On Mon, Jul 25, 2016 at 12:16 PM, Laura Abbott <labbott@xxxxxxxxxx> 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; > > With that, you can add > > Reviwed-by: Laura Abbott <labbott@xxxxxxxxxx> Cool, I'll add that. Should I add your reviewed-by for this patch only or for the whole series? Thanks! -Kees > >> static size_t __ksize(const void *object) >> { >> struct page *page; >> > > Thanks, > Laura -- Kees Cook Chrome OS & Brillo Security -- 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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