[PATCH 5.6 047/161] usercopy: mark dma-kmalloc caches as usercopy caches

[Greg Kroah-Hartman]

From: Vlastimil Babka <vbabka@xxxxxxx>

commit 49f2d2419d60a103752e5fbaf158cf8d07c0d884 upstream.

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@xxxxxxx/
[3] https://lore.kernel.org/kernel-hardening/CAG48ez1a4waGk9kB0WLaSbs4muSoK0AYAVk8=XYaKj4_+6e6Hg@xxxxxxxxxxxxxx/

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Acked-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Acked-by: Jiri Slaby <jslaby@xxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Christopher Lameter <cl@xxxxxxxxx>
Cc: Julian Wiedmann <jwi@xxxxxxxxxxxxx>
Cc: Ursula Braun <ubraun@xxxxxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: David Windsor <dave@xxxxxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Laura Abbott <labbott@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
Cc: Dave Kleikamp <dave.kleikamp@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Luis de Bethencourt <luisbg@xxxxxxxxxx>
Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Matthew Garrett <mjg59@xxxxxxxxxx>
Cc: Michal Kubecek <mkubecek@xxxxxxx>
Link: http://lkml.kernel.org/r/7d810f6d-8085-ea2f-7805-47ba3842dc50@xxxxxxx
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 mm/slab_common.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1303,7 +1303,8 @@ void __init create_kmalloc_caches(slab_f
 			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