From 9ce67395f5a0cdec6ce152d26bfda13b98b25c01 Mon Sep 17 00:00:00 2001 From: Feng Tang Date: Fri, 21 Oct 2022 11:24:03 +0800 Subject: 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@chromium.org/#r Signed-off-by: Feng Tang Acked-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> Reviewed-by: Andrey Konovalov Signed-off-by: Vlastimil Babka --- mm/slub.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) (limited to 'mm/slub.c') diff --git a/mm/slub.c b/mm/slub.c index 157527d7101b..ecc44067625c 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3395,7 +3395,11 @@ redo: 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; } @@ -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; } -- cgit v1.2.1 From 5d1ba31087627423dfb2bd87badd62361701997b Mon Sep 17 00:00:00 2001 From: Feng Tang Date: Fri, 21 Oct 2022 11:24:04 +0800 Subject: mm: kasan: Extend kasan_metadata_size() to also cover in-object size When kasan is enabled for slab/slub, it may save kasan' free_meta data in the former part of slab object data area in slab object's free path, which works fine. There is ongoing effort to extend slub's debug function which will redzone the latter part of kmalloc object area, and when both of the debug are enabled, there is possible conflict, especially when the kmalloc object has small size, as caught by 0Day bot [1]. To solve it, slub code needs to know the in-object kasan's meta data size. Currently, there is existing kasan_metadata_size() which returns the kasan's metadata size inside slub's metadata area, so extend it to also cover the in-object meta size by adding a boolean flag 'in_object'. There is no functional change to existing code logic. [1]. https://lore.kernel.org/lkml/YuYm3dWwpZwH58Hu@xsang-OptiPlex-9020/ Reported-by: kernel test robot Suggested-by: Andrey Konovalov Signed-off-by: Feng Tang Reviewed-by: Andrey Konovalov Cc: Andrey Ryabinin Cc: Alexander Potapenko Cc: Dmitry Vyukov Cc: Vincenzo Frascino Signed-off-by: Vlastimil Babka --- mm/slub.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'mm/slub.c') diff --git a/mm/slub.c b/mm/slub.c index ecc44067625c..b81a4bba1b73 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -910,7 +910,7 @@ static void print_trailer(struct kmem_cache *s, struct slab *slab, u8 *p) if (slub_debug_orig_size(s)) off += sizeof(unsigned int); - off += kasan_metadata_size(s); + off += kasan_metadata_size(s, false); if (off != size_from_object(s)) /* Beginning of the filler is the free pointer */ @@ -1070,7 +1070,7 @@ static int check_pad_bytes(struct kmem_cache *s, struct slab *slab, u8 *p) off += sizeof(unsigned int); } - off += kasan_metadata_size(s); + off += kasan_metadata_size(s, false); if (size_from_object(s) == off) return 1; -- cgit v1.2.1 From 946fa0dbf2d8923a587f7348adf16563d59f1b3d Mon Sep 17 00:00:00 2001 From: Feng Tang Date: Fri, 21 Oct 2022 11:24:05 +0800 Subject: mm/slub: extend redzone check to extra allocated kmalloc space than requested kmalloc will round up the request size to a fixed size (mostly power of 2), so there could be a extra space than what is requested, whose size is the actual buffer size minus original request size. To better detect out of bound access or abuse of this space, add redzone sanity check for it. In current kernel, some kmalloc user already knows the existence of the space and utilizes it after calling 'ksize()' to know the real size of the allocated buffer. So we skip the sanity check for objects which have been called with ksize(), as treating them as legitimate users. Kees Cook is working on sanitizing all these user cases, by using kmalloc_size_roundup() to avoid ambiguous usages. And after this is done, this special handling for ksize() can be removed. In some cases, the free pointer could be saved inside the latter part