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? :) -- All Rights Reversed.
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