Re: Interactive launch over QMP socket?

[Daniel P . Berrangé]

On Mon, Feb 22, 2021 at 12:40:07PM +0100, Kevin Wolf wrote:
> Am 10.02.2021 um 19:01 hat Connor Kuehl geschrieben:
> > Hello,
> > 
> > Does QEMU have an internal API which would allow VM construction to wait at
> > a *very specific point* until specific data/QMP message(s) are supplied via
> > the QMP socket?
> > 
> > For some additional context: QEMU supports launching AMD SEV-protected
> > guests; in short: encrypted virtual machines. Guest owners may participate
> > in attestation to cryptographically verify their assumptions about the
> > guest's initial state, the host's platform, and the host platform owner's
> > identity. If the guest owner is satisfied with the attestation process, a
> > secret can be safely injected into the guest's address space over a secure
> > channel.
> > 
> > Attestation is an unavoidably interactive process.
> > 
> > It appears that QEMU already exposes most of the API required to perform
> > this attestation remotely with a guest owner over QMP, with only one
> > exception: starting the attestation session. It looks like the session
> > components (policy, session-file, and dh-cert-file) are supplied via command
> > line arguments to QEMU and don't have a message type in the QMP spec:
> > 
> >     -object 
> > sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=1,policy=0x1,session-file=blah.session,dh-cert-file=guest_owner.cert
> > 
> > I would like to add a message type to QMP which allows guest owners to
> > supply this data over a socket and _not_ require these components a priori
> > via command line arguments.
> 
> I don't think you need a new QMP command for this. If you would use
> -object on the command line, you can use QMP object-add at runtime.

If the object were standalone that'd true, but 'sev-guest' object you
create needs to be given to the '-machine' arg's 'memory-encryption'
parameter. So there's a dependancy that means 'sev-guest' can only
be used with -object in reality and not QMP object-add.

This will eventually be solved when we make it possible to fully
configure QEMU exclusively via QMP.

Regards,
Daniel
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