Messages in this thread Patch in this message | | | From | Laura Abbott <> | Subject | Re: [PATCH v4 12/12] mm: SLUB hardened usercopy support | Date | Mon, 25 Jul 2016 12:16:24 -0700 |
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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@chromium.org> > Tested-by: Michael Ellerman <mpe@ellerman.id.au> > --- > 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; With that, you can add
Reviwed-by: Laura Abbott <labbott@redhat.com>
> static size_t __ksize(const void *object) > { > struct page *page; >
Thanks, Laura
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