[libvirt PATCH 00/12] tools: provide virt-qemu-sev-validate for SEV(-ES) launch attestation

Cole Robinson crobinso at redhat.com
Thu Oct 20 12:18:20 UTC 2022

On 10/18/22 5:22 AM, Daniel P. Berrangé wrote:
> On Sun, Oct 16, 2022 at 03:06:17PM -0400, Cole Robinson wrote:
>> On 10/7/22 7:42 AM, Daniel P. Berrangé wrote:
>>> The libvirt QEMU driver provides all the functionality required for
>>> launching a guest on AMD SEV(-ES) platforms, with a configuration
>>> that enables attestation of the launch measurement. The documentation
>>> for how to actually perform an attestation is severely lacking and
>>> not suitable for mere mortals to understand. IOW, someone trying to
>>> implement attestation is in for a world of pain and suffering.
>>> This series doesn't fix the documentation problem, but it does
>>> provide a reference implementation of a tool for performing
>>> attestation of SEV(-ES) guests in the context of libvirt / KVM.
>>> There will be other tools and libraries that implement attestation
>>> logic too, but this tool is likely somewhat unique in its usage of
>>> libvirt. Now for a attestation to be trustworthy you don't want to
>>> perform it on the hypervisor host, since the goal is to prove that
>>> the hypervisor has not acted maliciously. None the less it is still
>>> beneficial to have libvirt integration to some extent.
>>> When running this tool on a remote (trusted) host, it can connect
>>> to the libvirt hypervisor and fetch the data provided by the
>>> virDomainLaunchSecurityInfo API, which is safe to trust as the
>>> key pieces are cryptographically measured.
>>> Attestation is a complex problem though and it is very easy to
>>> screw up and feed the wrong information and then waste hours trying
>>> to figure out what piece was wrong, to cause the hash digest to
>>> change. For debugging such problems, you can thus tell the tool
>>> to operate insecurely, by querying libvirt for almost all of the
>>> configuration information required to determine the expected
>>> measurement. By comparing these results,to the results obtained
>>> in offline mode it helps narrow down where the mistake lies.
>>> So I view this tool as being useful in a number of ways:
>>>  * Quality assurance engineers needing to test libvirt/QEMU/KVM
>>>    get a simple and reliable tool for automating tests with.
>>>  * Users running simple libvirt deployments without any large
>>>    management stack, get a standalone tool for attestation
>>>    they can rely on.
>>>  * Developers writing/integrating attestation support into
>>>    management stacks above libvirt, get a reference against
>>>    which they can debug their own tools.
>>>  * Users wanting to demonstrate the core SEV/SEV-ES functionality
>>>    get a simple and reliable tool to illustrate the core concepts
>>>    involved.
>>> Since I didn't fancy writing such complex logic in C, this tool is
>>> a python3 program. As such, we don't want to include it in the
>>> main libvirt-client RPM, nor any other existing RPM. THus, this
>>> series puts it in a new libvirt-client-qemu RPM which, through no
>>> co-inicidence at all, is the same RPM I invented a few days ago to
>>> hold the virt-qemu-qmp-proxy command.
>>> Note, people will have already seen an earlier version of this
>>> tool I hacked up some months ago. This code is very significantly
>>> changed since that earlier version, to make it more maintainable,
>>> and simpler to use (especially for SEV-ES) but the general theme
>>> is still the same.
>>> Daniel P. Berrangé (12):
>>>   build-aux: only forbid gethostname in C files
>>>   tools: support validating SEV firmware boot measurements
>>>   tools: load guest config from libvirt
>>>   tools: support validating SEV direct kernel boot measurements
>>>   tools: load direct kernel config from libvirt
>>>   tools: support validating SEV-ES initial vCPU state measurements
>>>   tools: support automatically constructing SEV-ES vCPU state
>>>   tools: load CPU count and CPU SKU from libvirt
>>>   tools: support generating SEV secret injection tables
>>>   docs/kbase: describe attestation for SEV guests
>>>   scripts: add systemtap script for capturing SEV-ES VMSA
>>>   docs/manpages: add checklist of problems for SEV attestation
>> After the fix I mentioned on patch 7, the script worked for my sev,
>> sev-es, sev-es + kernel setup, with vmsa passed in and vmsa generated.
>> Attached is some pylint output, nothing really serious:
> We've not run pylint on libvirt tree historically, but I wonder
> if we should introduce it to check all our build scripts too.

Pylint needs a lot of hand holding. Every distro upgrade you'll hit new
issues, want to exclude more checks etc. I never looked into how
projects use it for CI gating, seems kinda exhausting unless you only
enable specific checks.

- Cole

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