* Re: SEV guest attestation
2021-11-25 7:14 ` Sergio Lopez
@ 2021-11-25 12:44 ` Dov Murik
2021-11-25 13:42 ` Daniel P. Berrangé
2021-11-25 15:11 ` Sergio Lopez
2021-11-25 13:20 ` Dr. David Alan Gilbert
` (2 subsequent siblings)
3 siblings, 2 replies; 26+ messages in thread
From: Dov Murik @ 2021-11-25 12:44 UTC (permalink / raw)
To: Sergio Lopez, Dr. David Alan Gilbert, Tyler Fanelli
Cc: Daniel P. Berrangé, afrosi, James Bottomley, qemu-devel,
Dov Murik, Hubertus Franke, Tobin Feldman-Fitzthum, Jim Cadden,
dinechin, John Ferlan
[+cc jejb, tobin, jim, hubertus]
On 25/11/2021 9:14, Sergio Lopez wrote:
> On Wed, Nov 24, 2021 at 06:29:07PM +0000, Dr. David Alan Gilbert wrote:
>> * Daniel P. Berrangé (berrange@redhat.com) wrote:
>>> On Wed, Nov 24, 2021 at 11:34:16AM -0500, Tyler Fanelli wrote:
>>>> Hi,
>>>>
>>>> We recently discussed a way for remote SEV guest attestation through QEMU.
>>>> My initial approach was to get data needed for attestation through different
>>>> QMP commands (all of which are already available, so no changes required
>>>> there), deriving hashes and certificate data; and collecting all of this
>>>> into a new QMP struct (SevLaunchStart, which would include the VM's policy,
>>>> secret, and GPA) which would need to be upstreamed into QEMU. Once this is
>>>> provided, QEMU would then need to have support for attestation before a VM
>>>> is started. Upon speaking to Dave about this proposal, he mentioned that
>>>> this may not be the best approach, as some situations would render the
>>>> attestation unavailable, such as the instance where a VM is running in a
>>>> cloud, and a guest owner would like to perform attestation via QMP (a likely
>>>> scenario), yet a cloud provider cannot simply let anyone pass arbitrary QMP
>>>> commands, as this could be an issue.
>>>
>>> As a general point, QMP is a low level QEMU implementation detail,
>>> which is generally expected to be consumed exclusively on the host
>>> by a privileged mgmt layer, which will in turn expose its own higher
>>> level APIs to users or other apps. I would not expect to see QMP
>>> exposed to anything outside of the privileged host layer.
>>>
>>> We also use the QAPI protocol for QEMU guest agent commmunication,
>>> however, that is a distinct service from QMP on the host. It shares
>>> most infra with QMP but has a completely diffent command set. On the
>>> host it is not consumed inside QEMU, but instead consumed by a
>>> mgmt app like libvirt.
>>>
>>>> So I ask, does anyone involved in QEMU's SEV implementation have any input
>>>> on a quality way to perform guest attestation? If so, I'd be interested.
>>>
>>> I think what's missing is some clearer illustrations of how this
>>> feature is expected to be consumed in some real world application
>>> and the use cases we're trying to solve.
>>>
>>> I'd like to understand how it should fit in with common libvirt
>>> applications across the different virtualization management
>>> scenarios - eg virsh (command line), virt-manger (local desktop
>>> GUI), cockpit (single host web mgmt), OpenStack (cloud mgmt), etc.
>>> And of course any non-traditional virt use cases that might be
>>> relevant such as Kata.
>>
>> That's still not that clear; I know Alice and Sergio have some ideas
>> (cc'd).
>> There's also some standardisation efforts (e.g. https://www.potaroo.net/ietf/html/ids-wg-rats.html
>> and https://www.ietf.org/archive/id/draft-ietf-rats-architecture-00.html
>> ) - that I can't claim to fully understand.
>> However, there are some themes that are emerging:
>>
>> a) One use is to only allow a VM to access some private data once we
>> prove it's the VM we expect running in a secure/confidential system
>> b) (a) normally involves requesting some proof from the VM and then
>> providing it some confidential data/a key if it's OK
>> c) RATs splits the problem up:
>> https://www.ietf.org/archive/id/draft-ietf-rats-architecture-00.html#name-architectural-overview
>> I don't fully understand the split yet, but in principal there are
>> at least a few different things:
>>
>> d) The comms layer
>> e) Something that validates the attestation message (i.e. the
>> signatures are valid, the hashes all add up etc)
>> f) Something that knows what hashes to expect (i.e. oh that's a RHEL
>> 8.4 kernel, or that's a valid kernel command line)
>> g) Something that holds some secrets that can be handed out if e & f
>> are happy.
>>
>> There have also been proposals (e.g. Intel HTTPA) for an attestable
>> connection after a VM is running; that's probably quite different from
>> (g) but still involves (e) & (f).
>>
>> In the simpler setups d,e,f,g probably live in one place; but it's not
>> clear where they live - for example one scenario says that your cloud
>> management layer holds some of them, another says you don't trust your
>> cloud management layer and you keep them separate.
>>
>> So I think all we're actually interested in at the moment, is (d) and
>> (e) and the way for (g) to get the secret back to the guest.
>>
>> Unfortunately the comms and the contents of them varies heavily with
>> technology; in some you're talking to the qemu/hypervisor (SEV/SEV-ES)
>> while in some you're talking to the guest after boot (SEV-SNP/TDX maybe
>> SEV-ES in some cases).
SEV-ES has pre-launch measurement and secret injection, just like SEV
(except that the measurement includes the initial states of all vcpus,
that is, their VMSAs. BTW that means that in order to calculate the
measurement the Attestation Server must know exactly how many vcpus are
in the VM).
>>
>> So my expectation at the moment is libvirt needs to provide a transport
>> layer for the comms, to enable an external validator to retrieve the
>> measurements from the guest/hypervisor and provide data back if
>> necessary. Once this shakes out a bit, we might want libvirt to be
>> able to invoke the validator; however I expect (f) and (g) to be much
>> more complex things that don't feel like they belong in libvirt.
>
> We experimented with the attestation flow quite a bit while working on
> SEV-ES support for libkrun-tee. One important aspect we noticed quite
> early, is that there's more data that's needed to be exchange of top
> of the attestation itself.
>
> For instance, even before you start the VM, the management layer in
> charge of coordinating the confidential VM launch needs to obtain the
> Virtualization TEE capabilities of the Host (SEV-ES vs. SEV-SNP
> vs. TDX) and the platform version, to know which features are
> available and whether that host is a candidate for running the VM at
> all.
>
> With that information, the mgmt layer can build a guest policy (this
> is SEV's terminology, but I guess we'll have something similar in
> TDX) and feed it to component launching the VMM (libvirt, in this
> case).
>
> For SEV-SNP, this is pretty much the end of the story, because the
> attestation exchange is driven by an agent inside the guest. Well,
> there's also the need to have in the VM a well-known vNIC bridged to a
> network that's routed to the Attestation Server, that everyone seems
> to consider a given, but to me, from a CSP perspective, looks like
> quite a headache. In fact, I'd go as far as to suggest this
> communication should happen through an alternative channel, such as
> vsock, having a proxy on the Host, but I guess that depends on the CSP
> infrastructure.
If we have an alternative channel (vsock?) and a proxy on the host,
maybe we can share parts of the solution between SEV and SNP.
>
> For SEV/SEV-ES, as the attestation happens at the VMM level, there's
> still the need to have some interactions with it. As Tyler pointed
> out, we basically need to retrieve the measurement and, if valid,
> inject the secret. If the measurement isn't valid, the VM must be shut
> down immediately.
>
> In libkrun-tee, this operation is driven by the VMM in libkrun, which
> contacts the Attestation Server with the measurement and receives the
> secret in exchange. I guess for QEMU/libvirt we expect this to be
> driven by the upper management layer through a delegated component in
> the Host, such as NOVA. In this case, NOVA would need to:
>
> - Based on the upper management layer info and the Host properties,
> generate a guest policy and use it while generating the compute
> instance XML.
>
> - Ask libvirt to launch the VM.
Launch the VM with -S (suspended; so it doesn't actually begin running
guest instructions).
>
> - Wait for the VM to be in SEV_STATE_LAUNCH_SECRET state *.
>
> - Retrieve the measurement *.
Note that libvirt holds the QMP socket to QEMU. So whoever fetches the
measurement needs either (a) to ask libvirt to it; or (b) to connect to
another QMP listening socket for getting the measurement and injecting
the secret.
In Kata, Jim Cadden (cc'd) worked on adding this second QMP socket (if
I'm not mistaken) to the kata-runtime (which is the process that starts
QEMU and later controls it with QMP).
>
> - Contact the Attestation Server and provide it with some kind of
> information to uniquely identify the VM (needed to determine what's
> the expected measurement) and the measurement itself.
>
> * If the measurement if valid, inject the secret *.
>
> + The secret is pre-encrypted with a key that only the PSP has,
> so there's no need to do any special handling of it.
>
> - Ask libvirt to either destroy the VM (if the measurement wasn't
> valid or there was some kind of communication error with the
> Attestation Server) or continue the execution of the VM (this will
> be the first time kvm_vcpu_run() is entered).
>
> The operations marked with (*) are the ones that I'm not sure if
> NOVA should communicate with libvirt or talk directly to QEMU.
>
> Sergio.
>
On top of what's written above, note that with direct boot (with
-kernel/-initrd/-append) the hashes of these 3 elements may be inserted
into the guest measurement (with kernel-hashes=on option on object
sev-guest; upcoming in QEMU 6.2). This means that the Attestation
Server must know the OVMF hash as well as the hashes of kernel, initrd,
and cmdline in order to construct the expected measurement.
-Dov
^ permalink raw reply [flat|nested] 26+ messages in thread* Re: SEV guest attestation
2021-11-25 12:44 ` Dov Murik
@ 2021-11-25 13:42 ` Daniel P. Berrangé
2021-11-25 13:59 ` Dov Murik
2021-11-25 15:11 ` Sergio Lopez
1 sibling, 1 reply; 26+ messages in thread
From: Daniel P. Berrangé @ 2021-11-25 13:42 UTC (permalink / raw)
To: Dov Murik
Cc: Sergio Lopez, afrosi, James Bottomley, Dr. David Alan Gilbert,
qemu-devel, Hubertus Franke, Tyler Fanelli,
Tobin Feldman-Fitzthum, Jim Cadden, dinechin, John Ferlan
On Thu, Nov 25, 2021 at 02:44:51PM +0200, Dov Murik wrote:
> [+cc jejb, tobin, jim, hubertus]
>
>
> On 25/11/2021 9:14, Sergio Lopez wrote:
> > On Wed, Nov 24, 2021 at 06:29:07PM +0000, Dr. David Alan Gilbert wrote:
> >> * Daniel P. Berrangé (berrange@redhat.com) wrote:
> >>> On Wed, Nov 24, 2021 at 11:34:16AM -0500, Tyler Fanelli wrote:
> >>>> Hi,
> >>>>
> >>>> We recently discussed a way for remote SEV guest attestation through QEMU.
> >>>> My initial approach was to get data needed for attestation through different
> >>>> QMP commands (all of which are already available, so no changes required
> >>>> there), deriving hashes and certificate data; and collecting all of this
> >>>> into a new QMP struct (SevLaunchStart, which would include the VM's policy,
> >>>> secret, and GPA) which would need to be upstreamed into QEMU. Once this is
> >>>> provided, QEMU would then need to have support for attestation before a VM
> >>>> is started. Upon speaking to Dave about this proposal, he mentioned that
> >>>> this may not be the best approach, as some situations would render the
> >>>> attestation unavailable, such as the instance where a VM is running in a
> >>>> cloud, and a guest owner would like to perform attestation via QMP (a likely
> >>>> scenario), yet a cloud provider cannot simply let anyone pass arbitrary QMP
> >>>> commands, as this could be an issue.
> >>>
> >>> As a general point, QMP is a low level QEMU implementation detail,
> >>> which is generally expected to be consumed exclusively on the host
> >>> by a privileged mgmt layer, which will in turn expose its own higher
> >>> level APIs to users or other apps. I would not expect to see QMP
> >>> exposed to anything outside of the privileged host layer.
> >>>
> >>> We also use the QAPI protocol for QEMU guest agent commmunication,
> >>> however, that is a distinct service from QMP on the host. It shares
> >>> most infra with QMP but has a completely diffent command set. On the
> >>> host it is not consumed inside QEMU, but instead consumed by a
> >>> mgmt app like libvirt.
