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Date:   Tue, 8 Aug 2023 09:43:14 -0700
From:   Dan Williams <dan.j.williams@intel.com>
To:     Dionna Amalie Glaze <dionnaglaze@google.com>,
        Dan Williams <dan.j.williams@intel.com>
CC:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
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        <dhowells@redhat.com>, Brijesh Singh <brijesh.singh@amd.com>,
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Subject: Re: [PATCH 0/4] keys: Introduce a keys frontend for attestation
 reports
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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
> 
> 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
> 
> This posits the existence of such an advanced user, but high security
> applications also have users with high expectations. I want the option
> to be open to empower more users to have access to provable workload
> provenance, not just the VM owners that are unlocking resources.

I do not see sysfs precluding a use case like that. If the kernel can
call out to userspace for TLS connection setup [1], then advanced user
can call out to a daemon for workload provenance setup. Recall that TDX
will round trip through the quoting enclave for these reports and,
without measuring, that seems to have the potential to dominate the
setup time vs the communication to ask a daemon to convey a report.

[1]: https://lore.kernel.org/all/168174169259.9520.1911007910797225963.stgit@91.116.238.104.host.secureserver.net/