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

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Message-ID: <Y9KfvyjFmY3gN170@redhat.com>
Date:   Thu, 26 Jan 2023 15:43:59 +0000
From:   Daniel P. Berrangé <berrange@...hat.com>
To:     Richard Weinberger <richard.weinberger@...il.com>
Cc:     "Dr. David Alan Gilbert" <dgilbert@...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

On Thu, Jan 26, 2023 at 03:23:34PM +0100, Richard Weinberger 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.

Yes, you're right, all the FDE cipher modes are susceptible to
time based analysis of I/O, so very far from ideal. You'll get
protection for your historically written confidential data at the
time a VM host is first compromised, but if (as) they retain long
term access to the host, confidentiality is increasingly undermined
the longer they can observe the ongoing I/O.

With regards,
Daniel
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