> >>>
> >>>> So I ask, does anyone involved in QEMU's SEV implementation have any input
> >>>> on a quality way to perform guest attestation? If so, I'd be interested.
> >>>
> >>> I think what's missing is some clearer illustrations of how this
> >>> feature is expected to be consumed in some real world application
> >>> and the use cases we're trying to solve.
> >>>
> >>> I'd like to understand how it should fit in with common libvirt
> >>> applications across the different virtualization management
> >>> scenarios - eg virsh (command line), virt-manger (local desktop
> >>> GUI), cockpit (single host web mgmt), OpenStack (cloud mgmt), etc.
> >>> And of course any non-traditional virt use cases that might be
> >>> relevant such as Kata.
> >>
> >> That's still not that clear; I know Alice and Sergio have some ideas
> >> (cc'd).
> >> There's also some standardisation efforts (e.g. https://www.potaroo.net/ietf/html/ids-wg-rats.html
> >> and https://www.ietf.org/archive/id/draft-ietf-rats-architecture-00.html
> >> ) - that I can't claim to fully understand.
> >> However, there are some themes that are emerging:
> >>
> >> a) One use is to only allow a VM to access some private data once we
> >> prove it's the VM we expect running in a secure/confidential system
> >> b) (a) normally involves requesting some proof from the VM and then
> >> providing it some confidential data/a key if it's OK
> >> c) RATs splits the problem up:
> >> https://www.ietf.org/archive/id/draft-ietf-rats-architecture-00.html#name-architectural-overview
> >> I don't fully understand the split yet, but in principal there are
> >> at least a few different things:
> >>
> >> d) The comms layer
> >> e) Something that validates the attestation message (i.e. the
> >> signatures are valid, the hashes all add up etc)
> >> f) Something that knows what hashes to expect (i.e. oh that's a RHEL
> >> 8.4 kernel, or that's a valid kernel command line)
> >> g) Something that holds some secrets that can be handed out if e & f
> >> are happy.
> >>
> >> There have also been proposals (e.g. Intel HTTPA) for an attestable
> >> connection after a VM is running; that's probably quite different from
> >> (g) but still involves (e) & (f).
> >>
> >> In the simpler setups d,e,f,g probably live in one place; but it's not
> >> clear where they live - for example one scenario says that your cloud
> >> management layer holds some of them, another says you don't trust your
> >> cloud management layer and you keep them separate.
> >>
> >> So I think all we're actually interested in at the moment, is (d) and
> >> (e) and the way for (g) to get the secret back to the guest.
> >>
> >> Unfortunately the comms and the contents of them varies heavily with
> >> technology; in some you're talking to the qemu/hypervisor (SEV/SEV-ES)
> >> while in some you're talking to the guest after boot (SEV-SNP/TDX maybe
> >> SEV-ES in some cases).
>
> SEV-ES has pre-launch measurement and secret injection, just like SEV
> (except that the measurement includes the initial states of all vcpus,
> that is, their VMSAs. BTW that means that in order to calculate the
> measurement the Attestation Server must know exactly how many vcpus are
> in the VM).
Does that work with CPU hotplug ? ie cold boot with -smp 4,maxcpus=8
and some time later try to enable the extra 4 cpus at runtime ?
> >> So my expectation at the moment is libvirt needs to provide a transport
> >> layer for the comms, to enable an external validator to retrieve the
> >> measurements from the guest/hypervisor and provide data back if
> >> necessary. Once this shakes out a bit, we might want libvirt to be
> >> able to invoke the validator; however I expect (f) and (g) to be much
> >> more complex things that don't feel like they belong in libvirt.
> >
> > We experimented with the attestation flow quite a bit while working on
> > SEV-ES support for libkrun-tee. One important aspect we noticed quite
> > early, is that there's more data that's needed to be exchange of top
> > of the attestation itself.
> >
> > For instance, even before you start the VM, the management layer in
> > charge of coordinating the confidential VM launch needs to obtain the
> > Virtualization TEE capabilities of the Host (SEV-ES vs. SEV-SNP
> > vs. TDX) and the platform version, to know which features are
> > available and whether that host is a candidate for running the VM at
> > all.
> >
> > With that information, the mgmt layer can build a guest policy (this
> > is SEV's terminology, but I guess we'll have something similar in
> > TDX) and feed it to component launching the VMM (libvirt, in this
> > case).
> >
> > For SEV-SNP, this is pretty much the end of the story, because the
> > attestation exchange is driven by an agent inside the guest. Well,
> > there's also the need to have in the VM a well-known vNIC bridged to a
> > network that's routed to the Attestation Server, that everyone seems
> > to consider a given, but to me, from a CSP perspective, looks like
> > quite a headache. In fact, I'd go as far as to suggest this
> > communication should happen through an alternative channel, such as
> > vsock, having a proxy on the Host, but I guess that depends on the CSP
> > infrastructure.
>
> If we have an alternative channel (vsock?) and a proxy on the host,
> maybe we can share parts of the solution between SEV and SNP.
>
>
> > For SEV/SEV-ES, as the attestation happens at the VMM level, there's
> > still the need to have some interactions with it. As Tyler pointed
> > out, we basically need to retrieve the measurement and, if valid,
> > inject the secret. If the measurement isn't valid, the VM must be shut
> > down immediately.
> >
> > In libkrun-tee, this operation is driven by the VMM in libkrun, which
> > contacts the Attestation Server with the measurement and receives the
> > secret in exchange. I guess for QEMU/libvirt we expect this to be
> > driven by the upper management layer through a delegated component in
> > the Host, such as NOVA. In this case, NOVA would need to:
> >
> > - Based on the upper management layer info and the Host properties,
> > generate a guest policy and use it while generating the compute
> > instance XML.
> >
> > - Ask libvirt to launch the VM.
>
> Launch the VM with -S (suspended; so it doesn't actually begin running
> guest instructions).
>
>
> >
> > - Wait for the VM to be in SEV_STATE_LAUNCH_SECRET state *.
> >
> > - Retrieve the measurement *.
>
> Note that libvirt holds the QMP socket to QEMU. So whoever fetches the
> measurement needs either (a) to ask libvirt to it; or (b) to connect to
> another QMP listening socket for getting the measurement and injecting
> the secret.
Libvirt would not be particularly happy with allowing (b) because it
enables the 3rd parties to change the VM state behind libvirt's back
in ways that can ultimately confuse its understanding of the state
of the VM. If there's some task that needs interaction with a QEMU
managed by libvirt, we need to expose suitable APIs in libvirt (if
they don't already exist).
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 :|
^ permalink raw reply [flat|nested] 26+ messages in thread
* Re: SEV guest attestation
2021-11-25 13:42 ` Daniel P. Berrangé
@ 2021-11-25 13:59 ` Dov Murik
2021-11-29 14:29 ` Brijesh Singh
0 siblings, 1 reply; 26+ messages in thread
From: Dov Murik @ 2021-11-25 13:59 UTC (permalink / raw)
To: Daniel P. Berrangé, Tom Lendacky, Brijesh Singh
Cc: Dov Murik, Sergio Lopez, afrosi, James Bottomley,
Dr. David Alan Gilbert, qemu-devel, Hubertus Franke,
Tyler Fanelli, Tobin Feldman-Fitzthum, Jim Cadden, dinechin,
John Ferlan
[+cc Tom, Brijesh]
On 25/11/2021 15:42, Daniel P. Berrangé wrote:
> On Thu, Nov 25, 2021 at 02:44:51PM +0200, Dov Murik wrote:
>> [+cc jejb, tobin, jim, hubertus]
>>
>>
>> On 25/11/2021 9:14, Sergio Lopez wrote:
>>> On Wed, Nov 24, 2021 at 06:29:07PM +0000, Dr. David Alan Gilbert wrote:
>>>> * Daniel P. Berrangé (berrange@redhat.com) wrote:
>>>>> On Wed, Nov 24, 2021 at 11:34:16AM -0500, Tyler Fanelli wrote:
>>>>>> Hi,
>>>>>>
>>>>>> We recently discussed a way for remote SEV guest attestation through QEMU.
>>>>>> My initial approach was to get data needed for attestation through different
>>>>>> QMP commands (all of which are already available, so no changes required
>>>>>> there), deriving hashes and certificate data; and collecting all of this
>>>>>> into a new QMP struct (SevLaunchStart, which would include the VM's policy,
>>>>>> secret, and GPA) which would need to be upstreamed into QEMU. Once this is
>>>>>> provided, QEMU would then need to have support for attestation before a VM
>>>>>> is started. Upon speaking to Dave about this proposal, he mentioned that
>>>>>> this may not be the best approach, as some situations would render the
>>>>>> attestation unavailable, such as the instance where a VM is running in a
>>>>>> cloud, and a guest owner would like to perform attestation via QMP (a likely
>>>>>> scenario), yet a cloud provider cannot simply let anyone pass arbitrary QMP
>>>>>> commands, as this could be an issue.
>>>>>
>>>>> As a general point, QMP is a low level QEMU implementation detail,
>>>>> which is generally expected to be consumed exclusively on the host
>>>>> by a privileged mgmt layer, which will in turn expose its own higher
>>>>> level APIs to users or other apps. I would not expect to see QMP
>>>>> exposed to anything outside of the privileged host layer.
>>>>>
>>>>> We also use the QAPI protocol for QEMU guest agent commmunication,
>>>>> however, that is a distinct service from QMP on the host. It shares
>>>>> most infra with QMP but has a completely diffent command set. On the
>>>>> host it is not consumed inside QEMU, but instead consumed by a
>>>>> mgmt app like libvirt.
>>>>>
>>>>>> So I ask, does anyone involved in QEMU's SEV implementation have any input
>>>>>> on a quality way to perform guest attestation? If so, I'd be interested.
>>>>>
>>>>> I think what's missing is some clearer illustrations of how this
>>>>> feature is expected to be consumed in some real world application
>>>>> and the use cases we're trying to solve.
>>>>>
>>>>> I'd like to understand how it should fit in with common libvirt
>>>>> applications across the different virtualization management
>>>>> scenarios - eg virsh (command line), virt-manger (local desktop
>>>>> GUI), cockpit (single host web mgmt), OpenStack (cloud mgmt), etc.
>>>>> And of course any non-traditional virt use cases that might be
>>>>> relevant such as Kata.
>>>>
>>>> That's still not that clear; I know Alice and Sergio have some ideas
>>>> (cc'd).
>>>> There's also some standardisation efforts (e.g. https://www.potaroo.net/ietf/html/ids-wg-rats.html
>>>> and https://www.ietf.org/archive/id/draft-ietf-rats-architecture-00.html
>>>> ) - that I can't claim to fully understand.
>>>> However, there are some themes that are emerging:
>>>>
>>>> a) One use is to only allow a VM to access some private data once we
>>>> prove it's the VM we expect running in a secure/confidential system
>>>> b) (a) normally involves requesting some proof from the VM and then
>>>> providing it some confidential data/a key if it's OK
>>>> c) RATs splits the problem up:
>>>> https://www.ietf.org/archive/id/draft-ietf-rats-architecture-00.html#name-architectural-overview
>>>> I don't fully understand the split yet, but in principal there are
>>>> at least a few different things:
>>>>
>>>> d) The comms layer
>>>> e) Something that validates the attestation message (i.e. the
>>>> signatures are valid, the hashes all add up etc)
>>>> f) Something that knows what hashes to expect (i.e. oh that's a RHEL
>>>> 8.4 kernel, or that's a valid kernel command line)
>>>> g) Something that holds some secrets that can be handed out if e & f
>>>> are happy.
>>>>
>>>> There have also been proposals (e.g. Intel HTTPA) for an attestable
>>>> connection after a VM is running; that's probably quite different from
>>>> (g) but still involves (e) & (f).
>>>>
>>>> In the simpler setups d,e,f,g probably live in one place; but it's not
>>>> clear where they live - for example one scenario says that your cloud
>>>> management layer holds some of them, another says you don't trust your
>>>> cloud management layer and you keep them separate.
>>>>
>>>> So I think all we're actually interested in at the moment, is (d) and
>>>> (e) and the way for (g) to get the secret back to the guest.
>>>>
>>>> Unfortunately the comms and the contents of them varies heavily with
>>>> technology; in some you're talking to the qemu/hypervisor (SEV/SEV-ES)
>>>> while in some you're talking to the guest after boot (SEV-SNP/TDX maybe
>>>> SEV-ES in some cases).
