On Wed, Sep 14, 2016 at 04:50:51PM +0300, Michael S. Tsirkin wrote: > On Wed, Sep 14, 2016 at 02:37:49PM +0100, Daniel P. Berrange wrote: > > On Wed, Sep 14, 2016 at 04:32:44PM +0300, Michael S. Tsirkin wrote: > > > On Wed, Sep 14, 2016 at 02:23:14PM +0100, Daniel P. Berrange wrote: > > > > On Wed, Sep 14, 2016 at 03:07:58PM +0200, Paolo Bonzini wrote: > > > > > > > > > > > > > > > On 14/09/2016 15:05, Michael S. Tsirkin wrote: > > > > > > I assumed that with debug on, memory is still encrypted but the > > > > > > hypervisor can break encryption, and as the cover letter states, the > > > > > > hypervisor is assumed benign. If true I don't see a need to > > > > > > give users more rope. > > > > > > > > > > The hypervisor is assumed benign but vulnerable. > > > > > > > > > > So, if somebody breaks the hypervisor, you would like to make it as > > > > > hard > > > > > as possible for the attacker to do evil stuff to the guests. If the > > > > > attacker can just ask the secure processor "decrypt some memory for > > > > > me", > > > > > then the encryption is effectively broken. > > > > > > > > So there's going to be a tradeoff here between use of SEV and use of > > > > certain other features. eg, it seems that if you're using SEV, then > > > > any concept of creating & analysing guest core dumps from the host > > > > is out. > > > > > > I don't see why - as long as we don't trigger dumps, there's no leak :) > > > > If the facility to trigger dumps is available, then the memory > > encryption feature of SEV is as useful as a chocolate teapot, > > as the would be attacker can simply trigger a dump > > If attacker can trigger things, IOW execute code in hypervisor, > then encrypting memory is not useful anyway.
The presentation at KVM forum claimed it *would* protect against this, and that things like core dump of unencrypted memory would not be permitted, so there's a disconnect between that preso and what you're saying. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|
