Re: [Qemu-devel] libvirt/QEMU/SEV interaction

[Michael S. Tsirkin]

On Wed, Sep 27, 2017 at 02:06:10PM -0500, Richard Relph wrote:
> Whether the "BIOS" is a "static shim" as Michael suggests, or a full BIOS,
> or even a BIOS+kernel+initrd is really not too significant. What is
> significant is that the GO has a basis for trusting all code that is
> imported in to their VM by the CP. And that NONE of the code provided by the
> CP is "unknown" and unauditable by the GO. If the CP has a way to inject
> code unknown to the GO in to the guest VM, the trust model is broken and
> both GO and CP suffer the consequences.

Absolutely.

> When the CP needs to update the BIOS image, they will have to inform the GO
> and allow the GO to establish trust in the CP's new BIOS image somehow.

This GO update on every BIOS change is imho is not a workable model. You
want something like checking the BIOS signature instead. And since
hardware is all hash based, you need the shim to do it in software.

-- 
MST