linux-kernel - Re: Linux guest kernel threat model for Confidential Computing

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Message-ID: <Y9KaoZKjyKD8aokf@work-vm>
Date:   Thu, 26 Jan 2023 15:22:09 +0000
From:   "Dr. David Alan Gilbert" <dgilbert@...hat.com>
To:     Richard Weinberger <richard.weinberger@...il.com>
Cc:     Daniel P. Berrangé <berrange@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Reshetova, Elena" <elena.reshetova@...el.com>,
        "Shishkin, Alexander" <alexander.shishkin@...el.com>,
        "Shutemov, Kirill" <kirill.shutemov@...el.com>,
        "Kuppuswamy, Sathyanarayanan" <sathyanarayanan.kuppuswamy@...el.com>,
        "Kleen, Andi" <andi.kleen@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "Wunner, Lukas" <lukas.wunner@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "Poimboe, Josh" <jpoimboe@...hat.com>,
        "aarcange@...hat.com" <aarcange@...hat.com>,
        Cfir Cohen <cfir@...gle.com>, Marc Orr <marcorr@...gle.com>,
        "jbachmann@...gle.com" <jbachmann@...gle.com>,
        "pgonda@...gle.com" <pgonda@...gle.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        James Morris <jmorris@...ei.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        "Lange, Jon" <jlange@...rosoft.com>,
        "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux guest kernel threat model for Confidential Computing

* Richard Weinberger (richard.weinberger@...il.com) wrote:
> On Thu, Jan 26, 2023 at 3:58 PM Dr. David Alan Gilbert
> <dgilbert@...hat.com> wrote:
> >
> > * Richard Weinberger (richard.weinberger@...il.com) wrote:
> > > On Wed, Jan 25, 2023 at 3:22 PM Daniel P. Berrangé <berrange@...hat.com> wrote:
> > > > Any virtual device exposed to the guest that can transfer potentially
> > > > sensitive data needs to have some form of guest controlled encryption
> > > > applied. For disks this is easy with FDE like LUKS, for NICs this is
> > > > already best practice for services by using TLS. Other devices may not
> > > > have good existing options for applying encryption.
> > >
> > > I disagree wrt. LUKS. The cryptography behind LUKS protects persistent data
> > > but not transport. If an attacker can observe all IO you better
> > > consult a cryptographer.
> > > LUKS has no concept of session keys or such, so the same disk sector will
> > > always get encrypted with the very same key/iv.
> >
> > Are you aware of anything that you'd use instead?
> 
> Well, I'd think towards iSCSI over TLS to protect the IO transport.

Yeh, that's not entirely crazy for VMs which tend to come off some
remote storage system.

> > Are you happy with dm-verity for protection against modification?
> 
> Like LUKS (actually dm-crypt) the crypto behind is designed to protect
> persistent data not transport.
> My fear is that an attacker who is able to observe IOs can do bad things.

Hmm, OK,  I'd assumed dm-crypt was OK since it's more hashlike and
unchanging.

Dave

-- 
Dr. David Alan Gilbert / dgilbert@...hat.com / Manchester, UK