On 07/25/2016 02:42 PM, Rik van Riel wrote:
On Mon, 2016-07-25 at 12:16 -0700, Laura Abbott wrote:On 07/20/2016 01:27 PM, Kees Cook wrote:Under CONFIG_HARDENED_USERCOPY, this adds object size checking to the SLUB allocator to catch any copies that may span objects. Includes a redzone handling fix discovered by Michael Ellerman. Based on code from PaX and grsecurity. Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> Tested-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> --- init/Kconfig | 1 + mm/slub.c | 36 ++++++++++++++++++++++++++++++++++++ 2 files changed, 37 insertions(+) diff --git a/init/Kconfig b/init/Kconfig index 798c2020ee7c..1c4711819dfd 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1765,6 +1765,7 @@ config SLAB config SLUB bool "SLUB (Unqueued Allocator)" + select HAVE_HARDENED_USERCOPY_ALLOCATOR help SLUB is a slab allocator that minimizes cache line usage instead of managing queues of cached objects (SLAB approach). diff --git a/mm/slub.c b/mm/slub.c index 825ff4505336..7dee3d9a5843 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3614,6 +3614,42 @@ void *__kmalloc_node(size_t size, gfp_t flags, int node) EXPORT_SYMBOL(__kmalloc_node); #endif +#ifdef CONFIG_HARDENED_USERCOPY +/* + * Rejects objects that are incorrectly sized. + * + * Returns NULL if check passes, otherwise const char * to name of cache + * to indicate an error. + */ +const char *__check_heap_object(const void *ptr, unsigned long n, + struct page *page) +{ + struct kmem_cache *s; + unsigned long offset; + size_t object_size; + + /* Find object and usable object size. */ + s = page->slab_cache; + object_size = slab_ksize(s); + + /* Find offset within object. */ + offset = (ptr - page_address(page)) % s->size; + + /* Adjust for redzone and reject if within the redzone. */ + if (kmem_cache_debug(s) && s->flags & SLAB_RED_ZONE) { + if (offset < s->red_left_pad) + return s->name; + offset -= s->red_left_pad; + } + + /* Allow address range falling entirely within object size. */ + if (offset <= object_size && n <= object_size - offset) + return NULL; + + return s->name; +} +#endif /* CONFIG_HARDENED_USERCOPY */ +I compared this against what check_valid_pointer does for SLUB_DEBUG checking. I was hoping we could utilize that function to avoid duplication but a) __check_heap_object needs to allow accesses anywhere in the object, not just the beginning b) accessing page->objects is racy without the addition of locking in SLUB_DEBUG. Still, the ptr < page_address(page) check from __check_heap_object would be good to add to avoid generating garbage large offsets and trying to infer C math. diff --git a/mm/slub.c b/mm/slub.c index 7dee3d9..5370e4f 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3632,6 +3632,9 @@ const char *__check_heap_object(const void *ptr, unsigned long n, s = page->slab_cache; object_size = slab_ksize(s); + if (ptr < page_address(page)) + return s->name; + /* Find offset within object. */ offset = (ptr - page_address(page)) % s->size;I don't get it, isn't that already guaranteed because we look for the page that ptr is in, before __check_heap_object is called? Specifically, in patch 3/12: + page = virt_to_head_page(ptr); + + /* Check slab allocator for flags and size. */ + if (PageSlab(page)) + return __check_heap_object(ptr, n, page); How can that generate a ptr that is not inside the page? What am I overlooking? And, should it be in the changelog or a comment? :)
I ran into the subtraction issue when the vmalloc detection wasn't working on ARM64, somehow virt_to_head_page turned into a page that happened to have PageSlab set. I agree if everything is working properly this is redundant but given the type of feature this is, a little bit of redundancy against a system running off into the weeds or bad patches might be warranted. I'm not super attached to the check if other maintainers think it is redundant. Updating the __check_heap_object header comment with a note of what we are assuming could work Thanks, Laura -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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