On Mon, 2019-08-19 at 17:06 +0300, Andrey Ryabinin wrote: > > On 8/19/19 4:34 PM, Will Deacon wrote: > > On Mon, Aug 19, 2019 at 02:23:48PM +0100, Mark Rutland wrote: > >> On Mon, Aug 19, 2019 at 01:56:26PM +0100, Will Deacon wrote: > >>> On Mon, Aug 19, 2019 at 07:44:20PM +0800, Walter Wu wrote: > >>>> __arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address, > >>>> but it will modify pointer tag into 0xff, so there is a false positive. > >>>> > >>>> When enable tag-based kasan, phys_to_virt() function need to rewrite > >>>> its original pointer tag in order to avoid kasan report an incorrect > >>>> memory corruption. > >>> > >>> Hmm. Which tree did you see this on? We've recently queued a load of fixes > >>> in this area, but I /thought/ they were only needed after the support for > >>> 52-bit virtual addressing in the kernel. > >> > >> I'm seeing similar issues in the virtio blk code (splat below), atop of > >> the arm64 for-next/core branch. I think this is a latent issue, and > >> people are only just starting to test with KASAN_SW_TAGS. > >> > >> It looks like the virtio blk code will round-trip a SLUB-allocated pointer > >> from > >> virt->page->virt, losing the per-object tag in the process. > >> > >> Our page_to_virt() seems to get a per-page tag, but this only makes > >> sense if you're dealing with the page allocator, rather than something > >> like SLUB which carves a page into smaller objects giving each object a > >> distinct tag. > >> > >> Any round-trip of a pointer from SLUB is going to lose the per-object > >> tag. > > > > Urgh, I wonder how this is supposed to work? > > > > We supposed to ignore pointers with 0xff tags. We do ignore them when memory > access checked, > but not in kfree() path. > This untested patch should fix the issue: > > > > --- > mm/kasan/common.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > index 895dc5e2b3d5..0a81cc328049 100644 > --- a/mm/kasan/common.c > +++ b/mm/kasan/common.c > @@ -407,7 +407,7 @@ static inline bool shadow_invalid(u8 tag, s8 shadow_byte) > return shadow_byte < 0 || > shadow_byte >= KASAN_SHADOW_SCALE_SIZE; > else > - return tag != (u8)shadow_byte; > + return (tag != KASAN_TAG_KERNEL) && (tag != (u8)shadow_byte); > } > > static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
Hi, Andrey, Does it miss the double-free case after ignore pointer tag 0xff ? and please help review my another patch about memory corruption identification. Thanks your respondence Walter
