From: Vlastimil Babka <vbabka@xxxxxxx> Subject: 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@xxxxxxx/ [3] https://lore.kernel.org/kernel-hardening/CAG48ez1a4waGk9kB0WLaSbs4muSoK0AYAVk8=XYaKj4_+6e6Hg@xxxxxxxxxxxxxx/ Link: http://lkml.kernel.org/r/7d810f6d-8085-ea2f-7805-47ba3842dc50@xxxxxxx Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> 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: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> 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> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/slab_common.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/mm/slab_common.c~usercopy-mark-dma-kmalloc-caches-as-usercopy-caches +++ a/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 _
