linux-kernel - Re: [PATCH 0/4] keys: Introduce a keys frontend for attestation reports

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Date:   Tue, 08 Aug 2023 14:16:04 -0400
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Dionna Amalie Glaze <dionnaglaze@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>, dhowells@...hat.com,
        Brijesh Singh <brijesh.singh@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Borislav Petkov <bp@...en8.de>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Samuel Ortiz <sameo@...osinc.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-coco@...ts.linux.dev, keyrings@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] keys: Introduce a keys frontend for attestation
 reports

On Tue, 2023-08-08 at 09:07 -0700, Dionna Amalie Glaze wrote:
> > 
> > At least that was not the level of concurrency I was worried about.
> > The sysfs approach makes it so that concurrency problem of
> > option-writing vs report-reading is pushed to userspace.
> > 
> 
> The reason I would advocate against making attestation report
> collection single-threaded in user space at a machine level is that
> there are new schemes of attested connections that may become the
> basis of server handshakes. I think folks are mainly looking at this
> from the use case of
> 
> 1. workload will do large amounts of work on behalf of the VM owner,
> provided it gets a sealing key released by the VM owner once on boot
> after proving its code identity

Right, that's the case for boot time attestation.

> however I'm thinking of the case of a more user-centric use case that
> enables service users to challenge for proof of workload identity
> 
> 2. workload is a server that accepts incoming connections that
> include a hardware attestation challenge. It generates an attestation
> report that includes the challenge as part of the connection
> handshake

Isn't this more runtime attestation?  In which case you wouldn't use
the boot report.  I assume someone somewhere is hacking the TPM-TLS
protocol to also do RTMRs, but it strikes me we could just use a vTPM
and the existing protocols.

Even if you don't do anything as complex as TPM-TLS (and continuing
runtime attestation), you can still make TLS conditioned on a private
key released after a successful boot time attestation.  Since the boot
evidence never changes, there's not much point doing it on each
connection, so relying on a private key conditioned on boot evidence is
just as good.

James