>>
>> SEV-ES has pre-launch measurement and secret injection, just like SEV
>> (except that the measurement includes the initial states of all vcpus,
>> that is, their VMSAs. BTW that means that in order to calculate the
>> measurement the Attestation Server must know exactly how many vcpus are
>> in the VM).
>
> Does that work with CPU hotplug ? ie cold boot with -smp 4,maxcpus=8
> and some time later try to enable the extra 4 cpus at runtime ?
>
AFAIK all generations of SEV don't support CPU hotplug. Tom, Brijesh -
is that indeed the case?
I don't know about TDX.
-Dov
>
>>>> So my expectation at the moment is libvirt needs to provide a transport
>>>> layer for the comms, to enable an external validator to retrieve the
>>>> measurements from the guest/hypervisor and provide data back if
>>>> necessary. Once this shakes out a bit, we might want libvirt to be
>>>> able to invoke the validator; however I expect (f) and (g) to be much
>>>> more complex things that don't feel like they belong in libvirt.
>>>
>>> We experimented with the attestation flow quite a bit while working on
>>> SEV-ES support for libkrun-tee. One important aspect we noticed quite
>>> early, is that there's more data that's needed to be exchange of top
>>> of the attestation itself.
>>>
>>> For instance, even before you start the VM, the management layer in
>>> charge of coordinating the confidential VM launch needs to obtain the
>>> Virtualization TEE capabilities of the Host (SEV-ES vs. SEV-SNP
>>> vs. TDX) and the platform version, to know which features are
>>> available and whether that host is a candidate for running the VM at
>>> all.
>>>
>>> With that information, the mgmt layer can build a guest policy (this
>>> is SEV's terminology, but I guess we'll have something similar in
>>> TDX) and feed it to component launching the VMM (libvirt, in this
>>> case).
>>>
>>> For SEV-SNP, this is pretty much the end of the story, because the
>>> attestation exchange is driven by an agent inside the guest. Well,
>>> there's also the need to have in the VM a well-known vNIC bridged to a
>>> network that's routed to the Attestation Server, that everyone seems
>>> to consider a given, but to me, from a CSP perspective, looks like
>>> quite a headache. In fact, I'd go as far as to suggest this
>>> communication should happen through an alternative channel, such as
>>> vsock, having a proxy on the Host, but I guess that depends on the CSP
>>> infrastructure.
>>
>> If we have an alternative channel (vsock?) and a proxy on the host,
>> maybe we can share parts of the solution between SEV and SNP.
>>
>>
>>> For SEV/SEV-ES, as the attestation happens at the VMM level, there's
>>> still the need to have some interactions with it. As Tyler pointed
>>> out, we basically need to retrieve the measurement and, if valid,
>>> inject the secret. If the measurement isn't valid, the VM must be shut
>>> down immediately.
>>>
>>> In libkrun-tee, this operation is driven by the VMM in libkrun, which
>>> contacts the Attestation Server with the measurement and receives the
>>> secret in exchange. I guess for QEMU/libvirt we expect this to be
>>> driven by the upper management layer through a delegated component in
>>> the Host, such as NOVA. In this case, NOVA would need to:
>>>
>>> - Based on the upper management layer info and the Host properties,
>>> generate a guest policy and use it while generating the compute
>>> instance XML.
>>>
>>> - Ask libvirt to launch the VM.
>>
>> Launch the VM with -S (suspended; so it doesn't actually begin running
>> guest instructions).
>>
>>
>>>
>>> - Wait for the VM to be in SEV_STATE_LAUNCH_SECRET state *.
>>>
>>> - Retrieve the measurement *.
>>
>> Note that libvirt holds the QMP socket to QEMU. So whoever fetches the
>> measurement needs either (a) to ask libvirt to it; or (b) to connect to
>> another QMP listening socket for getting the measurement and injecting
>> the secret.
>
> Libvirt would not be particularly happy with allowing (b) because it
> enables the 3rd parties to change the VM state behind libvirt's back
> in ways that can ultimately confuse its understanding of the state
> of the VM. If there's some task that needs interaction with a QEMU
> managed by libvirt, we need to expose suitable APIs in libvirt (if
> they don't already exist).
>
>
> Regards,
> Daniel
>
^ permalink raw reply [flat|nested] 26+ messages in thread
* Re: SEV guest attestation
2021-11-25 13:59 ` Dov Murik
@ 2021-11-29 14:29 ` Brijesh Singh
2021-11-29 14:49 ` Brijesh Singh
0 siblings, 1 reply; 26+ messages in thread
From: Brijesh Singh @ 2021-11-29 14:29 UTC (permalink / raw)
To: Dov Murik, Daniel P. Berrangé, Tom Lendacky
Cc: brijesh.singh, Sergio Lopez, Dr. David Alan Gilbert,
Tyler Fanelli, afrosi, qemu-devel, dinechin, John Ferlan,
James Bottomley, Tobin Feldman-Fitzthum, Jim Cadden,
Hubertus Franke
On 11/25/21 7:59 AM, Dov Murik wrote:
> [+cc Tom, Brijesh]
>
> On 25/11/2021 15:42, Daniel P. Berrangé wrote:
>> On Thu, Nov 25, 2021 at 02:44:51PM +0200, Dov Murik wrote:
>>> [+cc jejb, tobin, jim, hubertus]
>>>
>>>
>>> On 25/11/2021 9:14, Sergio Lopez wrote:
>>>> On Wed, Nov 24, 2021 at 06:29:07PM +0000, Dr. David Alan Gilbert wrote:
>>>>> * Daniel P. Berrangé (berrange@redhat.com) wrote:
>>>>>> On Wed, Nov 24, 2021 at 11:34:16AM -0500, Tyler Fanelli wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> We recently discussed a way for remote SEV guest attestation through QEMU.
>>>>>>> My initial approach was to get data needed for attestation through different
>>>>>>> QMP commands (all of which are already available, so no changes required
>>>>>>> there), deriving hashes and certificate data; and collecting all of this
>>>>>>> into a new QMP struct (SevLaunchStart, which would include the VM's policy,
>>>>>>> secret, and GPA) which would need to be upstreamed into QEMU. Once this is
>>>>>>> provided, QEMU would then need to have support for attestation before a VM
>>>>>>> is started. Upon speaking to Dave about this proposal, he mentioned that
>>>>>>> this may not be the best approach, as some situations would render the
>>>>>>> attestation unavailable, such as the instance where a VM is running in a
>>>>>>> cloud, and a guest owner would like to perform attestation via QMP (a likely
>>>>>>> scenario), yet a cloud provider cannot simply let anyone pass arbitrary QMP
>>>>>>> commands, as this could be an issue.
>>>>>>
>>>>>> As a general point, QMP is a low level QEMU implementation detail,
>>>>>> which is generally expected to be consumed exclusively on the host
>>>>>> by a privileged mgmt layer, which will in turn expose its own higher
>>>>>> level APIs to users or other apps. I would not expect to see QMP
>>>>>> exposed to anything outside of the privileged host layer.
>>>>>>
>>>>>> We also use the QAPI protocol for QEMU guest agent commmunication,
>>>>>> however, that is a distinct service from QMP on the host. It shares
>>>>>> most infra with QMP but has a completely diffent command set. On the
>>>>>> host it is not consumed inside QEMU, but instead consumed by a
>>>>>> mgmt app like libvirt.
>>>>>>
>>>>>>> So I ask, does anyone involved in QEMU's SEV implementation have any input
>>>>>>> on a quality way to perform guest attestation? If so, I'd be interested.
>>>>>>
>>>>>> I think what's missing is some clearer illustrations of how this
>>>>>> feature is expected to be consumed in some real world application
>>>>>> and the use cases we're trying to solve.
>>>>>>
>>>>>> I'd like to understand how it should fit in with common libvirt
>>>>>> applications across the different virtualization management
>>>>>> scenarios - eg virsh (command line), virt-manger (local desktop
>>>>>> GUI), cockpit (single host web mgmt), OpenStack (cloud mgmt), etc.
>>>>>> And of course any non-traditional virt use cases that might be
>>>>>> relevant such as Kata.
>>>>>
>>>>> That's still not that clear; I know Alice and Sergio have some ideas
>>>>> (cc'd).
>>>>> There's also some standardisation efforts (e.g. https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.potaroo.net%2Fietf%2Fhtml%2Fids-wg-rats.html&data=04%7C01%7Cbrijesh.singh%40amd.com%7C3c94b09f0cd5450460a808d9b01be1f8%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637734456065941078%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=E%2FeaI6JNF2ckosTeAbFRaCZUJOZ3zG0GNfKP8082INQ%3D&reserved=0
>>>>> and https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ietf.org%2Farchive%2Fid%2Fdraft-ietf-rats-architecture-00.html&data=04%7C01%7Cbrijesh.singh%40amd.com%7C3c94b09f0cd5450460a808d9b01be1f8%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637734456065951077%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=WEkMIZZp3O5Gyay5jZT8KSUH9fyarNfXy5O0Z%2FpHdnQ%3D&reserved=0
>>>>> ) - that I can't claim to fully understand.
>>>>> However, there are some themes that are emerging:
>>>>>
>>>>> a) One use is to only allow a VM to access some private data once we
>>>>> prove it's the VM we expect running in a secure/confidential system
>>>>> b) (a) normally involves requesting some proof from the VM and then
>>>>> providing it some confidential data/a key if it's OK
>>>>> c) RATs splits the problem up:
>>>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ietf.org%2Farchive%2Fid%2Fdraft-ietf-rats-architecture-00.html%23name-architectural-overview&data=04%7C01%7Cbrijesh.singh%40amd.com%7C3c94b09f0cd5450460a808d9b01be1f8%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637734456065951077%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=%2FwNFMGAfojFZyGIj79D5%2BW%2BRPPuwumJiqIrf5UVrkPU%3D&reserved=0
>>>>> I don't fully understand the split yet, but in principal there are
>>>>> at least a few different things:
>>>>>
>>>>> d) The comms layer
>>>>> e) Something that validates the attestation message (i.e. the
>>>>> signatures are valid, the hashes all add up etc)
>>>>> f) Something that knows what hashes to expect (i.e. oh that's a RHEL
>>>>> 8.4 kernel, or that's a valid kernel command line)
>>>>> g) Something that holds some secrets that can be handed out if e & f
>>>>> are happy.
>>>>>
>>>>> There have also been proposals (e.g. Intel HTTPA) for an attestable
>>>>> connection after a VM is running; that's probably quite different from
>>>>> (g) but still involves (e) & (f).
>>>>>
>>>>> In the simpler setups d,e,f,g probably live in one place; but it's not
>>>>> clear where they live - for example one scenario says that your cloud
>>>>> management layer holds some of them, another says you don't trust your
>>>>> cloud management layer and you keep them separate.
>>>>>
>>>>> So I think all we're actually interested in at the moment, is (d) and
>>>>> (e) and the way for (g) to get the secret back to the guest.
>>>>>
>>>>> Unfortunately the comms and the contents of them varies heavily with
>>>>> technology; in some you're talking to the qemu/hypervisor (SEV/SEV-ES)
>>>>> while in some you're talking to the guest after boot (SEV-SNP/TDX maybe
>>>>> SEV-ES in some cases).
>>>
>>> SEV-ES has pre-launch measurement and secret injection, just like SEV
>>> (except that the measurement includes the initial states of all vcpus,
>>> that is, their VMSAs. BTW that means that in order to calculate the
>>> measurement the Attestation Server must know exactly how many vcpus are
>>> in the VM).
>>
>> Does that work with CPU hotplug ? ie cold boot with -smp 4,maxcpus=8
>> and some time later try to enable the extra 4 cpus at runtime ?
>>
>
> AFAIK all generations of SEV don't support CPU hotplug. Tom, Brijesh -
> is that indeed the case?
>
I think we may able to do a CPU hotplug on SEV but hotplug will not work
for the SEV-ES and SEV-SNP. This is mainly because the register state
need to be measured before the boot.
> I don't know about TDX.
>
> -Dov
>
>
>>
>>>>> So my expectation at the moment is libvirt needs to provide a transport
>>>>> layer for the comms, to enable an external validator to retrieve the
>>>>> measurements from the guest/hypervisor and provide data back if
>>>>> necessary. Once this shakes out a bit, we might want libvirt to be
>>>>> able to invoke the validator; however I expect (f) and (g) to be much
>>>>> more complex things that don't feel like they belong in libvirt.
