libvirt: AMD SEV-ES support
Still WIP. Should be resubmitted to 2024.2 once spec proposal is open. Change-Id: Ia18d836d77133b06439cc5f5471496d4ea6f6910
This commit is contained in:
Takashi Kajinami
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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=======================================================================
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libvirt driver launching instances with memory encryption by AMD SEV-ES
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=======================================================================
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https://blueprints.launchpad.net/nova/+spec/amd-sev-es-libvirt-support
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This spec proposes work required in order to extend the existing libvirt driver
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feature to launch AMD SEV-encrypted instances, to support also using AMD
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SEV-ES, which is the extended version of AMD SEV, as memory encryption
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mechanism.
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Problem description
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===================
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Current libvirt driver supports launching instances with memory encryption by
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`AMD's SEV (Secure Encrypted Virtualization) technology
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<https://developer.amd.com/sev/>`_. However the current implementation supports
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only AMD SEV, and does not support new versions. For exmaple SEV-ES also
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encrypts all CPU register contents when a VM stops running, to achieve more
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complete protection of VM data, but users can't leverage these features because
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of this limitation.
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.. note::
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At the time or writing AMD already released CPUs which supports SEV-SNP, but
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the required hypervisor features to use SEV-SNP are not yet merged into
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the underlying components(kernel, QEMU, libvirt and ovmf). So in this spec
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we focus on SEV-ES. We attempt to keep the proposal as much compatiblre with
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SEV-SNP as possible, based on the implementations published by AMD.
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Use Cases
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---------
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#. As a cloud administrator, in order that my users can have more confidence
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in the security of their running instances, I want to provide a flavor
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containing the `required trait extra spec
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<https://docs.openstack.org/nova/latest/user/flavors.html#extra-specs-required-traits>`_
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which will allow users booting instances with that flavor to ensure
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that their instances run on an SEV-ES-capable compute host with SEV-ES
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encryption, instead of SEV encryption, enabled.
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#. As a cloud user, in order to reduce data leakage risks further, I want to
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be able to boot VM instances with SEV-ES functionality, instead of SEV
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functionality, enabled.
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Proposed change
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===============
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We propose extending the existing implementation to support launching instances
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with SEV functionality.
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- Add detection of host SEV-ES capabilities, which checks the following items.
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- The presence of the following XML in the response from a libvirt
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`virConnectGetDomainCapabilities()
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<https://libvirt.org/html/libvirt-libvirt-domain.html#virConnectGetDomainCapabilities>`_
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API call `indicates that both QEMU and the AMD Secure Processor
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(AMD-SP) support SEV functionality
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<https://libvirt.org/git/?p=libvirt.git;a=commit;h=6688393c6b222b5d7cba238f21d55134611ede9c>`_::
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<domainCapabilities>
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...
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<features>
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...
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<sev supported='yes'/>
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...
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</sev>
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</features>
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</domainCapabilities>
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- ``/sys/module/kvm_amd/parameters/sev_es`` should have the value ``Y``
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to indicate that the kernel has SEV capabilities enabled. This
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should be readable by any user (i.e. even non-root).
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- Implement a new ``MEM_ENCRYPTION_CONTEXT_V2`` `resource class
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<https://specs.openstack.org/openstack/nova-specs/specs/mitaka/implemented/resource-classes.html>`_
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to represent the number of guests with SEV-ES enabled which a compute host
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can run concurrently. A separate resource class is required because maximum
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number of SEV-ES guests a compute host can accept is separate from maximum
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number of SEV guests.
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.. note::
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SEV and SEV-ES have separate limits of guest numbers, because SEV-ES
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requires SEV ASID while SEV does not. Maximum ASID should be configured in
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BIOS (or UEFI) to use SEV-ES. SEV-SNP requires ASID, so is expected to be
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able to use the same v2 class.
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- Add the new ``HW_CPU_AMD_SEV_ES`` trait to os-traits.
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- Make the libvirt driver `update the ProviderTree object
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<https://docs.openstack.org/nova/latest/reference/update-provider-tree.html>`_
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with the correct inventory for the new ``MEM_ENCRYPTION_CONTEXT_V2``
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resource class.
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- Change the libvirt driver to include extra XML in the guest's domain
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definition when ``resources:MEM_ENCRYPTION_CONTEXT_V2=1`` is present in
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the flavor extra specs. The extra XML is mostly similar to the one used in
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SEV, but its guest policy field needs the SEV-ES bit (bit 2) enabled.
