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Subject: Re: [PATCH 0/4] keys: Introduce a keys frontend for attestation
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From:   James Bottomley <James.Bottomley@HansenPartnership.com>
To:     Dionna Amalie Glaze <dionnaglaze@google.com>
Cc:     Dan Williams <dan.j.williams@intel.com>,
        Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@linux.intel.com>, dhowells@redhat.com,
        Brijesh Singh <brijesh.singh@amd.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Borislav Petkov <bp@alien8.de>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Samuel Ortiz <sameo@rivosinc.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-coco@lists.linux.dev, keyrings@vger.kernel.org,
        x86@kernel.org, linux-kernel@vger.kernel.org
Date:   Tue, 08 Aug 2023 17:46:04 -0400
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On Tue, 2023-08-08 at 13:04 -0700, Dionna Amalie Glaze wrote:
> > Trusting the vTPM is a one time thing.  Once trust in the TPM is
> > established, you don't need to be worried about replay and you can
> > just use standard TPM primitives for everything onward, even when
> > doing point in time runtime attestation.
> > 
> 
> It's a one time thing for who?

Well, in TLS-TPM it tends to be a one time thing per endpoint
regardless of number of connections.

>  It seems like you're still only looking at the 1. use case and not
> the 2. use case. Every different person establishing a connection
> with the service will need to independently establish trust in the
> TPM.

For an ephemeral TPM, the EK should be guaranteed to be random and
therefore non repeating, so there's not much need for the nonce to add
non-repeatability.  So, in theory, the vTPM/EK binding can be published
once and relied on even for multiple different tenant endpoints, sort
of like the EK cert for a physical TPM.

James