On Fri, Sep 29, 2017 at 02:48:45PM -0500, Richard Relph wrote: > 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". It is hard to generalize, but from a RHEL POV, we typically do major updates of the virt stack every ~6 months, and these will include BIOS updates. So if a cloud vendor is following the RHEL update stream actively that's the kind of cadence you'd expect. The gotcha would come if there were out-of-band security updates for BIOS which caused it to be updated before the 6 month window. Fortunately I've not see these happen often, so I don't think its a fatal problem. IOW, I tend to agree with you that this is not really a blocking problem to the use of SEV in cloud. > 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? Yes. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
