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Message-ID: <7d810f6d-8085-ea2f-7805-47ba3842dc50@suse.cz>
Date: Tue, 7 Apr 2020 10:00:10 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Jann Horn <jannh@...gle.com>, Kees Cook <keescook@...omium.org>
Cc: Christian Borntraeger <borntraeger@...ibm.com>,
Christoph Hellwig <hch@...radead.org>, Christopher Lameter <cl@...ux.com>,
Jiri Slaby <jslaby@...e.cz>, Julian Wiedmann <jwi@...ux.ibm.com>,
Ursula Braun <ubraun@...ux.ibm.com>, Alexander Viro
<viro@...iv.linux.org.uk>, kernel list <linux-kernel@...r.kernel.org>,
David Windsor <dave@...lcore.net>, Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>,
Andrew Morton <akpm@...ux-foundation.org>, Linux-MM <linux-mm@...ck.org>,
linux-xfs@...r.kernel.org, Linus Torvalds <torvalds@...ux-foundation.org>,
Andy Lutomirski <luto@...nel.org>, "David S. Miller" <davem@...emloft.net>,
Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>,
"Martin K. Petersen" <martin.petersen@...cle.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Christoffer Dall <christoffer.dall@...aro.org>,
Dave Kleikamp <dave.kleikamp@...cle.com>, Jan Kara <jack@...e.cz>,
Luis de Bethencourt <luisbg@...nel.org>, Marc Zyngier
<marc.zyngier@....com>, Rik van Riel <riel@...hat.com>,
Matthew Garrett <mjg59@...gle.com>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
linux-arch <linux-arch@...r.kernel.org>,
Network Development <netdev@...r.kernel.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Michal Kubecek <mkubecek@...e.cz>
Subject: Re: [PATCH 09/38] usercopy: Mark kmalloc caches as
usercopy caches
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@...e.cz>
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@suse.cz/
[3] https://lore.kernel.org/kernel-hardening/CAG48ez1a4waGk9kB0WLaSbs4muSoK0AYAVk8=XYaKj4_+6e6Hg@mail.gmail.com/
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
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
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