On 1/31/20 1:03 PM, Jann Horn wrote: > 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. So, let's do that? ----8<---- >From d5190e4e871689a530da3c3fd327be45a88f006a Mon Sep 17 00:00:00 2001 From: Vlastimil Babka <vbabka@xxxxxxx> Date: Tue, 7 Apr 2020 09:58:00 +0200 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@xxxxxxx/ [3] https://lore.kernel.org/kernel-hardening/CAG48ez1a4waGk9kB0WLaSbs4muSoK0AYAVk8=XYaKj4_+6e6Hg@xxxxxxxxxxxxxx/ Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> --- 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 5282f881d2f5..ae9486160594 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 -- 2.26.0