>>>>
>>>> We experimented with the attestation flow quite a bit while working on
>>>> SEV-ES support for libkrun-tee. One important aspect we noticed quite
>>>> early, is that there's more data that's needed to be exchange of top
>>>> of the attestation itself.
>>>>
>>>> For instance, even before you start the VM, the management layer in
>>>> charge of coordinating the confidential VM launch needs to obtain the
>>>> Virtualization TEE capabilities of the Host (SEV-ES vs. SEV-SNP
>>>> vs. TDX) and the platform version, to know which features are
>>>> available and whether that host is a candidate for running the VM at
>>>> all.
>>>>
>>>> With that information, the mgmt layer can build a guest policy (this
>>>> is SEV's terminology, but I guess we'll have something similar in
>>>> TDX) and feed it to component launching the VMM (libvirt, in this
>>>> case).
>>>>
>>>> For SEV-SNP, this is pretty much the end of the story, because the
>>>> attestation exchange is driven by an agent inside the guest. Well,
>>>> there's also the need to have in the VM a well-known vNIC bridged to a
>>>> network that's routed to the Attestation Server, that everyone seems
>>>> to consider a given, but to me, from a CSP perspective, looks like
>>>> quite a headache. In fact, I'd go as far as to suggest this
>>>> communication should happen through an alternative channel, such as
>>>> vsock, having a proxy on the Host, but I guess that depends on the CSP
>>>> infrastructure.
>>>
>>> If we have an alternative channel (vsock?) and a proxy on the host,
>>> maybe we can share parts of the solution between SEV and SNP.
>>>
>>>
>>>> For SEV/SEV-ES, as the attestation happens at the VMM level, there's
>>>> still the need to have some interactions with it. As Tyler pointed
>>>> out, we basically need to retrieve the measurement and, if valid,
>>>> inject the secret. If the measurement isn't valid, the VM must be shut
>>>> down immediately.
>>>>
>>>> In libkrun-tee, this operation is driven by the VMM in libkrun, which
>>>> contacts the Attestation Server with the measurement and receives the
>>>> secret in exchange. I guess for QEMU/libvirt we expect this to be
>>>> driven by the upper management layer through a delegated component in
>>>> the Host, such as NOVA. In this case, NOVA would need to:
>>>>
>>>> - Based on the upper management layer info and the Host properties,
>>>> generate a guest policy and use it while generating the compute
>>>> instance XML.
>>>>
>>>> - Ask libvirt to launch the VM.
>>>
>>> Launch the VM with -S (suspended; so it doesn't actually begin running
>>> guest instructions).
>>>
>>>
>>>>
>>>> - Wait for the VM to be in SEV_STATE_LAUNCH_SECRET state *.
>>>>
>>>> - Retrieve the measurement *.
>>>
>>> Note that libvirt holds the QMP socket to QEMU. So whoever fetches the
>>> measurement needs either (a) to ask libvirt to it; or (b) to connect to
>>> another QMP listening socket for getting the measurement and injecting
>>> the secret.
>>
>> Libvirt would not be particularly happy with allowing (b) because it
>> enables the 3rd parties to change the VM state behind libvirt's back
>> in ways that can ultimately confuse its understanding of the state
>> of the VM. If there's some task that needs interaction with a QEMU
>> managed by libvirt, we need to expose suitable APIs in libvirt (if
>> they don't already exist).
>>
>>
>> Regards,
>> Daniel
>>
^ permalink raw reply [flat|nested] 26+ messages in thread
* Re: SEV guest attestation
2021-11-29 14:29 ` Brijesh Singh
@ 2021-11-29 14:49 ` Brijesh Singh
0 siblings, 0 replies; 26+ messages in thread
From: Brijesh Singh @ 2021-11-29 14:49 UTC (permalink / raw)
To: Dov Murik, Daniel P. Berrangé, Tom Lendacky
Cc: brijesh.singh, Sergio Lopez, Dr. David Alan Gilbert,
Tyler Fanelli, afrosi, qemu-devel, dinechin, John Ferlan,
James Bottomley, Tobin Feldman-Fitzthum, Jim Cadden,
Hubertus Franke
On 11/29/21 8:29 AM, Brijesh Singh wrote:
>
>
> On 11/25/21 7:59 AM, Dov Murik wrote:
>> [+cc Tom, Brijesh]
>>
>> On 25/11/2021 15:42, Daniel P. Berrangé wrote:
>>> On Thu, Nov 25, 2021 at 02:44:51PM +0200, Dov Murik wrote:
>>>> [+cc jejb, tobin, jim, hubertus]
>>>>
>>>>
>>>> On 25/11/2021 9:14, Sergio Lopez wrote:
>>>>> On Wed, Nov 24, 2021 at 06:29:07PM +0000, Dr. David Alan Gilbert
>>>>> wrote:
>>>>>> * Daniel P. Berrangé (berrange@redhat.com) wrote:
>>>>>>> On Wed, Nov 24, 2021 at 11:34:16AM -0500, Tyler Fanelli wrote:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> We recently discussed a way for remote SEV guest attestation
>>>>>>>> through QEMU.
>>>>>>>> My initial approach was to get data needed for attestation
>>>>>>>> through different
>>>>>>>> QMP commands (all of which are already available, so no changes
>>>>>>>> required
>>>>>>>> there), deriving hashes and certificate data; and collecting all
>>>>>>>> of this
>>>>>>>> into a new QMP struct (SevLaunchStart, which would include the
>>>>>>>> VM's policy,
>>>>>>>> secret, and GPA) which would need to be upstreamed into QEMU.
>>>>>>>> Once this is
>>>>>>>> provided, QEMU would then need to have support for attestation
>>>>>>>> before a VM
>>>>>>>> is started. Upon speaking to Dave about this proposal, he
>>>>>>>> mentioned that
>>>>>>>> this may not be the best approach, as some situations would
>>>>>>>> render the
>>>>>>>> attestation unavailable, such as the instance where a VM is
>>>>>>>> running in a
>>>>>>>> cloud, and a guest owner would like to perform attestation via
>>>>>>>> QMP (a likely
>>>>>>>> scenario), yet a cloud provider cannot simply let anyone pass
>>>>>>>> arbitrary QMP
>>>>>>>> commands, as this could be an issue.
>>>>>>>
>>>>>>> As a general point, QMP is a low level QEMU implementation detail,
>>>>>>> which is generally expected to be consumed exclusively on the host
>>>>>>> by a privileged mgmt layer, which will in turn expose its own higher
>>>>>>> level APIs to users or other apps. I would not expect to see QMP
>>>>>>> exposed to anything outside of the privileged host layer.
>>>>>>>
>>>>>>> We also use the QAPI protocol for QEMU guest agent commmunication,
>>>>>>> however, that is a distinct service from QMP on the host. It shares
>>>>>>> most infra with QMP but has a completely diffent command set. On the
>>>>>>> host it is not consumed inside QEMU, but instead consumed by a
>>>>>>> mgmt app like libvirt.
>>>>>>>
>>>>>>>> So I ask, does anyone involved in QEMU's SEV implementation have
>>>>>>>> any input
>>>>>>>> on a quality way to perform guest attestation? If so, I'd be
>>>>>>>> interested.
>>>>>>>
>>>>>>> I think what's missing is some clearer illustrations of how this
>>>>>>> feature is expected to be consumed in some real world application
>>>>>>> and the use cases we're trying to solve.
>>>>>>>
>>>>>>> I'd like to understand how it should fit in with common libvirt
>>>>>>> applications across the different virtualization management
>>>>>>> scenarios - eg virsh (command line), virt-manger (local desktop
>>>>>>> GUI), cockpit (single host web mgmt), OpenStack (cloud mgmt), etc.
>>>>>>> And of course any non-traditional virt use cases that might be
>>>>>>> relevant such as Kata.
>>>>>>
>>>>>> That's still not that clear; I know Alice and Sergio have some ideas
>>>>>> (cc'd).
>>>>>> There's also some standardisation efforts (e.g.
>>>>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.potaroo.net%2Fietf%2Fhtml%2Fids-wg-rats.html&data=04%7C01%7Cbrijesh.singh%40amd.com%7C3c94b09f0cd5450460a808d9b01be1f8%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637734456065941078%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=E%2FeaI6JNF2ckosTeAbFRaCZUJOZ3zG0GNfKP8082INQ%3D&reserved=0
>>>>>>
>>>>>> and
>>>>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ietf.org%2Farchive%2Fid%2Fdraft-ietf-rats-architecture-00.html&data=04%7C01%7Cbrijesh.singh%40amd.com%7C3c94b09f0cd5450460a808d9b01be1f8%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637734456065951077%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=WEkMIZZp3O5Gyay5jZT8KSUH9fyarNfXy5O0Z%2FpHdnQ%3D&reserved=0
>>>>>>
>>>>>> ) - that I can't claim to fully understand.
>>>>>> However, there are some themes that are emerging:
>>>>>>
>>>>>> a) One use is to only allow a VM to access some private data
>>>>>> once we
>>>>>> prove it's the VM we expect running in a secure/confidential system
>>>>>> b) (a) normally involves requesting some proof from the VM and
>>>>>> then
>>>>>> providing it some confidential data/a key if it's OK
>>>>>> c) RATs splits the problem up:
>>>>>>
>>>>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ietf.org%2Farchive%2Fid%2Fdraft-ietf-rats-architecture-00.html%23name-architectural-overview&data=04%7C01%7Cbrijesh.singh%40amd.com%7C3c94b09f0cd5450460a808d9b01be1f8%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637734456065951077%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=%2FwNFMGAfojFZyGIj79D5%2BW%2BRPPuwumJiqIrf5UVrkPU%3D&reserved=0
>>>>>>
>>>>>> I don't fully understand the split yet, but in principal
>>>>>> there are
>>>>>> at least a few different things:
>>>>>>
>>>>>> d) The comms layer
>>>>>> e) Something that validates the attestation message (i.e. the
>>>>>> signatures are valid, the hashes all add up etc)
>>>>>> f) Something that knows what hashes to expect (i.e. oh that's a
>>>>>> RHEL
>>>>>> 8.4 kernel, or that's a valid kernel command line)
>>>>>> g) Something that holds some secrets that can be handed out if
>>>>>> e & f
>>>>>> are happy.
>>>>>>
>>>>>> There have also been proposals (e.g. Intel HTTPA) for an
>>>>>> attestable
>>>>>> connection after a VM is running; that's probably quite different
>>>>>> from
>>>>>> (g) but still involves (e) & (f).
>>>>>>
>>>>>> In the simpler setups d,e,f,g probably live in one place; but it's
>>>>>> not
>>>>>> clear where they live - for example one scenario says that your cloud
>>>>>> management layer holds some of them, another says you don't trust
>>>>>> your
>>>>>> cloud management layer and you keep them separate.
>>>>>>
>>>>>> So I think all we're actually interested in at the moment, is (d) and
>>>>>> (e) and the way for (g) to get the secret back to the guest.
>>>>>>
>>>>>> Unfortunately the comms and the contents of them varies heavily with
>>>>>> technology; in some you're talking to the qemu/hypervisor
>>>>>> (SEV/SEV-ES)
>>>>>> while in some you're talking to the guest after boot (SEV-SNP/TDX
>>>>>> maybe
>>>>>> SEV-ES in some cases).
>>>>
>>>> SEV-ES has pre-launch measurement and secret injection, just like SEV
>>>> (except that the measurement includes the initial states of all vcpus,
>>>> that is, their VMSAs. BTW that means that in order to calculate the
>>>> measurement the Attestation Server must know exactly how many vcpus are
>>>> in the VM).
>>>
>>> Does that work with CPU hotplug ? ie cold boot with -smp 4,maxcpus=8
>>> and some time later try to enable the extra 4 cpus at runtime ?
>>>
>>
>> AFAIK all generations of SEV don't support CPU hotplug. Tom, Brijesh -
>> is that indeed the case?
>>
>
> I think we may able to do a CPU hotplug on SEV but hotplug will not work
> for the SEV-ES and SEV-SNP. This is mainly because the register state
> need to be measured before the boot.
Tom just pointed me out, theoretically we could do a hotplug of CPUs
under the SEV-SNP but I will need to check the security team just to be
sure that we are good from the attestation flow. I can update you guys
on it.
thanks
>
>> I don't know about TDX.
