Re: [PATCH] tpm: add backend for mssim

[James Bottomley <jejb@linux.ibm.com>]

On Mon, 2022-12-12 at 09:44 -0500, Stefan Berger wrote:
> 
> 
> 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?

I don't actually use virsh in my harness.  I'm mostly interested in the
running the kernel TPM selftests against the reference model.  But I
anticipate it wouldn't currently work because I don't believe virsh
triggers a S3 event which is why snapshot and migration doesn't always
work with PCI passthrough.

James