[SRU][F][PATCH 1/1] usercopy: mark dma-kmalloc caches as usercopy caches

frank.heimes at canonical.com frank.heimes at canonical.com
Tue Oct 5 06:32:20 UTC 2021

From: Vlastimil Babka <vbabka at suse.cz>

BugLink: https://bugs.launchpad.net/bugs/1913442

Upstream commit : 49f2d2419d60a103752e5fbaf158cf8d07c0d884

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 at suse.cz>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Acked-by: Christian Borntraeger <borntraeger at de.ibm.com>
Acked-by: Jiri Slaby <jslaby at suse.cz>
Cc: Jann Horn <jannh at google.com>
Cc: Christoph Hellwig <hch at infradead.org>
Cc: Christopher Lameter <cl at linux.com>
Cc: Julian Wiedmann <jwi at linux.ibm.com>
Cc: Ursula Braun <ubraun at linux.ibm.com>
Cc: Alexander Viro <viro at zeniv.linux.org.uk>
Cc: David Windsor <dave at nullcore.net>
Cc: Pekka Enberg <penberg at kernel.org>
Cc: David Rientjes <rientjes at google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim at lge.com>
Cc: Andy Lutomirski <luto at kernel.org>
Cc: "David S. Miller" <davem at davemloft.net>
Cc: Laura Abbott <labbott at redhat.com>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: "Martin K. Petersen" <martin.petersen at oracle.com>
Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Christoffer Dall <christoffer.dall at linaro.org>
Cc: Dave Kleikamp <dave.kleikamp at oracle.com>
Cc: Jan Kara <jack at suse.cz>
Cc: Luis de Bethencourt <luisbg at kernel.org>
Cc: Marc Zyngier <marc.zyngier at arm.com>
Cc: Rik van Riel <riel at surriel.com>
Cc: Matthew Garrett <mjg59 at google.com>
Cc: Michal Kubecek <mkubecek at suse.cz>
Link: http://lkml.kernel.org/r/7d810f6d-8085-ea2f-7805-47ba3842dc50@suse.cz
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
(backported from commit 49f2d2419d60a103752e5fbaf158cf8d07c0d884)
Signed-off-by: Frank Heimes <frank.heimes at canonical.com>
 mm/slab_common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 8c1ffbf7de45..76433e2187d0 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1296,7 +1296,7 @@ void __init create_kmalloc_caches(slab_flags_t flags)
 			kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache(
-				n, size, SLAB_CACHE_DMA | flags, 0, 0);
+				n, size, SLAB_CACHE_DMA | flags, 0, kmalloc_info[i].size);

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