From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42012) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bkBU8-0003Z5-3B for qemu-devel@nongnu.org; Wed, 14 Sep 2016 10:48:25 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bkBU3-0002I8-L4 for qemu-devel@nongnu.org; Wed, 14 Sep 2016 10:48:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52732) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bkBU3-0002Hz-DN for qemu-devel@nongnu.org; Wed, 14 Sep 2016 10:48:19 -0400 Date: Wed, 14 Sep 2016 17:48:17 +0300 From: "Michael S. Tsirkin" Message-ID: <20160914173830-mutt-send-email-mst@kernel.org> References: <147377810767.11859.4668503556528840901.stgit@brijesh-build-machine> <20160914052034-mutt-send-email-mst@kernel.org> <4f4370ee-bc29-3427-7e6e-a18d50c27ffc@redhat.com> <20160914155913-mutt-send-email-mst@kernel.org> <0fd3cbb9-9e46-9373-e989-acb45b56e8a9@redhat.com> <20160914132314.GR28399@redhat.com> <20160914163045-mutt-send-email-mst@kernel.org> <20160914133749.GT28399@redhat.com> <20160914164859-mutt-send-email-mst@kernel.org> <20160914141507.GU28399@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160914141507.GU28399@redhat.com> Subject: Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. Berrange" Cc: Paolo Bonzini , Brijesh Singh , ehabkost@redhat.com, crosthwaite.peter@gmail.com, p.fedin@samsung.com, qemu-devel@nongnu.org, armbru@redhat.com, lcapitulino@redhat.com, rth@twiddle.net On Wed, Sep 14, 2016 at 03:15:07PM +0100, Daniel P. Berrange wrote: > 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 You mean presentation claimed protection against leaks to a malicious active attacker within a hypervisor? I guess the presentation covers more than this patchset does then. And the disconnect would be with what the patchset cover letter says, not just with what I say. Clearly encrypting memory is not enough to protect against a malicious hypervisor. E.g. just running info cpus is enough to leak information from guest. > -- > |: 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 :|