From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58260) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bkArv-00079R-4Y for qemu-devel@nongnu.org; Wed, 14 Sep 2016 10:08:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bkArp-0005rb-Bm for qemu-devel@nongnu.org; Wed, 14 Sep 2016 10:08:54 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36826) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bkArp-0005rQ-3s for qemu-devel@nongnu.org; Wed, 14 Sep 2016 10:08:49 -0400 Date: Wed, 14 Sep 2016 11:08:45 -0300 From: Eduardo Habkost Message-ID: <20160914140845.GD24695@thinpad.lan.raisama.net> References: <147377800565.11859.4411044563640180545.stgit@brijesh-build-machine> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160914164859-mutt-send-email-mst@kernel.org> 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: "Michael S. Tsirkin" Cc: "Daniel P. Berrange" , Paolo Bonzini , Brijesh Singh , 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 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. I believe the whole point of SEV attestation and key management is to make "if attacker can executed code in hypervisor, encrypting memory is not useful" _not_ true, isn't it? Or are there known vulnerabilities that would allow a compromised hypervisor to decrypt memory even after successful encryption+attestation? -- Eduardo