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Message-ID: <202001300945.7D465B5F5@keescook>
Date: Thu, 30 Jan 2020 11:23:38 -0800
From: Kees Cook <keescook@...omium.org>
To: Christian Borntraeger <borntraeger@...ibm.com>
Cc: 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>,
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@...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@...r.kernel.org,
linux-arch@...r.kernel.org, netdev@...r.kernel.org,
kernel-hardening@...ts.openwall.com,
Vlastimil Babka <vbabka@...e.cz>, Michal Kubecek <mkubecek@...e.cz>
Subject: Re: [PATCH 09/38] usercopy: Mark kmalloc caches
as usercopy caches
On Wed, Jan 29, 2020 at 06:19:56PM +0100, Christian Borntraeger wrote:
> On 29.01.20 18:09, Christoph Hellwig wrote:
> > On Wed, Jan 29, 2020 at 06:07:14PM +0100, Christian Borntraeger wrote:
> >>> DMA can be done to NORMAL memory as well.
> >>
> >> Exactly.
> >> I think iucv uses GFP_DMA because z/VM needs those buffers to reside below 2GB (which is ZONA_DMA for s390).
> >
> > The normal way to allocate memory with addressing limits would be to
> > use dma_alloc_coherent and friends. Any chance to switch iucv over to
> > that? Or is there no device associated with it?
>
> There is not necessarily a device for that. It is a hypervisor interface (an
> instruction that is interpreted by z/VM). We do have the netiucv driver that
> creates a virtual nic, but there is also AF_IUCV which works without a device.
>
> But back to the original question: If we mark kmalloc caches as usercopy caches,
> we should do the same for DMA kmalloc caches. As outlined by Christoph, this has
> nothing to do with device DMA.
Hm, looks like it's allocated from the low 16MB. Seems like poor naming!
:) There seems to be a LOT of stuff using GFP_DMA, and it seems unlikely
those are all expecting low addresses?
Since this has only been a problem on s390, should just s390 gain the
weakening of the usercopy restriction? Something like:
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 1907cb2903c7..c5bbc141f20b 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1303,7 +1303,9 @@ 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,
+ IS_ENABLED(CONFIG_S390) ?
+ kmalloc_info[i].size : 0);
}
}
#endif
--
Kees Cook
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