Re: [RFC PATCH v3 13/20] x86: DMA support for memory encryption

From: Michael S. Tsirkin
Date: Tue Nov 22 2016 - 15:41:42 EST

On Tue, Nov 22, 2016 at 04:41:37PM +0100, Borislav Petkov wrote:
> On Tue, Nov 22, 2016 at 05:22:38PM +0200, Michael S. Tsirkin wrote:
> > The issue is it's a (potential) security hole, not a slowdown.
> How? Because the bounce buffers will be unencrypted and someone might
> intercept them?

Or even modify them. Guests generally trust devices since they
assume they are under their control.

> > To disable unsecure things. If someone enables SEV one might have an
> > expectation of security. Might help push vendors to do the right thing
> > as a side effect.
> Ok, you're looking at the SEV-cloud-multiple-guests aspect. Right, that
> makes sense.
> I guess for SEV we should even flip the logic: disable such devices by
> default and an opt-in option to enable them and issue a big fat warning.
> I'd even want to let the guest users know that they're on a system which
> cannot give them encrypted DMA to some devices...
> --
> Regards/Gruss,
> Boris.
> Good mailing practices for 400: avoid top-posting and trim the reply.