On 07.04.20 10:00, Vlastimil Babka wrote: > 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> Acked-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> > --- > 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 >
