usercopy: mark dma-kmalloc caches as usercopy caches

We have seen a "usercopy: Kernel memory overwrite attempt detected to
SLUB object 'dma-kmalloc-1 k' (offset 0, size 11)!" error on s390x, as
IUCV uses kmalloc() with __GFP_DMA because of memory address
restrictions.  The issue has been discussed [2] and it has been noted
that if all the kmalloc caches are marked as usercopy, there's little
reason not to mark dma-kmalloc caches too.  The 'dma' part merely means
that __GFP_DMA is used to restrict memory address range.

As Jann Horn put it [3]:
 "I think dma-kmalloc slabs should be handled the same way as normal
  kmalloc slabs. When a dma-kmalloc allocation is freshly created, it is
  just normal kernel memory - even if it might later be used for DMA -,
  and it should be perfectly fine to copy_from_user() into such
  allocations at that point, and to copy_to_user() out of them at the
  end. If you look at the places where such allocations are created, you
  can see things like kmemdup(), memcpy() and so on - all normal
  operations that shouldn't conceptually be different from usercopy in
  any relevant way."

Thus this patch marks the dma-kmalloc-* caches as usercopy.

[1] https://bugzilla.suse.com/show_bug.cgi?id=1156053
[2] https://lore.kernel.org/kernel-hardening/bfca96db-bbd0-d958-7732-76e36c667c68@suse.cz/
[3] https://lore.kernel.org/kernel-hardening/CAG48ez1a4waGk9kB0WLaSbs4muSoK0AYAVk8=XYaKj4_+6e6Hg@mail.gmail.com/

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Jiri Slaby <jslaby@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Christopher Lameter <cl@linux.com>
Cc: Julian Wiedmann <jwi@linux.ibm.com>
Cc: Ursula Braun <ubraun@linux.ibm.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: David Windsor <dave@nullcore.net>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Christoffer Dall <christoffer.dall@linaro.org>
Cc: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Luis de Bethencourt <luisbg@kernel.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Matthew Garrett <mjg59@google.com>
Cc: Michal Kubecek <mkubecek@suse.cz>
Link: http://lkml.kernel.org/r/7d810f6d-8085-ea2f-7805-47ba3842dc50@suse.cz
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 23c7500eea7d9197fa41b5d3ace65098aa7664b0..9e72ba2241750c4a8b8c32d84c9f9a1a79e4fb0e 100644 (file)
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1303,7 +1303,8 @@ void __init create_kmalloc_caches(slab_flags_t flags)
                        kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache(
                                kmalloc_info[i].name[KMALLOC_DMA],
                                kmalloc_info[i].size,
-                               SLAB_CACHE_DMA | flags, 0, 0);
+                               SLAB_CACHE_DMA | flags, 0,
+                               kmalloc_info[i].size);
                }
        }
 #endif