On Mon, 2016-07-25 at 16:29 -0700, Laura Abbott wrote: > 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. > That's fair. I have no objection to the check, but would like to see it documented, since it does look a little out of place. -- All Rights Reversed.
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