>>
>> -Dov
>>
>>
>>>
>>>>>> So my expectation at the moment is libvirt needs to provide a
>>>>>> transport
>>>>>> layer for the comms, to enable an external validator to retrieve the
>>>>>> measurements from the guest/hypervisor and provide data back if
>>>>>> necessary. Once this shakes out a bit, we might want libvirt to be
>>>>>> able to invoke the validator; however I expect (f) and (g) to be much
>>>>>> more complex things that don't feel like they belong in libvirt.
>>>>>
>>>>> We experimented with the attestation flow quite a bit while working on
>>>>> SEV-ES support for libkrun-tee. One important aspect we noticed quite
>>>>> early, is that there's more data that's needed to be exchange of top
>>>>> of the attestation itself.
>>>>>
>>>>> For instance, even before you start the VM, the management layer in
>>>>> charge of coordinating the confidential VM launch needs to obtain the
>>>>> Virtualization TEE capabilities of the Host (SEV-ES vs. SEV-SNP
>>>>> vs. TDX) and the platform version, to know which features are
>>>>> available and whether that host is a candidate for running the VM at
>>>>> all.
>>>>>
>>>>> With that information, the mgmt layer can build a guest policy (this
>>>>> is SEV's terminology, but I guess we'll have something similar in
>>>>> TDX) and feed it to component launching the VMM (libvirt, in this
>>>>> case).
>>>>>
>>>>> For SEV-SNP, this is pretty much the end of the story, because the
>>>>> attestation exchange is driven by an agent inside the guest. Well,
>>>>> there's also the need to have in the VM a well-known vNIC bridged to a
>>>>> network that's routed to the Attestation Server, that everyone seems
>>>>> to consider a given, but to me, from a CSP perspective, looks like
>>>>> quite a headache. In fact, I'd go as far as to suggest this
>>>>> communication should happen through an alternative channel, such as
>>>>> vsock, having a proxy on the Host, but I guess that depends on the CSP
>>>>> infrastructure.
>>>>
>>>> If we have an alternative channel (vsock?) and a proxy on the host,
>>>> maybe we can share parts of the solution between SEV and SNP.
>>>>
>>>>
>>>>> For SEV/SEV-ES, as the attestation happens at the VMM level, there's
>>>>> still the need to have some interactions with it. As Tyler pointed
>>>>> out, we basically need to retrieve the measurement and, if valid,
>>>>> inject the secret. If the measurement isn't valid, the VM must be shut
>>>>> down immediately.
>>>>>
>>>>> In libkrun-tee, this operation is driven by the VMM in libkrun, which
>>>>> contacts the Attestation Server with the measurement and receives the
>>>>> secret in exchange. I guess for QEMU/libvirt we expect this to be
>>>>> driven by the upper management layer through a delegated component in
>>>>> the Host, such as NOVA. In this case, NOVA would need to:
>>>>>
>>>>> - Based on the upper management layer info and the Host properties,
>>>>> generate a guest policy and use it while generating the compute
>>>>> instance XML.
>>>>>
>>>>> - Ask libvirt to launch the VM.
>>>>
>>>> Launch the VM with -S (suspended; so it doesn't actually begin running
>>>> guest instructions).
>>>>
>>>>
>>>>>
>>>>> - Wait for the VM to be in SEV_STATE_LAUNCH_SECRET state *.
>>>>>
>>>>> - Retrieve the measurement *.
>>>>
>>>> Note that libvirt holds the QMP socket to QEMU. So whoever fetches the
>>>> measurement needs either (a) to ask libvirt to it; or (b) to connect to
>>>> another QMP listening socket for getting the measurement and injecting
>>>> the secret.
>>>
>>> Libvirt would not be particularly happy with allowing (b) because it
>>> enables the 3rd parties to change the VM state behind libvirt's back
>>> in ways that can ultimately confuse its understanding of the state
>>> of the VM. If there's some task that needs interaction with a QEMU
>>> managed by libvirt, we need to expose suitable APIs in libvirt (if
>>> they don't already exist).
>>>
>>>
>>> Regards,
>>> Daniel
>>>
^ permalink raw reply [flat|nested] 26+ messages in thread
* Re: SEV guest attestation
2021-11-25 12:44 ` Dov Murik
2021-11-25 13:42 ` Daniel P. Berrangé
@ 2021-11-25 15:11 ` Sergio Lopez
2021-11-25 15:40 ` Dr. David Alan Gilbert
1 sibling, 1 reply; 26+ messages in thread
From: Sergio Lopez @ 2021-11-25 15:11 UTC (permalink / raw)
To: Dov Murik
Cc: Daniel P. Berrangé, afrosi, James Bottomley,
Dr. David Alan Gilbert, qemu-devel, Hubertus Franke,
Tyler Fanelli, Tobin Feldman-Fitzthum, Jim Cadden, dinechin,
John Ferlan
[-- Attachment #1: Type: text/plain, Size: 5757 bytes --]
On Thu, Nov 25, 2021 at 02:44:51PM +0200, Dov Murik wrote:
> [+cc jejb, tobin, jim, hubertus]
>
>
> On 25/11/2021 9:14, Sergio Lopez wrote:
> > On Wed, Nov 24, 2021 at 06:29:07PM +0000, Dr. David Alan Gilbert wrote:
> >> * Daniel P. Berrangé (berrange@redhat.com) wrote:
> >>> On Wed, Nov 24, 2021 at 11:34:16AM -0500, Tyler Fanelli wrote:
> >>>> Hi,
> >>>>
> >>>> We recently discussed a way for remote SEV guest attestation through QEMU.
> >>>> My initial approach was to get data needed for attestation through different
> >>>> QMP commands (all of which are already available, so no changes required
> >>>> there), deriving hashes and certificate data; and collecting all of this
> >>>> into a new QMP struct (SevLaunchStart, which would include the VM's policy,
> >>>> secret, and GPA) which would need to be upstreamed into QEMU. Once this is
> >>>> provided, QEMU would then need to have support for attestation before a VM
> >>>> is started. Upon speaking to Dave about this proposal, he mentioned that
> >>>> this may not be the best approach, as some situations would render the
> >>>> attestation unavailable, such as the instance where a VM is running in a
> >>>> cloud, and a guest owner would like to perform attestation via QMP (a likely
> >>>> scenario), yet a cloud provider cannot simply let anyone pass arbitrary QMP
> >>>> commands, as this could be an issue.
> >>>
> >>> As a general point, QMP is a low level QEMU implementation detail,
> >>> which is generally expected to be consumed exclusively on the host
> >>> by a privileged mgmt layer, which will in turn expose its own higher
> >>> level APIs to users or other apps. I would not expect to see QMP
> >>> exposed to anything outside of the privileged host layer.
> >>>
> >>> We also use the QAPI protocol for QEMU guest agent commmunication,
> >>> however, that is a distinct service from QMP on the host. It shares
> >>> most infra with QMP but has a completely diffent command set. On the
> >>> host it is not consumed inside QEMU, but instead consumed by a
> >>> mgmt app like libvirt.
> >>>
> >>>> So I ask, does anyone involved in QEMU's SEV implementation have any input
> >>>> on a quality way to perform guest attestation? If so, I'd be interested.
> >>>
> >>> I think what's missing is some clearer illustrations of how this
> >>> feature is expected to be consumed in some real world application
> >>> and the use cases we're trying to solve.
> >>>
> >>> I'd like to understand how it should fit in with common libvirt
> >>> applications across the different virtualization management
> >>> scenarios - eg virsh (command line), virt-manger (local desktop
> >>> GUI), cockpit (single host web mgmt), OpenStack (cloud mgmt), etc.
> >>> And of course any non-traditional virt use cases that might be
> >>> relevant such as Kata.
> >>
> >> That's still not that clear; I know Alice and Sergio have some ideas
> >> (cc'd).
> >> There's also some standardisation efforts (e.g. https://www.potaroo.net/ietf/html/ids-wg-rats.html
> >> and https://www.ietf.org/archive/id/draft-ietf-rats-architecture-00.html
> >> ) - that I can't claim to fully understand.
> >> However, there are some themes that are emerging:
> >>
> >> a) One use is to only allow a VM to access some private data once we
> >> prove it's the VM we expect running in a secure/confidential system
> >> b) (a) normally involves requesting some proof from the VM and then
> >> providing it some confidential data/a key if it's OK
> >> c) RATs splits the problem up:
> >> https://www.ietf.org/archive/id/draft-ietf-rats-architecture-00.html#name-architectural-overview
> >> I don't fully understand the split yet, but in principal there are
> >> at least a few different things:
> >>
> >> d) The comms layer
> >> e) Something that validates the attestation message (i.e. the
> >> signatures are valid, the hashes all add up etc)
> >> f) Something that knows what hashes to expect (i.e. oh that's a RHEL
> >> 8.4 kernel, or that's a valid kernel command line)
> >> g) Something that holds some secrets that can be handed out if e & f
> >> are happy.
> >>
> >> There have also been proposals (e.g. Intel HTTPA) for an attestable
> >> connection after a VM is running; that's probably quite different from
> >> (g) but still involves (e) & (f).
> >>
> >> In the simpler setups d,e,f,g probably live in one place; but it's not
> >> clear where they live - for example one scenario says that your cloud
> >> management layer holds some of them, another says you don't trust your
> >> cloud management layer and you keep them separate.
> >>
> >> So I think all we're actually interested in at the moment, is (d) and
> >> (e) and the way for (g) to get the secret back to the guest.
> >>
> >> Unfortunately the comms and the contents of them varies heavily with
> >> technology; in some you're talking to the qemu/hypervisor (SEV/SEV-ES)
> >> while in some you're talking to the guest after boot (SEV-SNP/TDX maybe
> >> SEV-ES in some cases).
>
> SEV-ES has pre-launch measurement and secret injection, just like SEV
> (except that the measurement includes the initial states of all vcpus,
> that is, their VMSAs. BTW that means that in order to calculate the
> measurement the Attestation Server must know exactly how many vcpus are
> in the VM).
You need the number of vCPUs and an idea of what their initial state
is going to be, to be able to reproduce the same VMSA struct in the
Attestation Server.
This may tie the Attestation Server with a particular version of both
QEMU and KVM. I haven't checked if configuration changes in QEMU may
also have an impact on it.
Sergio.
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ permalink raw reply [flat|nested] 26+ messages in thread
* Re: SEV guest attestation
2021-11-25 15:11 ` Sergio Lopez
@ 2021-11-25 15:40 ` Dr. David Alan Gilbert
2021-11-25 15:56 ` Daniel P. Berrangé
0 siblings, 1 reply; 26+ messages in thread
From: Dr. David Alan Gilbert @ 2021-11-25 15:40 UTC (permalink / raw)
To: Sergio Lopez
Cc: Daniel P. Berrangé, Hubertus Franke, afrosi, James Bottomley,
qemu-devel, Dov Murik, Tyler Fanelli, Tobin Feldman-Fitzthum,
Jim Cadden, dinechin, John Ferlan
* Sergio Lopez (slp@redhat.com) wrote:
> On Thu, Nov 25, 2021 at 02:44:51PM +0200, Dov Murik wrote:
> > [+cc jejb, tobin, jim, hubertus]
> >
> >
> > On 25/11/2021 9:14, Sergio Lopez wrote:
> > > On Wed, Nov 24, 2021 at 06:29:07PM +0000, Dr. David Alan Gilbert wrote:
> > >> * Daniel P. Berrangé (berrange@redhat.com) wrote:
> > >>> On Wed, Nov 24, 2021 at 11:34:16AM -0500, Tyler Fanelli wrote:
> > >>>> Hi,
> > >>>>
> > >>>> We recently discussed a way for remote SEV guest attestation through QEMU.
> > >>>> My initial approach was to get data needed for attestation through different
> > >>>> QMP commands (all of which are already available, so no changes required
> > >>>> there), deriving hashes and certificate data; and collecting all of this
> > >>>> into a new QMP struct (SevLaunchStart, which would include the VM's policy,
> > >>>> secret, and GPA) which would need to be upstreamed into QEMU. Once this is
> > >>>> provided, QEMU would then need to have support for attestation before a VM
> > >>>> is started. Upon speaking to Dave about this proposal, he mentioned that
> > >>>> this may not be the best approach, as some situations would render the
> > >>>> attestation unavailable, such as the instance where a VM is running in a
> > >>>> cloud, and a guest owner would like to perform attestation via QMP (a likely
> > >>>> scenario), yet a cloud provider cannot simply let anyone pass arbitrary QMP
> > >>>> commands, as this could be an issue.
