From 49f2d2419d60a103752e5fbaf158cf8d07c0d884 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Mon, 1 Jun 2020 21:45:43 -0700 Subject: [PATCH] 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 Signed-off-by: Andrew Morton Acked-by: Christian Borntraeger Acked-by: Jiri Slaby Cc: Jann Horn Cc: Christoph Hellwig Cc: Christopher Lameter Cc: Julian Wiedmann Cc: Ursula Braun Cc: Alexander Viro Cc: David Windsor Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Andy Lutomirski Cc: "David S. Miller" Cc: Laura Abbott Cc: Mark Rutland Cc: "Martin K. Petersen" Cc: Paolo Bonzini Cc: Christoffer Dall Cc: Dave Kleikamp Cc: Jan Kara Cc: Luis de Bethencourt Cc: Marc Zyngier Cc: Rik van Riel Cc: Matthew Garrett Cc: Michal Kubecek Link: http://lkml.kernel.org/r/7d810f6d-8085-ea2f-7805-47ba3842dc50@suse.cz Signed-off-by: Linus Torvalds --- mm/slab_common.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/slab_common.c b/mm/slab_common.c index 23c7500eea7d..9e72ba224175 100644 --- 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 -- 2.39.5