On Fri, Oct 21, 2022 at 11:24:03AM +0800, Feng Tang 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 redzone 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 when debug is enabled. (Thanks to Kees Cook's effort to > sanitize all ksize() user cases [1], this won't be a big issue). > > [1]. https://lore.kernel.org/all/20220922031013.2150682-1-keescook@xxxxxxxxxxxx/#r > Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx> > --- > mm/slab.c | 7 ++++--- > mm/slab.h | 18 ++++++++++++++++-- > mm/slub.c | 10 +++++++--- > 3 files changed, 27 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 0202a8c2f0d2..8b4ee02fc14a 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -720,12 +720,26 @@ 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) > { > + unsigned int zero_size = s->object_size; > size_t i; > > flags &= gfp_allowed_mask; > > + /* > + * For kmalloc object, the allocated memory size(object_size) is likely > + * larger than the requested size(orig_size). If redzone check is > + * enabled for the extra space, don't zero it, as it will be redzoned > + * soon. The redzone operation for this extra space could be seen as a > + * replacement of current poisoning under certain debug option, and > + * won't break other sanity checks. > + */ > + if (kmem_cache_debug_flags(s, SLAB_STORE_USER) && > + (s->flags & SLAB_KMALLOC)) > + zero_size = orig_size; > + > /* > * As memory initialization might be integrated into KASAN, > * kasan_slab_alloc and initialization memset must be > @@ -736,7 +750,7 @@ 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, zero_size); > kmemleak_alloc_recursive(p[i], s->object_size, 1, > s->flags, flags); > kmsan_slab_alloc(s, p[i], flags); > diff --git a/mm/slub.c b/mm/slub.c > index 12354fb8d6e4..17292c2d3eee 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -3395,7 +3395,11 @@ 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; > } > @@ -3852,11 +3856,11 @@ 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 Looks good to me. Acked-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> -- Thanks, Hyeonggon
