On Fri, 1 Jul 2022 at 16:23, 'Alexander Potapenko' via kasan-dev <kasan-dev@xxxxxxxxxxxxxxxx> wrote: > > In order to report uninitialized memory coming from heap allocations > KMSAN has to poison them unless they're created with __GFP_ZERO. > > It's handy that we need KMSAN hooks in the places where > init_on_alloc/init_on_free initialization is performed. > > In addition, we apply __no_kmsan_checks to get_freepointer_safe() to > suppress reports when accessing freelist pointers that reside in freed > objects. > > Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx> Reviewed-by: Marco Elver <elver@xxxxxxxxxx> But see comment below. > --- > v2: > -- move the implementation of SLUB hooks here > > v4: > -- change sizeof(type) to sizeof(*ptr) > -- swap mm: and kmsan: in the subject > -- get rid of kmsan_init(), replace it with __no_kmsan_checks > > Link: https://linux-review.googlesource.com/id/I6954b386c5c5d7f99f48bb6cbcc74b75136ce86e > --- > include/linux/kmsan.h | 57 ++++++++++++++++++++++++++++++ > mm/kmsan/hooks.c | 80 +++++++++++++++++++++++++++++++++++++++++++ > mm/slab.h | 1 + > mm/slub.c | 18 ++++++++++ > 4 files changed, 156 insertions(+) > > diff --git a/include/linux/kmsan.h b/include/linux/kmsan.h > index 699fe4f5b3bee..fd76cea338878 100644 > --- a/include/linux/kmsan.h > +++ b/include/linux/kmsan.h > @@ -15,6 +15,7 @@ > #include <linux/types.h> > > struct page; > +struct kmem_cache; > > #ifdef CONFIG_KMSAN > > @@ -72,6 +73,44 @@ void kmsan_free_page(struct page *page, unsigned int order); > */ > void kmsan_copy_page_meta(struct page *dst, struct page *src); > > +/** > + * kmsan_slab_alloc() - Notify KMSAN about a slab allocation. > + * @s: slab cache the object belongs to. > + * @object: object pointer. > + * @flags: GFP flags passed to the allocator. > + * > + * Depending on cache flags and GFP flags, KMSAN sets up the metadata of the > + * newly created object, marking it as initialized or uninitialized. > + */ > +void kmsan_slab_alloc(struct kmem_cache *s, void *object, gfp_t flags); > + > +/** > + * kmsan_slab_free() - Notify KMSAN about a slab deallocation. > + * @s: slab cache the object belongs to. > + * @object: object pointer. > + * > + * KMSAN marks the freed object as uninitialized. > + */ > +void kmsan_slab_free(struct kmem_cache *s, void *object); > + > +/** > + * kmsan_kmalloc_large() - Notify KMSAN about a large slab allocation. > + * @ptr: object pointer. > + * @size: object size. > + * @flags: GFP flags passed to the allocator. > + * > + * Similar to kmsan_slab_alloc(), but for large allocations. > + */ > +void kmsan_kmalloc_large(const void *ptr, size_t size, gfp_t flags); > + > +/** > + * kmsan_kfree_large() - Notify KMSAN about a large slab deallocation. > + * @ptr: object pointer. > + * > + * Similar to kmsan_slab_free(), but for large allocations. > + */ > +void kmsan_kfree_large(const void *ptr); > + > /** > * kmsan_map_kernel_range_noflush() - Notify KMSAN about a vmap. > * @start: start of vmapped range. > @@ -138,6 +177,24 @@ static inline void kmsan_copy_page_meta(struct page *dst, struct page *src) > { > } > > +static inline void kmsan_slab_alloc(struct kmem_cache *s, void *object, > + gfp_t flags) > +{ > +} > + > +static inline void kmsan_slab_free(struct kmem_cache *s, void *object) > +{ > +} > + > +static inline void kmsan_kmalloc_large(const void *ptr, size_t size, > + gfp_t flags) > +{ > +} > + > +static inline void kmsan_kfree_large(const void *ptr) > +{ > +} > + > static inline void kmsan_vmap_pages_range_noflush(unsigned long start, > unsigned long end, > pgprot_t prot, > diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c > index 070756be70e3a..052e17b7a717d 100644 > --- a/mm/kmsan/hooks.c > +++ b/mm/kmsan/hooks.c > @@ -26,6 +26,86 @@ > * skipping effects of functions like memset() inside instrumented code. > */ > > +void kmsan_slab_alloc(struct kmem_cache *s, void *object, gfp_t flags) > +{ > + if (unlikely(object == NULL)) > + return; > + if (!kmsan_enabled || kmsan_in_runtime()) > + return; > + /* > + * There's a ctor or this is an RCU cache - do nothing. The memory > + * status hasn't changed since last use. > + */ > + if (s->ctor || (s->flags & SLAB_TYPESAFE_BY_RCU)) > + return; > + > + kmsan_enter_runtime(); > + if (flags & __GFP_ZERO) > + kmsan_internal_unpoison_memory(object, s->object_size, > + KMSAN_POISON_CHECK); > + else > + kmsan_internal_poison_memory(object, s->object_size, flags, > + KMSAN_POISON_CHECK); > + kmsan_leave_runtime(); > +} > +EXPORT_SYMBOL(kmsan_slab_alloc); > + > +void kmsan_slab_free(struct kmem_cache *s, void *object) > +{ > + if (!kmsan_enabled || kmsan_in_runtime()) > + return; > + > + /* RCU slabs could be legally used after free within the RCU period */ > + if (unlikely(s->flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON))) > + return; > + /* > + * If there's a constructor, freed memory must remain in the same state > + * until the next allocation. We cannot save its state to detect > + * use-after-free bugs, instead we just keep it unpoisoned. > + */ > + if (s->ctor) > + return; > + kmsan_enter_runtime(); > + kmsan_internal_poison_memory(object, s->object_size, GFP_KERNEL, > + KMSAN_POISON_CHECK | KMSAN_POISON_FREE); > + kmsan_leave_runtime(); > +} > +EXPORT_SYMBOL(kmsan_slab_free); > + > +void kmsan_kmalloc_large(const void *ptr, size_t size, gfp_t flags) > +{ > + if (unlikely(ptr == NULL)) > + return; > + if (!kmsan_enabled || kmsan_in_runtime()) > + return; > + kmsan_enter_runtime(); > + if (flags & __GFP_ZERO) > + kmsan_internal_unpoison_memory((void *)ptr, size, > + /*checked*/ true); > + else > + kmsan_internal_poison_memory((void *)ptr, size, flags, > + KMSAN_POISON_CHECK); > + kmsan_leave_runtime(); > +} > +EXPORT_SYMBOL(kmsan_kmalloc_large); > + > +void kmsan_kfree_large(const void *ptr) > +{ > + struct page *page; > + > + if (!kmsan_enabled || kmsan_in_runtime()) > + return; > + kmsan_enter_runtime(); > + page = virt_to_head_page((void *)ptr); > + KMSAN_WARN_ON(ptr != page_address(page)); > + kmsan_internal_poison_memory((void *)ptr, > + PAGE_SIZE << compound_order(page), > + GFP_KERNEL, > + KMSAN_POISON_CHECK | KMSAN_POISON_FREE); > + kmsan_leave_runtime(); > +} > +EXPORT_SYMBOL(kmsan_kfree_large); > + > static unsigned long vmalloc_shadow(unsigned long addr) > { > return (unsigned long)kmsan_get_metadata((void *)addr, > diff --git a/mm/slab.h b/mm/slab.h > index db9fb5c8dae73..d0de8195873d8 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -752,6 +752,7 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s, > memset(p[i], 0, s->object_size); > kmemleak_alloc_recursive(p[i], s->object_size, 1, > s->flags, flags); > + kmsan_slab_alloc(s, p[i], flags); > } > > memcg_slab_post_alloc_hook(s, objcg, flags, size, p); > diff --git a/mm/slub.c b/mm/slub.c > index b1281b8654bd3..b8b601f165087 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -22,6 +22,7 @@ > #include <linux/proc_fs.h> > #include <linux/seq_file.h> > #include <linux/kasan.h> > +#include <linux/kmsan.h> > #include <linux/cpu.h> > #include <linux/cpuset.h> > #include <linux/mempolicy.h> > @@ -359,6 +360,17 @@ static void prefetch_freepointer(const struct kmem_cache *s, void *object) > prefetchw(object + s->offset); > } > > +/* > + * When running under KMSAN, get_freepointer_safe() may return an uninitialized > + * pointer value in the case the current thread loses the race for the next > + * memory chunk in the freelist. In that case this_cpu_cmpxchg_double() in > + * slab_alloc_node() will fail, so the uninitialized value won't be used, but > + * KMSAN will still check all arguments of cmpxchg because of imperfect > + * handling of inline assembly. > + * To work around this problem, we apply __no_kmsan_checks to ensure that > + * get_freepointer_safe() returns initialized memory. > + */ > +__no_kmsan_checks > static inline void *get_freepointer_safe(struct kmem_cache *s, void *object) > { > unsigned long freepointer_addr; > @@ -1709,6 +1721,7 @@ static inline void *kmalloc_large_node_hook(void *ptr, size_t size, gfp_t flags) > ptr = kasan_kmalloc_large(ptr, size, flags); > /* As ptr might get tagged, call kmemleak hook after KASAN. */ > kmemleak_alloc(ptr, size, 1, flags); > + kmsan_kmalloc_large(ptr, size, flags); > return ptr; > } > > @@ -1716,12 +1729,14 @@ static __always_inline void kfree_hook(void *x) > { > kmemleak_free(x); > kasan_kfree_large(x); > + kmsan_kfree_large(x); > } > > static __always_inline bool slab_free_hook(struct kmem_cache *s, > void *x, bool init) > { > kmemleak_free_recursive(x, s->flags); > + kmsan_slab_free(s, x); > > debug_check_no_locks_freed(x, s->object_size); > > @@ -3756,6 +3771,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size, > */ > slab_post_alloc_hook(s, objcg, flags, size, p, > slab_want_init_on_alloc(flags, s)); > + Remove unnecessary whitespace change.
