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Date: Wed, 29 Jan 2020 18:07:14 +0100
From: Christian Borntraeger <borntraeger@...ibm.com>
To: Christopher Lameter <cl@...ux.com>, Kees Cook <keescook@...omium.org>
Cc: 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>,
Christoph Hellwig <hch@...radead.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 29.01.20 17:43, Christopher Lameter wrote:
> On Tue, 28 Jan 2020, Kees Cook wrote:
>
>>> On the other hand not marking the DMA caches still seems questionable.
>>
>> My understanding is that exposing DMA memory to userspace copies can
>> lead to unexpected results, especially for misbehaving hardware, so I'm
>> not convinced this is a generically bad hardening choice.
>
> "DMA" memory (and thus DMA caches) have nothing to do with DMA. Its a
> legacy term. "DMA Memory" is memory limited to a certain
> physical address boundary (old restrictions on certain devices only
> supporting a limited number of address bits).
>
> 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).
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