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

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Message-ID: <20161122224005-mutt-send-email-mst@kernel.org>
Date:   Tue, 22 Nov 2016 22:41:30 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Tom Lendacky <thomas.lendacky@....com>, linux-arch@...r.kernel.org,
        linux-efi@...r.kernel.org, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Rik van Riel <riel@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v3 13/20] x86: DMA support for memory encryption

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.