linux-kernel - Re: [RFC PATCH 0/3] Allow access to confidential computing secret area

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Message-ID: <d6b991603d79cfbaf05c93f8b662860b865d861b.camel@linux.ibm.com>
Date:   Fri, 21 May 2021 09:03:23 -0700
From:   James Bottomley <jejb@...ux.ibm.com>
To:     Brijesh Singh <brijesh.singh@....com>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>
Cc:     Dov Murik <dovmurik@...ux.ibm.com>, linux-efi@...r.kernel.org,
        Tobin Feldman-Fitzthum <tobin@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Jim Cadden <jcadden@....com>,
        Hubertus Franke <frankeh@...ibm.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Laszlo Ersek <lersek@...hat.com>,
        Ashish Kalra <ashish.kalra@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/3] Allow access to confidential computing secret
 area

On Fri, 2021-05-21 at 10:56 -0500, Brijesh Singh wrote:
[...]
> In case of the SEV-SNP and TDX, the guest OS participates during the
> attestation flow; the driver working on the behalf of userspace and
> does not have access to the secret, so it cannot populate the file
> with the secrets in it.

OK, so for a simple encrypted VM using root on luks, how in SNP does
the boot loader obtain the disk passphrase?

In the non SNP case, it's already upstream: OVMF finds the secret page
and converts it to an EFI config table, which is passed into grub. 
It's starting to sound like we'll need a new grub module for SNP which
will do an active attestation and receive the passphrase over some
channel secure against the cloud provider.  Could you give us an
example of how you think this flow will work?

Thanks,

James