On 11/10/22 13:57, Feng Tang wrote: > On Thu, Nov 10, 2022 at 11:20:34AM +0800, Tang, Feng wrote: >> On Wed, Nov 09, 2022 at 03:28:19PM +0100, Vlastimil Babka wrote: > [...] >> > > + /* >> > > + * 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) && >> > >> > Shouldn't we check SLAB_RED_ZONE instead? Otherwise a debugging could be >> > specified so that SLAB_RED_ZONE is set but SLAB_STORE_USER? >> >> Thanks for the catch! >> >> I will add check for SLAB_RED_ZONE. The SLAB_STORE_USER is for >> checking whether 'orig_size' field exists. In earlier discussion, >> we make 'orig_size' depend on STORE_USER, https://lore.kernel.org/lkml/1b0fa66c-f855-1c00-e024-b2b823b18678@xxxxxxx/ > > Below is the updated patch, please review, thanks! Thanks, grabbing it including Andrey's review, with a small change below: > - Feng > > -----8>---- > From b2a92f0c2518ef80fcda340f1ad37b418ee32d85 Mon Sep 17 00:00:00 2001 > From: Feng Tang <feng.tang@xxxxxxxxx> > Date: Thu, 20 Oct 2022 20:47:31 +0800 > Subject: [PATCH 1/3] mm/slub: only zero requested size of buffer for kzalloc > when debug enabled > > 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> > Acked-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> > --- > mm/slab.c | 7 ++++--- > mm/slab.h | 19 +++++++++++++++++-- > mm/slub.c | 10 +++++++--- > 3 files changed, 28 insertions(+), 8 deletions(-) > > diff --git a/mm/slab.c b/mm/slab.c > index 4b265174b6d5..1eddec4a50e4 100644 > --- a/mm/slab.c > +++ b/mm/slab.c > @@ -3258,7 +3258,8 @@ 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; > } > > @@ -3511,13 +3512,13 @@ 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 8c4aafb00bd6..2551214392c7 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -730,12 +730,27 @@ 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_RED_ZONE) && Combined the two above to: if (kmem_cache_debug_flags(s, SLAB_STORE_USER | SLAB_RED_ZONE) > + (s->flags & SLAB_KMALLOC)) > + zero_size = orig_size; > + > /* > * As memory initialization might be integrated into KASAN, > * kasan_slab_alloc and initialization memset must be > @@ -746,7 +761,7 @@ 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 0a14e7bc278c..13490f317f5f 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -3387,7 +3387,11 @@ 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 might be zeroed instead of s->object_size > + */ > + slab_post_alloc_hook(s, objcg, gfpflags, 1, &object, init, orig_size); > > return object; > } > @@ -3844,11 +3848,11 @@ 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; > }
