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

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Message-ID: <YKuXI9TUBa3sjY3e@work-vm>
Date:   Mon, 24 May 2021 13:08:03 +0100
From:   "Dr. David Alan Gilbert" <dgilbert@...hat.com>
To:     Andi Kleen <ak@...ux.intel.com>, Dov Murik <dovmurik@...ux.ibm.com>
Cc:     Brijesh Singh <brijesh.singh@....com>, linux-efi@...r.kernel.org,
        Tobin Feldman-Fitzthum <tobin@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Jim Cadden <jcadden@....com>,
        James Bottomley <jejb@...ux.ibm.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,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [RFC PATCH 0/3] Allow access to confidential computing secret
 area

* Andi Kleen (ak@...ux.intel.com) wrote:
> 
> > The SEV-SNP attestation approach is very similar to what Andi described
> > for the TDX. However, in the case of legacy SEV and ES, the attestation
> > verification is performed before the guest is booted. In this case, the
> > hyervisor puts the secret provided by the guest owner (after the
> > attestation) at a fixed location. Dov's driver is simply reading that
> > fixed location and making it available through the simple text file.
> 
> That's the same as our SVKL model.
> 
> The (not yet posted) driver is here:
> 
> https://github.com/intel/tdx/commit/62c2d9fae275d5bf50f869e8cfb71d2ca1f71363
> 

Is there any way we could merge these two so that the TDX/SVKL would
look similar to SEV/ES to userspace?  If we needed some initrd glue here
for luks it would be great if we could have one piece of glue.
[I'm not sure if the numbering/naming of the secrets, and their format
are defined in the same way]

> We opted to use ioctls, with the idea that it should be just read and
> cleared once to not let the secret lying around. Typically you would just
> use it to set up dmcrypt or similar once. I think read-and-clear with
> explicit operations is a better model than some virtual file because of the
> security properties.

Do you think the ioctl is preferable to read+ftruncate/unlink ?
And if it was an ioctl, again could we get some standardisation here -
i.e.
maybe a /dev/confguest with a CONF_COMP_GET_KEY etc ?

Dave

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