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Message-ID: <alpine.DEB.2.21.2001291640350.1546@www.lameter.com>
Date: Wed, 29 Jan 2020 16:43:30 +0000 (UTC)
From: Christopher Lameter <cl@...ux.com>
To: Kees Cook <keescook@...omium.org>
cc: Christian Borntraeger <borntraeger@...ibm.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>,
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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>,
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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 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.
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