> > >>>
> > >>> As a general point, QMP is a low level QEMU implementation detail,
> > >>> which is generally expected to be consumed exclusively on the host
> > >>> by a privileged mgmt layer, which will in turn expose its own higher
> > >>> level APIs to users or other apps. I would not expect to see QMP
> > >>> exposed to anything outside of the privileged host layer.
> > >>>
> > >>> We also use the QAPI protocol for QEMU guest agent commmunication,
> > >>> however, that is a distinct service from QMP on the host. It shares
> > >>> most infra with QMP but has a completely diffent command set. On the
> > >>> host it is not consumed inside QEMU, but instead consumed by a
> > >>> mgmt app like libvirt.
> > >>>
> > >>>> So I ask, does anyone involved in QEMU's SEV implementation have any input
> > >>>> on a quality way to perform guest attestation? If so, I'd be interested.
> > >>>
> > >>> I think what's missing is some clearer illustrations of how this
> > >>> feature is expected to be consumed in some real world application
> > >>> and the use cases we're trying to solve.
> > >>>
> > >>> I'd like to understand how it should fit in with common libvirt
> > >>> applications across the different virtualization management
> > >>> scenarios - eg virsh (command line), virt-manger (local desktop
> > >>> GUI), cockpit (single host web mgmt), OpenStack (cloud mgmt), etc.
> > >>> And of course any non-traditional virt use cases that might be
> > >>> relevant such as Kata.
> > >>
> > >> That's still not that clear; I know Alice and Sergio have some ideas
> > >> (cc'd).
> > >> There's also some standardisation efforts (e.g. https://www.potaroo.net/ietf/html/ids-wg-rats.html
> > >> and https://www.ietf.org/archive/id/draft-ietf-rats-architecture-00.html
> > >> ) - that I can't claim to fully understand.
> > >> However, there are some themes that are emerging:
> > >>
> > >> a) One use is to only allow a VM to access some private data once we
> > >> prove it's the VM we expect running in a secure/confidential system
> > >> b) (a) normally involves requesting some proof from the VM and then
> > >> providing it some confidential data/a key if it's OK
> > >> c) RATs splits the problem up:
> > >> https://www.ietf.org/archive/id/draft-ietf-rats-architecture-00.html#name-architectural-overview
> > >> I don't fully understand the split yet, but in principal there are
> > >> at least a few different things:
> > >>
> > >> d) The comms layer
> > >> e) Something that validates the attestation message (i.e. the
> > >> signatures are valid, the hashes all add up etc)
> > >> f) Something that knows what hashes to expect (i.e. oh that's a RHEL
> > >> 8.4 kernel, or that's a valid kernel command line)
> > >> g) Something that holds some secrets that can be handed out if e & f
> > >> are happy.
> > >>
> > >> There have also been proposals (e.g. Intel HTTPA) for an attestable
> > >> connection after a VM is running; that's probably quite different from
> > >> (g) but still involves (e) & (f).
> > >>
> > >> In the simpler setups d,e,f,g probably live in one place; but it's not
> > >> clear where they live - for example one scenario says that your cloud
> > >> management layer holds some of them, another says you don't trust your
> > >> cloud management layer and you keep them separate.
> > >>
> > >> So I think all we're actually interested in at the moment, is (d) and
> > >> (e) and the way for (g) to get the secret back to the guest.
> > >>
> > >> Unfortunately the comms and the contents of them varies heavily with
> > >> technology; in some you're talking to the qemu/hypervisor (SEV/SEV-ES)
> > >> while in some you're talking to the guest after boot (SEV-SNP/TDX maybe
> > >> SEV-ES in some cases).
> >
> > SEV-ES has pre-launch measurement and secret injection, just like SEV
> > (except that the measurement includes the initial states of all vcpus,
> > that is, their VMSAs. BTW that means that in order to calculate the
> > measurement the Attestation Server must know exactly how many vcpus are
> > in the VM).
>
> You need the number of vCPUs and an idea of what their initial state
> is going to be, to be able to reproduce the same VMSA struct in the
> Attestation Server.
>
> This may tie the Attestation Server with a particular version of both
> QEMU and KVM. I haven't checked if configuration changes in QEMU may
> also have an impact on it.
That's all OK; I'm expecting the attestation server to be given a whole
pile of information about the apparent environment to check.
Dave
> Sergio.
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
^ permalink raw reply [flat|nested] 26+ messages in thread
* Re: SEV guest attestation
2021-11-25 15:40 ` Dr. David Alan Gilbert
@ 2021-11-25 15:56 ` Daniel P. Berrangé
2021-11-25 16:08 ` Dr. David Alan Gilbert
0 siblings, 1 reply; 26+ messages in thread
From: Daniel P. Berrangé @ 2021-11-25 15:56 UTC (permalink / raw)
To: Dr. David Alan Gilbert
Cc: Hubertus Franke, Sergio Lopez, afrosi, James Bottomley,
qemu-devel, Dov Murik, Tyler Fanelli, Tobin Feldman-Fitzthum,
Jim Cadden, dinechin, John Ferlan
On Thu, Nov 25, 2021 at 03:40:36PM +0000, Dr. David Alan Gilbert wrote:
> * Sergio Lopez (slp@redhat.com) wrote:
> > On Thu, Nov 25, 2021 at 02:44:51PM +0200, Dov Murik wrote:
> > >
> > > SEV-ES has pre-launch measurement and secret injection, just like SEV
> > > (except that the measurement includes the initial states of all vcpus,
> > > that is, their VMSAs. BTW that means that in order to calculate the
> > > measurement the Attestation Server must know exactly how many vcpus are
> > > in the VM).
> >
> > You need the number of vCPUs and an idea of what their initial state
> > is going to be, to be able to reproduce the same VMSA struct in the
> > Attestation Server.
> >
> > This may tie the Attestation Server with a particular version of both
> > QEMU and KVM. I haven't checked if configuration changes in QEMU may
> > also have an impact on it.
>
> That's all OK; I'm expecting the attestation server to be given a whole
> pile of information about the apparent environment to check.
Generally though we try not to let a VM to tied to a specific
version of software. eg use machine types to ensure that the
guest can run on any QEMU version, and get the same environment.
This lets host admin upgrade the host software for bug/security
fixes without negatively impacting users. It'd be nice not to
loose that feature with SEV if possible.
IOW, if there are aspects of the vCPU initial state that might
vary over time with different QEMU versions, should we be looking
to tie that variance into the machine type version.
For KVM changes, this might again come back to the idea fo a
"host type version".
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 :|
^ permalink raw reply [flat|nested] 26+ messages in thread
* Re: SEV guest attestation
2021-11-25 15:56 ` Daniel P. Berrangé
@ 2021-11-25 16:08 ` Dr. David Alan Gilbert
2021-11-29 13:33 ` Dov Murik
0 siblings, 1 reply; 26+ messages in thread
From: Dr. David Alan Gilbert @ 2021-11-25 16:08 UTC (permalink / raw)
To: Daniel P. Berrangé
Cc: Hubertus Franke, Sergio Lopez, afrosi, James Bottomley,
qemu-devel, Dov Murik, Tyler Fanelli, Tobin Feldman-Fitzthum,
Jim Cadden, dinechin, John Ferlan
* Daniel P. Berrangé (berrange@redhat.com) wrote:
> On Thu, Nov 25, 2021 at 03:40:36PM +0000, Dr. David Alan Gilbert wrote:
> > * Sergio Lopez (slp@redhat.com) wrote:
> > > On Thu, Nov 25, 2021 at 02:44:51PM +0200, Dov Murik wrote:
> > > >
> > > > SEV-ES has pre-launch measurement and secret injection, just like SEV
> > > > (except that the measurement includes the initial states of all vcpus,
> > > > that is, their VMSAs. BTW that means that in order to calculate the
> > > > measurement the Attestation Server must know exactly how many vcpus are
> > > > in the VM).
> > >
> > > You need the number of vCPUs and an idea of what their initial state
> > > is going to be, to be able to reproduce the same VMSA struct in the
> > > Attestation Server.
> > >
> > > This may tie the Attestation Server with a particular version of both
> > > QEMU and KVM. I haven't checked if configuration changes in QEMU may
> > > also have an impact on it.
> >
> > That's all OK; I'm expecting the attestation server to be given a whole
> > pile of information about the apparent environment to check.
>
> Generally though we try not to let a VM to tied to a specific
> version of software. eg use machine types to ensure that the
> guest can run on any QEMU version, and get the same environment.
> This lets host admin upgrade the host software for bug/security
> fixes without negatively impacting users. It'd be nice not to
> loose that feature with SEV if possible.
>
> IOW, if there are aspects of the vCPU initial state that might
> vary over time with different QEMU versions, should we be looking
> to tie that variance into the machine type version.
It's not tied to a particular version; but you may need to let the
attesting server know what version it's using so that it can check
everything adds up.
Dave
> For KVM changes, this might again come back to the idea fo a
> "host type version".
>
> 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 :|
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
^ permalink raw reply [flat|nested] 26+ messages in thread
* Re: SEV guest attestation
2021-11-25 16:08 ` Dr. David Alan Gilbert
@ 2021-11-29 13:33 ` Dov Murik
0 siblings, 0 replies; 26+ messages in thread
From: Dov Murik @ 2021-11-29 13:33 UTC (permalink / raw)
To: Dr. David Alan Gilbert, Daniel P. Berrangé
Cc: Dov Murik, Sergio Lopez, afrosi, James Bottomley, qemu-devel,
Hubertus Franke, Tyler Fanelli, Tobin Feldman-Fitzthum,
Jim Cadden, dinechin, John Ferlan
On 25/11/2021 18:08, Dr. David Alan Gilbert wrote:
> * Daniel P. Berrangé (berrange@redhat.com) wrote:
>> On Thu, Nov 25, 2021 at 03:40:36PM +0000, Dr. David Alan Gilbert wrote:
>>> * Sergio Lopez (slp@redhat.com) wrote:
>>>> On Thu, Nov 25, 2021 at 02:44:51PM +0200, Dov Murik wrote:
>>>>>
>>>>> SEV-ES has pre-launch measurement and secret injection, just like SEV
>>>>> (except that the measurement includes the initial states of all vcpus,
>>>>> that is, their VMSAs. BTW that means that in order to calculate the
>>>>> measurement the Attestation Server must know exactly how many vcpus are
>>>>> in the VM).
>>>>
>>>> You need the number of vCPUs and an idea of what their initial state
>>>> is going to be, to be able to reproduce the same VMSA struct in the
>>>> Attestation Server.
>>>>
>>>> This may tie the Attestation Server with a particular version of both
>>>> QEMU and KVM. I haven't checked if configuration changes in QEMU may
>>>> also have an impact on it.
>>>
>>> That's all OK; I'm expecting the attestation server to be given a whole
>>> pile of information about the apparent environment to check.
>>
>> Generally though we try not to let a VM to tied to a specific
>> version of software. eg use machine types to ensure that the
>> guest can run on any QEMU version, and get the same environment.
>> This lets host admin upgrade the host software for bug/security
>> fixes without negatively impacting users. It'd be nice not to
>> loose that feature with SEV if possible.
>>
>> IOW, if there are aspects of the vCPU initial state that might
>> vary over time with different QEMU versions, should we be looking
>> to tie that variance into the machine type version.
>
> It's not tied to a particular version; but you may need to let the
> attesting server know what version it's using so that it can check
> everything adds up.
To further complicate things, note that in SEV-ES the reset vector
address (CS:IP) for all APs is not set by QEMU, but taken from GUIDed
tables in OVMF (towards the end of the image); QEMU parses the table and
takes the reset address from there. So a benign-looking change in OVMF
(changing the AP reset vector address) might cause a change in the
VMSAs, and therefore a change in the measurement.
Of course the OVMF binary itself is part of the measurement as well.
-Dov
>
> Dave
>
>> For KVM changes, this might again come back to the idea fo a
>> "host type version".
