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Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command |
Date: |
Wed, 14 Sep 2016 18:17:51 +0300 |
On Wed, Sep 14, 2016 at 11:08:45AM -0300, Eduardo Habkost 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.
>
> 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?
That would be an aggressive claim. Not the one the cover letter is making.
> Or are there known vulnerabilities that would allow a compromised
> hypervisor to decrypt memory even after successful
> encryption+attestation?
> --
> Eduardo
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, (continued)
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Paolo Bonzini, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Michael S. Tsirkin, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Paolo Bonzini, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Daniel P. Berrange, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Michael S. Tsirkin, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Daniel P. Berrange, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Michael S. Tsirkin, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Eduardo Habkost, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Paolo Bonzini, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Michael S. Tsirkin, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Daniel P. Berrange, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Michael S. Tsirkin, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Daniel P. Berrange, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Michael S. Tsirkin, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Eduardo Habkost, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Michael S. Tsirkin, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Eduardo Habkost, 2016/09/15
- Re: [Qemu-devel] [PATCH v2] virtio_pci: Limit DMA mask to 44 bits for legacy virtio devices, Michael S. Tsirkin, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Brijesh Singh, 2016/09/14
- Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command, Michael S. Tsirkin, 2016/09/14