of object data area, which may overlap the redzone part(for small sizes of kmalloc objects). As suggested by Hyeonggon Yoo, force the free pointer to be in meta data area when kmalloc redzone debug is enabled, to make all kmalloc objects covered by redzone check. Suggested-by: Vlastimil Babka Signed-off-by: Feng Tang Acked-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> Signed-off-by: Vlastimil Babka --- mm/slub.c | 50 +++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 45 insertions(+), 5 deletions(-) (limited to 'mm/slub.c') diff --git a/mm/slub.c b/mm/slub.c index b81a4bba1b73..5f3e34923065 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -829,6 +829,17 @@ static inline void set_orig_size(struct kmem_cache *s, if (!slub_debug_orig_size(s)) return; +#ifdef CONFIG_KASAN_GENERIC + /* + * KASAN could save its free meta data in object's data area at + * offset 0, if the size is larger than 'orig_size', it will + * overlap the data redzone in [orig_size+1, object_size], and + * the check should be skipped. + */ + if (kasan_metadata_size(s, true) > orig_size) + orig_size = s->object_size; +#endif + p += get_info_end(s); p += sizeof(struct track) * 2; @@ -848,6 +859,11 @@ static inline unsigned int get_orig_size(struct kmem_cache *s, void *object) return *(unsigned int *)p; } +void skip_orig_size_check(struct kmem_cache *s, const void *object) +{ + set_orig_size(s, (void *)object, s->object_size); +} + static void slab_bug(struct kmem_cache *s, char *fmt, ...) { struct va_format vaf; @@ -966,17 +982,28 @@ static __printf(3, 4) void slab_err(struct kmem_cache *s, struct slab *slab, static void init_object(struct kmem_cache *s, void *object, u8 val) { u8 *p = kasan_reset_tag(object); + unsigned int poison_size = s->object_size; - if (s->flags & SLAB_RED_ZONE) + if (s->flags & SLAB_RED_ZONE) { memset(p - s->red_left_pad, val, s->red_left_pad); + if (slub_debug_orig_size(s) && val == SLUB_RED_ACTIVE) { + /* + * Redzone the extra allocated space by kmalloc than + * requested, and the poison size will be limited to + * the original request size accordingly. + */ + poison_size = get_orig_size(s, object); + } + } + if (s->flags & __OBJECT_POISON) { - memset(p, POISON_FREE, s->object_size - 1); - p[s->object_size - 1] = POISON_END; + memset(p, POISON_FREE, poison_size - 1); + p[poison_size - 1] = POISON_END; } if (s->flags & SLAB_RED_ZONE) - memset(p + s->object_size, val, s->inuse - s->object_size); + memset(p + poison_size, val, s->inuse - poison_size); } static void restore_bytes(struct kmem_cache *s, char *message, u8 data, @@ -1120,6 +1147,7 @@ static int check_object(struct kmem_cache *s, struct slab *slab, { u8 *p = object; u8 *endobject = object + s->object_size; + unsigned int orig_size; if (s->flags & SLAB_RED_ZONE) { if (!check_bytes_and_report(s, slab, object, "Left Redzone", @@ -1129,6 +1157,17 @@ static int check_object(struct kmem_cache *s, struct slab *slab, if (!check_bytes_and_report(s, slab, object, "Right Redzone", endobject, val, s->inuse - s->object_size)) return 0; + + if (slub_debug_orig_size(s) && val == SLUB_RED_ACTIVE) { + orig_size = get_orig_size(s, object); + + if (s->object_size > orig_size && + !check_bytes_and_report(s, slab, object, + "kmalloc Redzone", p + orig_size, + val, s->object_size - orig_size)) { + return 0; + } + } } else { if ((s->flags & SLAB_POISON) && s->object_size < s->inuse) { check_bytes_and_report(s, slab, p, "Alignment padding", @@ -4206,7 +4245,8 @@ static int calculate_sizes(struct kmem_cache *s) */ s->inuse = size; - if ((flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)) || + if (slub_debug_orig_size(s) || + (flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)) || ((flags & SLAB_RED_ZONE) && s->object_size < sizeof(void *)) || s->ctor) { /* -- cgit v1.2.1