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

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Message-ID: <YdXq9t75aYLJfb69@zn.tnic>
Date:   Wed, 5 Jan 2022 20:01:10 +0100
From:   Borislav Petkov <bp@...e.de>
To:     "Dr. David Alan Gilbert" <dgilbert@...hat.com>
Cc:     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,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 0/5] Allow guest access to EFI confidential computing
 secret area

On Wed, Jan 05, 2022 at 11:43:25AM +0000, Dr. David Alan Gilbert wrote:
> There's more than one type of dance;

So Brijesh and I talked about this a bit yesterday. There's all kinds of
dances...

> this partially varies depending on the system (SEV/TDX etc)

By "SEV" I guess you mean pre-SNP because SNP attestation is reportedly
much better.

TDX I'm being told is not interested in something like that atm. I guess
they wanna do something different wrt attestation.

So what we're talking about here is pre-SNP attestation, AFAICT.

> and also depends on how you depend to boot your VM (separate kernel
> or VM disk). Also it's important to note that when the dance happens
> varies - in SEV and SEV-ES this happens before the guest executes any
> code. So at the end of the dance, the guest owner hands over that
> secret - but only then does the geust start booting;

Right.

> that secret has to go somewhere to be used by something later. For
> example, something might pull out that key and use it to decrypt a
> disk that then has other secrets on it (e.g. your ssh key).

That is the other example I heard about.

So, to sum up: this looks like part of a pre-SNP attestation flow, i.e.,
for SEV and SEV-ES guests.

Follow-up question: is this going to be used by other cloud vendors too?
Or am I gonna get another implementation of sharing secrets with a guest
which is just a little bit different but sender #2 can't use this one
because raisins?

Because that would not be good.

So, is this what cloud vendors using SEV/-ES guests would like to use
and what they all agree upon?

Thx.

-- 
Regards/Gruss,
    Boris.

SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg