space is not zeroed any
> more.
>
> Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
> ---
> mm/slab.c | 6 +++---
> mm/slab.h | 9 +++++++--
> mm/slub.c | 6 +++---
> 3 files changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/mm/slab.c b/mm/slab.c
> index a5486ff8362a..73ecaa7066e1 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3253,7 +3253,7 @@ 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, 0);
> return objp;
> }
>
> @@ -3506,13 +3506,13 @@ 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), 0);
> /* 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, 0);
> kmem_cache_free_bulk(s, i, p);
> return 0;
> }
> diff --git a/mm/slab.h b/mm/slab.h
> index d0ef9dd44b71..20f9e2a9814f 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -730,12 +730,17 @@ 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;
>
> flags &= gfp_allowed_mask;
>
> + /* If original request size(kmalloc) is not set, use object_size */
> + if (!orig_size)
> + orig_size = s->object_size;
> +
> /*
> * As memory initialization might be integrated into KASAN,
> * kasan_slab_alloc and initialization memset must be
> @@ -746,7 +751,7 @@ 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);
Arguably, with slab_want_init_on_alloc(), all allocated memory should
be zeroed to prevent possibility of info-leaks, even unused paddings.
Perhaps, Alexander can give his opinion here.
Thanks!
> kmemleak_alloc_recursive(p[i], s->object_size, 1,
> s->flags, flags);
> }
> diff --git a/mm/slub.c b/mm/slub.c
> index effd994438e6..f523601d3fcf 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3376,7 +3376,7 @@ 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);
> + slab_post_alloc_hook(s, objcg, gfpflags, 1, &object, init, orig_size);
>
> return object;
> }
> @@ -3833,11 +3833,11 @@ 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), 0);
> 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, 0);
> kmem_cache_free_bulk(s, i, p);
> return 0;
> }
> --
> 2.34.1
>
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