linux-kernel - Re: [PATCH v6 0/5] Allow guest access to EFI confidential computing secret area

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Date:   Fri, 7 Jan 2022 12:16:05 -0700
From:   Peter Gonda <pgonda@...gle.com>
To:     Borislav Petkov <bp@...e.de>
Cc:     "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        linux-efi@...r.kernel.org, Ashish Kalra <ashish.kalra@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrew Scull <ascull@...gle.com>,
        Dave Hansen <dave.hansen@...el.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@...ux.ibm.com>,
        Jim Cadden <jcadden@....com>,
        Daniele Buono <dbuono@...ux.vnet.ibm.com>,
        linux-coco@...ts.linux.dev, linux-security-module@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 0/5] Allow guest access to EFI confidential computing
 secret area

On Fri, Jan 7, 2022 at 4:59 AM Borislav Petkov <bp@...e.de> wrote:
>
> On Wed, Jan 05, 2022 at 08:07:04PM +0000, Dr. David Alan Gilbert wrote:
> > I thought I saw something in their patch series where they also had a
> > secret that got passed down from EFI?
>
> Probably. I've seen so many TDX patchsets so that I'm completely
> confused what is what.
>
> > As I remember they had it with an ioctl and something; but it felt to
> > me if it would be great if it was shared.
>
> I guess we could try to share
>
> https://lore.kernel.org/r/20211210154332.11526-28-brijesh.singh@amd.com
>
> for SNP and TDX.
>
> > I'd love to hear from those other cloud vendors; I've not been able to
> > find any detail on how their SEV(-ES) systems actually work.
>
> Same here.
>
> > However, this aims to be just a comms mechanism to pass that secret;
> > so it's pretty low down in the stack and is there for them to use -
> > hopefully it's general enough.
>
> Exactly!
>
> > (An interesting question is what exactly gets passed in this key and
> > what it means).
> >
> > All the contentious stuff I've seen seems to be further up the stack - like
> > who does the attestation and where they get the secrets and how they
> > know what a valid measurement looks like.
>
> It would be much much better if all the parties involved would sit down
> and decide on a common scheme so that implementation can be shared but
> getting everybody to agree is likely hard...

I saw a request for other cloud provider input here. A little
background for our SEV VMs in GCE we rely on our vTPM for attestation,
we do this because of SEV security properties quoting from AMD being
to protect guests from a benign but vulnerable hypervisor. So a
benign/compliant hypervisor's vTPM wouldn't lie to the guest. So we
added a few bits in the PCRs to allow users to see their SEV status in
vTPM quotes.

It would be very interesting to offer an attestation solution that
doesn't rely on our virtual TPM. But after reading through this cover
letter and the linked OVMF patches I am confused what's the high level
flow you are working towards? Are you loading in some OVMF using
LAUNCH_UPDATE_DATA, getting the measurement with LAUNCH_MEASURE, then
sending that to the customer who can then craft a "secret" (maybe say
SSH key) for injection with LAUNCH_SECRET? Thats sounds good but there
are a lot details left unattested there, how do you know you will boot
from the image loaded with the PSP into a known state? Do you have
some documentation I could read through to try and understand a little
more and apologies if I missed it.

>
> --
> Regards/Gruss,
>     Boris.
>
> SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg
>