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From:   Christopher Lameter <cl@linux.com>
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Subject: Re: [kernel-hardening] [PATCH 09/38] usercopy: Mark kmalloc caches
 as usercopy caches
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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.