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Message-ID: <202004201043.538A7B3F2@keescook>
Date: Mon, 20 Apr 2020 10:43:37 -0700
From: Kees Cook <keescook@...omium.org>
To: Jiri Slaby <jslaby@...e.cz>
Cc: Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
Christoph Hellwig <hch@...radead.org>,
Christopher Lameter <cl@...ux.com>,
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 Mon, Apr 20, 2020 at 09:53:20AM +0200, Jiri Slaby wrote:
> On 07. 04. 20, 10:00, Vlastimil Babka wrote:
> > 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>
>
> Friendly ping.
>
> Acked-by: Jiri Slaby <jslaby@...e.cz>
Should this go via -mm?
-Kees
>
> > ---
> > 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
> >
>
> thanks,
> --
> js
> suse labs
--
Kees Cook
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