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

[Richard Relph]

On 9/29/17 2:34 PM, Michael S. Tsirkin wrote:
> 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.

A BIOS "signed" by the CP doesn't meet the security requirement. It is 
code that is "unknown" to the GO.

The (legitimate) CP does NOT want to be in that position of trust. If 
they are, then some government somewhere is going to insist that they 
sign a BIOS that allows the government to spy on the GO's VMs, and steal 
secrets from it. Or some hacker admin will do it "for fun".

How often do large public CPs really change their BIOSes? My sense is 
that large public CPs prefer stability over "latest and greatest".

And, perhaps more importantly, if a CP are able to sell a "more secure" 
VM, one that justifies a higher price per vCPU hour, wouldn't that 
warrant some changes in the "insecure" model being used today?

Richard