On Wed, Nov 09, 2022 at 03:28:19PM +0100, Vlastimil Babka wrote: > On 10/21/22 05:24, 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> > > --- [...] > > 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) && > > 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/ > > + (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 > > s/will be/might be/ because it depends on the debugging? Yes, will change. Thanks, Feng