>>
>> 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 :|
>>
^ permalink raw reply [flat|nested] 26+ messages in thread
* Re: SEV guest attestation
2021-11-25 7:14 ` Sergio Lopez
2021-11-25 12:44 ` Dov Murik
@ 2021-11-25 13:20 ` Dr. David Alan Gilbert
2021-11-25 13:36 ` Daniel P. Berrangé
2021-11-25 13:52 ` Daniel P. Berrangé
3 siblings, 0 replies; 26+ messages in thread
From: Dr. David Alan Gilbert @ 2021-11-25 13:20 UTC (permalink / raw)
To: Sergio Lopez
Cc: Daniel P. Berrangé, afrosi, qemu-devel, dovmurik,
Tyler Fanelli, dinechin, John Ferlan
* Sergio Lopez (slp@redhat.com) wrote:
> On Wed, Nov 24, 2021 at 06:29:07PM +0000, Dr. David Alan Gilbert wrote:
> > * Daniel P. Berrangé (berrange@redhat.com) wrote:
> > > On Wed, Nov 24, 2021 at 11:34:16AM -0500, Tyler Fanelli wrote:
> > > > Hi,
> > > >
> > > > We recently discussed a way for remote SEV guest attestation through QEMU.
> > > > My initial approach was to get data needed for attestation through different
> > > > QMP commands (all of which are already available, so no changes required
> > > > there), deriving hashes and certificate data; and collecting all of this
> > > > into a new QMP struct (SevLaunchStart, which would include the VM's policy,
> > > > secret, and GPA) which would need to be upstreamed into QEMU. Once this is
> > > > provided, QEMU would then need to have support for attestation before a VM
> > > > is started. Upon speaking to Dave about this proposal, he mentioned that
> > > > this may not be the best approach, as some situations would render the
> > > > attestation unavailable, such as the instance where a VM is running in a
> > > > cloud, and a guest owner would like to perform attestation via QMP (a likely
> > > > scenario), yet a cloud provider cannot simply let anyone pass arbitrary QMP
> > > > commands, as this could be an issue.
> > >
> > > As a general point, QMP is a low level QEMU implementation detail,
> > > which is generally expected to be consumed exclusively on the host
> > > by a privileged mgmt layer, which will in turn expose its own higher
> > > level APIs to users or other apps. I would not expect to see QMP
> > > exposed to anything outside of the privileged host layer.
> > >
> > > We also use the QAPI protocol for QEMU guest agent commmunication,
> > > however, that is a distinct service from QMP on the host. It shares
> > > most infra with QMP but has a completely diffent command set. On the
> > > host it is not consumed inside QEMU, but instead consumed by a
> > > mgmt app like libvirt.
> > >
> > > > So I ask, does anyone involved in QEMU's SEV implementation have any input
> > > > on a quality way to perform guest attestation? If so, I'd be interested.
> > >
> > > I think what's missing is some clearer illustrations of how this
> > > feature is expected to be consumed in some real world application
> > > and the use cases we're trying to solve.
> > >
> > > I'd like to understand how it should fit in with common libvirt
> > > applications across the different virtualization management
> > > scenarios - eg virsh (command line), virt-manger (local desktop
> > > GUI), cockpit (single host web mgmt), OpenStack (cloud mgmt), etc.
> > > And of course any non-traditional virt use cases that might be
> > > relevant such as Kata.
> >
> > That's still not that clear; I know Alice and Sergio have some ideas
> > (cc'd).
> > There's also some standardisation efforts (e.g. https://www.potaroo.net/ietf/html/ids-wg-rats.html
> > and https://www.ietf.org/archive/id/draft-ietf-rats-architecture-00.html
> > ) - that I can't claim to fully understand.
> > However, there are some themes that are emerging:
> >
> > a) One use is to only allow a VM to access some private data once we
> > prove it's the VM we expect running in a secure/confidential system
> > b) (a) normally involves requesting some proof from the VM and then
> > providing it some confidential data/a key if it's OK
> > c) RATs splits the problem up:
> > https://www.ietf.org/archive/id/draft-ietf-rats-architecture-00.html#name-architectural-overview
> > I don't fully understand the split yet, but in principal there are
> > at least a few different things:
> >
> > d) The comms layer
> > e) Something that validates the attestation message (i.e. the
> > signatures are valid, the hashes all add up etc)
> > f) Something that knows what hashes to expect (i.e. oh that's a RHEL
> > 8.4 kernel, or that's a valid kernel command line)
> > g) Something that holds some secrets that can be handed out if e & f
> > are happy.
> >
> > There have also been proposals (e.g. Intel HTTPA) for an attestable
> > connection after a VM is running; that's probably quite different from
> > (g) but still involves (e) & (f).
> >
> > In the simpler setups d,e,f,g probably live in one place; but it's not
> > clear where they live - for example one scenario says that your cloud
> > management layer holds some of them, another says you don't trust your
> > cloud management layer and you keep them separate.
> >
> > So I think all we're actually interested in at the moment, is (d) and
> > (e) and the way for (g) to get the secret back to the guest.
> >
> > Unfortunately the comms and the contents of them varies heavily with
> > technology; in some you're talking to the qemu/hypervisor (SEV/SEV-ES)
> > while in some you're talking to the guest after boot (SEV-SNP/TDX maybe
> > SEV-ES in some cases).
> >
> > So my expectation at the moment is libvirt needs to provide a transport
> > layer for the comms, to enable an external validator to retrieve the
> > measurements from the guest/hypervisor and provide data back if
> > necessary. Once this shakes out a bit, we might want libvirt to be
> > able to invoke the validator; however I expect (f) and (g) to be much
> > more complex things that don't feel like they belong in libvirt.
>
> We experimented with the attestation flow quite a bit while working on
> SEV-ES support for libkrun-tee. One important aspect we noticed quite
> early, is that there's more data that's needed to be exchange of top
> of the attestation itself.
>
> For instance, even before you start the VM, the management layer in
> charge of coordinating the confidential VM launch needs to obtain the
> Virtualization TEE capabilities of the Host (SEV-ES vs. SEV-SNP
> vs. TDX) and the platform version, to know which features are
> available and whether that host is a candidate for running the VM at
> all.
> With that information, the mgmt layer can build a guest policy (this
> is SEV's terminology, but I guess we'll have something similar in
> TDX) and feed it to component launching the VMM (libvirt, in this
> case).
That's normal day-to-day business for something like libvirt?
>
> For SEV-SNP, this is pretty much the end of the story, because the
> attestation exchange is driven by an agent inside the guest. Well,
> there's also the need to have in the VM a well-known vNIC bridged to a
> network that's routed to the Attestation Server, that everyone seems
> to consider a given, but to me, from a CSP perspective, looks like
> quite a headache. In fact, I'd go as far as to suggest this
> communication should happen through an alternative channel, such as
> vsock, having a proxy on the Host, but I guess that depends on the CSP
> infrastructure.
Do we know if TDX describe the plans for this anywhere?
Again, maybe libvirt could be taught to wire that socket upto a proxy.
Also, which direction is the connection here - does the VM wait for the
attestor or does it ask to be attested?
> For SEV/SEV-ES, as the attestation happens at the VMM level, there's
> still the need to have some interactions with it. As Tyler pointed
> out, we basically need to retrieve the measurement and, if valid,
> inject the secret. If the measurement isn't valid, the VM must be shut
> down immediately.
>
> In libkrun-tee, this operation is driven by the VMM in libkrun, which
> contacts the Attestation Server with the measurement and receives the
> secret in exchange. I guess for QEMU/libvirt we expect this to be
> driven by the upper management layer through a delegated component in
> the Host, such as NOVA. In this case, NOVA would need to:
>
> - Based on the upper management layer info and the Host properties,
> generate a guest policy and use it while generating the compute
> instance XML.
>
> - Ask libvirt to launch the VM.
>
> - Wait for the VM to be in SEV_STATE_LAUNCH_SECRET state *.
>
> - Retrieve the measurement *.
>
> - Contact the Attestation Server and provide it with some kind of
> information to uniquely identify the VM (needed to determine what's
> the expected measurement) and the measurement itself.
>
> * If the measurement if valid, inject the secret *.
>
> + The secret is pre-encrypted with a key that only the PSP has,
> so there's no need to do any special handling of it.
>
> - Ask libvirt to either destroy the VM (if the measurement wasn't
> valid or there was some kind of communication error with the
> Attestation Server) or continue the execution of the VM (this will
> be the first time kvm_vcpu_run() is entered).
>
> The operations marked with (*) are the ones that I'm not sure if
> NOVA should communicate with libvirt or talk directly to QEMU.
My preference is for there to be a way to go via libvirt
Dave
> Sergio.
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
^ permalink raw reply [flat|nested] 26+ messages in thread
* Re: SEV guest attestation
2021-11-25 7:14 ` Sergio Lopez
2021-11-25 12:44 ` Dov Murik
2021-11-25 13:20 ` Dr. David Alan Gilbert
@ 2021-11-25 13:36 ` Daniel P. Berrangé
2021-11-25 13:52 ` Daniel P. Berrangé
3 siblings, 0 replies; 26+ messages in thread
From: Daniel P. Berrangé @ 2021-11-25 13:36 UTC (permalink / raw)
To: Sergio Lopez
Cc: afrosi, Dr. David Alan Gilbert, qemu-devel, dovmurik,
Tyler Fanelli, dinechin, John Ferlan
On Thu, Nov 25, 2021 at 08:14:28AM +0100, Sergio Lopez wrote:
> On Wed, Nov 24, 2021 at 06:29:07PM +0000, Dr. David Alan Gilbert wrote:
> > * Daniel P. Berrangé (berrange@redhat.com) wrote:
> > > On Wed, Nov 24, 2021 at 11:34:16AM -0500, Tyler Fanelli wrote:
> > > > Hi,
> > > >
> > > > We recently discussed a way for remote SEV guest attestation through QEMU.
> > > > My initial approach was to get data needed for attestation through different
> > > > QMP commands (all of which are already available, so no changes required
> > > > there), deriving hashes and certificate data; and collecting all of this
> > > > into a new QMP struct (SevLaunchStart, which would include the VM's policy,
> > > > secret, and GPA) which would need to be upstreamed into QEMU. Once this is
> > > > provided, QEMU would then need to have support for attestation before a VM
> > > > is started. Upon speaking to Dave about this proposal, he mentioned that
> > > > this may not be the best approach, as some situations would render the
> > > > attestation unavailable, such as the instance where a VM is running in a
> > > > cloud, and a guest owner would like to perform attestation via QMP (a likely
> > > > scenario), yet a cloud provider cannot simply let anyone pass arbitrary QMP
> > > > commands, as this could be an issue.
> > >
> > > As a general point, QMP is a low level QEMU implementation detail,
> > > which is generally expected to be consumed exclusively on the host
> > > by a privileged mgmt layer, which will in turn expose its own higher
> > > level APIs to users or other apps. I would not expect to see QMP
> > > exposed to anything outside of the privileged host layer.
> > >
> > > We also use the QAPI protocol for QEMU guest agent commmunication,
> > > however, that is a distinct service from QMP on the host. It shares
> > > most infra with QMP but has a completely diffent command set. On the
> > > host it is not consumed inside QEMU, but instead consumed by a
> > > mgmt app like libvirt.
> > >
> > > > So I ask, does anyone involved in QEMU's SEV implementation have any input
> > > > on a quality way to perform guest attestation? If so, I'd be interested.
> > >
> > > I think what's missing is some clearer illustrations of how this
> > > feature is expected to be consumed in some real world application
> > > and the use cases we're trying to solve.
> > >
> > > I'd like to understand how it should fit in with common libvirt
> > > applications across the different virtualization management
> > > scenarios - eg virsh (command line), virt-manger (local desktop
> > > GUI), cockpit (single host web mgmt), OpenStack (cloud mgmt), etc.
> > > And of course any non-traditional virt use cases that might be
> > > relevant such as Kata.
> >
> > That's still not that clear; I know Alice and Sergio have some ideas
> > (cc'd).
> > There's also some standardisation efforts (e.g. https://www.potaroo.net/ietf/html/ids-wg-rats.html
> > and https://www.ietf.org/archive/id/draft-ietf-rats-architecture-00.html
> > ) - that I can't claim to fully understand.
> > However, there are some themes that are emerging:
> >
> > a) One use is to only allow a VM to access some private data once we
> > prove it's the VM we expect running in a secure/confidential system
> > b) (a) normally involves requesting some proof from the VM and then
> > providing it some confidential data/a key if it's OK
> > c) RATs splits the problem up:
> > https://www.ietf.org/archive/id/draft-ietf-rats-architecture-00.html#name-architectural-overview
> > I don't fully understand the split yet, but in principal there are
> > at least a few different things:
> >
> > d) The comms layer
> > e) Something that validates the attestation message (i.e. the
> > signatures are valid, the hashes all add up etc)
> > f) Something that knows what hashes to expect (i.e. oh that's a RHEL
> > 8.4 kernel, or that's a valid kernel command line)
> > g) Something that holds some secrets that can be handed out if e & f
> > are happy.
