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Re: [PATCH] tpm: add backend for mssim


From: Stefan Berger
Subject: Re: [PATCH] tpm: add backend for mssim
Date: Mon, 12 Dec 2022 09:44:25 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1



On 12/12/22 09:32, James Bottomley wrote:
On Mon, 2022-12-12 at 09:27 -0500, Stefan Berger wrote:


On 12/12/22 08:59, James Bottomley wrote:
On Mon, 2022-12-12 at 08:43 -0500, Stefan Berger wrote:


On 12/10/22 12:10, James Bottomley wrote:
The Microsoft Simulator (mssim) is the reference emulation
platform
for the TCG TPM 2.0 specification.

https://github.com/Microsoft/ms-tpm-20-ref.git

It exports a fairly simple network socket baset protocol on two

baset -> based.

sockets, one for command (default 2321) and one for control
(default 2322).  This patch adds a simple backend that can
speak the mssim protocol over the network.  It also allows the
host, and two ports to be specified on the qemu command line.
The benefits are twofold: firstly it gives us a backend that
actually speaks a standard TPM emulation protocol instead of
the linux specific TPM driver format of the current emulated
TPM backend and secondly, using the microsoft protocol, the end
point of the emulator can be anywhere on the network,
facilitating the cloud use case where a central TPM ervice can
be used over a control network.

The implementation does basic control commands like power
off/on, but doesn't implement cancellation or startup.  The
former because cancellation is pretty much useless on a fast
operating TPM emulator and the latter because this emulator is
designed to be used with OVMF which itself does TPM startup and
I wanted to validate that.

How did you implement VM suspend/resume and snapshotting support?

TPM2 doesn't need to.  The mssim follows the reference model which


You mean TPM2 doesn't need to resume at the point where the VM
resumes (I am not talking about ACPI resume but virsh save/restore)
after for example a host reboot?
What does this have to do with the mssim reference model and
TPM2_Shutdown protocol?

Running S3 suspend/resume before doing VM save/restore could fix a lot
of issue with passthrough PCI and when QEMU gets around to doing that a
TPM following the standard model should just work.  It's useful to have
a driver supporting this work.
Did you test it with virsh save / restore with the mssim TPM? Does it work? 
Does it work if you reboot the host in between?

   Stefan


James




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