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Date: Wed, 29 Jan 2020 16:43:30 +0000 (UTC)
From: Christopher Lameter <>
To: Kees Cook <>
cc: Christian Borntraeger <>, 
    Jiri Slaby <>, Julian Wiedmann <>, 
    Ursula Braun <>, 
    Alexander Viro <>,, 
    David Windsor <>, Pekka Enberg <>, 
    David Rientjes <>, Joonsoo Kim <>, 
    Andrew Morton <>,,, Linus Torvalds <>, 
    Andy Lutomirski <>, Christoph Hellwig <>, 
    "David S. Miller" <>, Laura Abbott <>, 
    Mark Rutland <>, 
    "Martin K. Petersen" <>, 
    Paolo Bonzini <>, 
    Christoffer Dall <>, 
    Dave Kleikamp <>, Jan Kara <>, 
    Luis de Bethencourt <>, 
    Marc Zyngier <>, Rik van Riel <>, 
    Matthew Garrett <>,,,,, Vlastimil Babka <>, 
    Michal Kubecek <>
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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