> >
> > There have also been proposals (e.g. Intel HTTPA) for an attestable
> > connection after a VM is running; that's probably quite different from
> > (g) but still involves (e) & (f).
> >
> > In the simpler setups d,e,f,g probably live in one place; but it's not
> > clear where they live - for example one scenario says that your cloud
> > management layer holds some of them, another says you don't trust your
> > cloud management layer and you keep them separate.
> >
> > So I think all we're actually interested in at the moment, is (d) and
> > (e) and the way for (g) to get the secret back to the guest.
> >
> > Unfortunately the comms and the contents of them varies heavily with
> > technology; in some you're talking to the qemu/hypervisor (SEV/SEV-ES)
> > while in some you're talking to the guest after boot (SEV-SNP/TDX maybe
> > SEV-ES in some cases).
> >
> > So my expectation at the moment is libvirt needs to provide a transport
> > layer for the comms, to enable an external validator to retrieve the
> > measurements from the guest/hypervisor and provide data back if
> > necessary. Once this shakes out a bit, we might want libvirt to be
> > able to invoke the validator; however I expect (f) and (g) to be much
> > more complex things that don't feel like they belong in libvirt.
>
> We experimented with the attestation flow quite a bit while working on
> SEV-ES support for libkrun-tee. One important aspect we noticed quite
> early, is that there's more data that's needed to be exchange of top
> of the attestation itself.
>
> For instance, even before you start the VM, the management layer in
> charge of coordinating the confidential VM launch needs to obtain the
> Virtualization TEE capabilities of the Host (SEV-ES vs. SEV-SNP
> vs. TDX) and the platform version, to know which features are
> available and whether that host is a candidate for running the VM at
> all.
Libvirt already reports a wide variety of information about a
compute host, that is used for placement decisions by mgmt apps,
and this includes SEV data (obtained from qemu's query-sev-capabilities)
> With that information, the mgmt layer can build a guest policy (this
> is SEV's terminology, but I guess we'll have something similar in
> TDX) and feed it to component launching the VMM (libvirt, in this
> case).
>
> For SEV-SNP, this is pretty much the end of the story, because the
> attestation exchange is driven by an agent inside the guest. Well,
> there's also the need to have in the VM a well-known vNIC bridged to a
> network that's routed to the Attestation Server, that everyone seems
> to consider a given, but to me, from a CSP perspective, looks like
> quite a headache. In fact, I'd go as far as to suggest this
> communication should happen through an alternative channel, such as
> vsock, having a proxy on the Host, but I guess that depends on the CSP
> infrastructure.
>
> For SEV/SEV-ES, as the attestation happens at the VMM level, there's
> still the need to have some interactions with it. As Tyler pointed
> out, we basically need to retrieve the measurement and, if valid,
> inject the secret. If the measurement isn't valid, the VM must be shut
> down immediately.
Is that really 'must' be shut down or merely 'should' be shut down.
I'm expecting the latter, as if we're faced with an untrustworthy
compute host, we can't guarantee it will ever be shut dwon.
>
> In libkrun-tee, this operation is driven by the VMM in libkrun, which
> contacts the Attestation Server with the measurement and receives the
> secret in exchange. I guess for QEMU/libvirt we expect this to be
> driven by the upper management layer through a delegated component in
> the Host, such as NOVA. In this case, NOVA would need to:
>
> - Based on the upper management layer info and the Host properties,
> generate a guest policy and use it while generating the compute
> instance XML.
>
> - Ask libvirt to launch the VM.
>
> - Wait for the VM to be in SEV_STATE_LAUNCH_SECRET state *.
>
> - Retrieve the measurement *.
>
> - Contact the Attestation Server and provide it with some kind of
> information to uniquely identify the VM (needed to determine what's
> the expected measurement) and the measurement itself.
>
> * If the measurement if valid, inject the secret *.
>
> + The secret is pre-encrypted with a key that only the PSP has,
> so there's no need to do any special handling of it.
>
> - Ask libvirt to either destroy the VM (if the measurement wasn't
> valid or there was some kind of communication error with the
> Attestation Server) or continue the execution of the VM (this will
> be the first time kvm_vcpu_run() is entered).
>
> The operations marked with (*) are the ones that I'm not sure if
> NOVA should communicate with libvirt or talk directly to QEMU.
Nova must always talk with libvirt, never QEMU, because it needs to
be insulated from low level implementation details that change over
time. The QEMU binary we are invoking today, might be completely
replaced with something new tomorrow, with totally different CLI /
APIs, and livirt will isolate apps from this.
Also we need to bear in mind the complexity we're putting on users
and mgmt apps.
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 :|
^ permalink raw reply [flat|nested] 26+ messages in thread
* Re: SEV guest attestation
2021-11-25 7:14 ` Sergio Lopez
` (2 preceding siblings ...)
2021-11-25 13:36 ` Daniel P. Berrangé
@ 2021-11-25 13:52 ` Daniel P. Berrangé
2021-11-25 13:55 ` Dov Murik
2021-11-25 15:00 ` Dr. David Alan Gilbert
3 siblings, 2 replies; 26+ messages in thread
From: Daniel P. Berrangé @ 2021-11-25 13:52 UTC (permalink / raw)
To: Sergio Lopez
Cc: afrosi, Dr. David Alan Gilbert, qemu-devel, dovmurik,
Tyler Fanelli, dinechin, John Ferlan
On Thu, Nov 25, 2021 at 08:14:28AM +0100, Sergio Lopez wrote:
> For SEV-SNP, this is pretty much the end of the story, because the
> attestation exchange is driven by an agent inside the guest. Well,
> there's also the need to have in the VM a well-known vNIC bridged to a
> network that's routed to the Attestation Server, that everyone seems
> to consider a given, but to me, from a CSP perspective, looks like
> quite a headache. In fact, I'd go as far as to suggest this
> communication should happen through an alternative channel, such as
> vsock, having a proxy on the Host, but I guess that depends on the CSP
> infrastructure.
Allowing network connections from inside the VM, to any kind
of host side mgmt LAN services is a big no for some cloud hosts.
They usually desire for any guest network connectivity to be
associated with a VLAN/network segment that is strictly isolated
from any host mgmt LAN.
OpenStack provides a virtual CCDROM for injecting cloud-init
metadata as an alternative to the network based metadata REST
service, since they latter often isn't deployed.
Similarly for virtual filesystems, we've designed virtiofs,
rather than relying on a 2nd NIC combined with NFS.
We cannot assume availability of a real network device for the
attestation. If one does exist fine, but there needs to be an
alternative option that can be used.
On a slightly different topic - if the attestation is driven
from an agent inside the guest, this seems to imply we let the
guest vCPUs start beforre attestation is done. Contrary to
the SEV/SEV-ES where we seem to be wanting vCPUs to remain
in the stopped state until attestation is complete & secrets
provided. If the vCPUs are started, is there some mechanism
to restrict what can be done before attestation is complete?
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 :|
^ permalink raw reply [flat|nested] 26+ messages in thread* Re: SEV guest attestation
2021-11-25 13:52 ` Daniel P. Berrangé
@ 2021-11-25 13:55 ` Dov Murik
2021-11-25 15:00 ` Dr. David Alan Gilbert
1 sibling, 0 replies; 26+ messages in thread
From: Dov Murik @ 2021-11-25 13:55 UTC (permalink / raw)
To: Daniel P. Berrangé, Sergio Lopez
Cc: afrosi, James Bottomley, Dr. David Alan Gilbert, qemu-devel,
Dov Murik, Tyler Fanelli, dinechin, John Ferlan
On 25/11/2021 15:52, Daniel P. Berrangé wrote:
> On Thu, Nov 25, 2021 at 08:14:28AM +0100, Sergio Lopez wrote:
>> For SEV-SNP, this is pretty much the end of the story, because the
>> attestation exchange is driven by an agent inside the guest. Well,
>> there's also the need to have in the VM a well-known vNIC bridged to a
>> network that's routed to the Attestation Server, that everyone seems
>> to consider a given, but to me, from a CSP perspective, looks like
>> quite a headache. In fact, I'd go as far as to suggest this
>> communication should happen through an alternative channel, such as
>> vsock, having a proxy on the Host, but I guess that depends on the CSP
>> infrastructure.
>
> Allowing network connections from inside the VM, to any kind
> of host side mgmt LAN services is a big no for some cloud hosts.
>
> They usually desire for any guest network connectivity to be
> associated with a VLAN/network segment that is strictly isolated
> from any host mgmt LAN.
>
> OpenStack provides a virtual CCDROM for injecting cloud-init
> metadata as an alternative to the network based metadata REST
> service, since they latter often isn't deployed.
>
> Similarly for virtual filesystems, we've designed virtiofs,
> rather than relying on a 2nd NIC combined with NFS.
>
> We cannot assume availability of a real network device for the
> attestation. If one does exist fine, but there needs to be an
> alternative option that can be used.
>
>
> On a slightly different topic - if the attestation is driven
> from an agent inside the guest, this seems to imply we let the
> guest vCPUs start beforre attestation is done. Contrary to
> the SEV/SEV-ES where we seem to be wanting vCPUs to remain
> in the stopped state until attestation is complete & secrets
> provided. If the vCPUs are started, is there some mechanism
> to restrict what can be done before attestation is complete?
The only mechanism is to design the workload in the Guest in a way that
it can't do anything meaningful until the secret is injected, and the
Attestation Server will release the secret only if a proper attestation
report is presented.
James (cc'd) wants to move this attestation check as early as possible
--> "to restrict what can be done before attestation is complete".
-Dov
^ permalink raw reply [flat|nested] 26+ messages in thread
* Re: SEV guest attestation
2021-11-25 13:52 ` Daniel P. Berrangé
2021-11-25 13:55 ` Dov Murik
@ 2021-11-25 15:00 ` Dr. David Alan Gilbert
1 sibling, 0 replies; 26+ messages in thread
From: Dr. David Alan Gilbert @ 2021-11-25 15:00 UTC (permalink / raw)
To: Daniel P. Berrangé
Cc: Sergio Lopez, afrosi, qemu-devel, dovmurik, Tyler Fanelli,
dinechin, John Ferlan
* Daniel P. Berrangé (berrange@redhat.com) wrote:
> On Thu, Nov 25, 2021 at 08:14:28AM +0100, Sergio Lopez wrote:
> > For SEV-SNP, this is pretty much the end of the story, because the
> > attestation exchange is driven by an agent inside the guest. Well,
> > there's also the need to have in the VM a well-known vNIC bridged to a
> > network that's routed to the Attestation Server, that everyone seems
> > to consider a given, but to me, from a CSP perspective, looks like
> > quite a headache. In fact, I'd go as far as to suggest this
> > communication should happen through an alternative channel, such as
> > vsock, having a proxy on the Host, but I guess that depends on the CSP
> > infrastructure.
>
> Allowing network connections from inside the VM, to any kind
> of host side mgmt LAN services is a big no for some cloud hosts.
>
> They usually desire for any guest network connectivity to be
> associated with a VLAN/network segment that is strictly isolated
> from any host mgmt LAN.
>
> OpenStack provides a virtual CCDROM for injecting cloud-init
> metadata as an alternative to the network based metadata REST
> service, since they latter often isn't deployed.
>
> Similarly for virtual filesystems, we've designed virtiofs,
> rather than relying on a 2nd NIC combined with NFS.
>
> We cannot assume availability of a real network device for the
> attestation. If one does exist fine, but there needs to be an
> alternative option that can be used.
>
>
> On a slightly different topic - if the attestation is driven
> from an agent inside the guest, this seems to imply we let the
> guest vCPUs start beforre attestation is done. Contrary to
> the SEV/SEV-ES where we seem to be wanting vCPUs to remain
> in the stopped state until attestation is complete & secrets
> provided.
That's right; SEV/SEV-ES is the odd case here.
> If the vCPUs are started, is there some mechanism
> to restrict what can be done before attestation is complete?
Just the fact you haven't provided it the keys to decrypt it's disk to
do anything interesting; there's the potential to add extra if you
wanted (e.g. 802.1X network auth).
Dave
>
> 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 :|
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
^ permalink raw reply [flat|nested] 26+ messages in thread