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- Add support for a new ``hw:mem_encryption_mechanism`` parameter in flavor
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extra specs, and a new ``hw_mem_encryption_mecnahism`` image property. When
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either of these is set to ``amd-sev-es`` along with the parameter/propery to
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enable memory encryption, it would be internally translated to
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``resources:MEM_ENCRYPTION_CONTEXT_V2=1`` which would
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be added to the flavor extra specs in the ``RequestSpec`` object.
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if these new mechanism parameter/property is absent or set to ``amd-sev``
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then it would be translated to ``resources:MEM_ENCRYPTION_CONTEXT=1``.
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Alternatives
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------------
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None
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Data model impact
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-----------------
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A new resource class will be used to inventory slots for SEV-ES guests on
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SEV-ES-capable compute hosts.
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A new configuration option will be used (at least in the short term)
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to specify the maximum number of SEV-ES guests runnable on each compute
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host. This overrides the maximum number determined using the number exposed by
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libvirt API, in case the given limit is lower than the actual limit.
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REST API impact
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---------------
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None
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Security impact
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---------------
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None
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Notifications impact
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--------------------
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None
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Other end user impact
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---------------------
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The end user will harness SEV-ES through the existing mechanisms of
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resources in flavor extra specs and image properties.
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Performance Impact
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------------------
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No performance impact on nova is anticipated.
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Perfomance impact for the other parts are same as the existing SEV support
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feature.
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Other deployer impact
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---------------------
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In order for users to be able to use SEV-ES, the operator will need to
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perform the following steps:
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- Deploy SEV-ES-capable hardware as nova compute hosts.
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- Set maximum ASID in BIOS (or UEFI) to a value greater than 0.
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- Ensure that they have an appropriately configured software stack, so
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that the various layers are all SEV-ES ready:
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- kernel >= 4.16
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- QEMU >= 6.1.0
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- libvirt >= 4.5
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- ovmf >= commit 7f0b28415cb4 2020-08-12
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Finally, a cloud administrator will need to define SEV-ES-enabled flavors
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as described above, unless it is sufficient for users to define
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SEV-ES-enabled images.
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Developer impact
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----------------
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None
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Upgrade impact
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--------------
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None
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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kajinamit (irc: tkajinam)
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Other contributors:
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None
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Work Items
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----------
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Work items or tasks -- break the feature up into the things that need to be
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done to implement it. Those parts might end up being done by different people,
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but we're mostly trying to understand the timeline for implementation.
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Consider creating an ordering of patches, that allows gradually merging
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instead of the need to merge them all at once. For example if you are
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introducing a feature that requires implementation changes in multiple VM
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lifecycle operations then first add a step that rejects all the not yet
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supported actions with a HTTP 400 Bad Request. The error should explain that
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the <operation> is not supported with <feature> at this time. Then gradually
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remove the limitation as you progress with the implementation. This way we can
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merge your changes gradually and regardless when the feature freeze hit we can
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be sure that the system is consistent.
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Future work
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-----------
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None
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Dependencies
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============
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* Special hardware which supports SEV-ES for development, testing, and CI.
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* Recent versions of the hypervisor software stack which all support
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SEV-ES, as detailed in `Other deployer impact`_ above.
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Testing
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=======
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The ``fakelibvirt`` test driver will need adaptation to emulate
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SEV-ES-capable hardware.
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Corresponding unit/functional tests will need to be extended or added
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to cover:
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- detection of SEV-ES-capable hardware and software, e.g. perhaps as an
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extension of
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``nova.tests.functional.libvirt.test_report_cpu_traits.LibvirtReportTraitsTests``
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- the use of a trait to include extra SEV-specific libvirt domain XML
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configuration, e.g. within
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``nova.tests.unit.virt.libvirt.test_config``
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Documentation Impact
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====================
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- Update the entry in `the Feature Support Matrix
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<https://docs.openstack.org/nova/latest/user/support-matrix.html>`_,
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to explain now AMD SEV-ES is supported in addition to AMD SEV.
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- Update the existing `AMD SEV
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<https://docs.openstack.org/nova/latest/admin/sev.html>`_ guide to include
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information about SEV-ES>
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Other non-nova documentation should be updated too:
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- The `documentation for os-traits
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<https://docs.openstack.org/os-traits/latest/>`_ should be extended
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where appropriate.
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References
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==========
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- `AMD SEV landing page <https://developer.amd.com/sev>`_
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- `AMD SEV-KM API Specification
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<https://developer.amd.com/wp-content/resources/55766.PDF>`_
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- `AMD SEV github repository containing examples and tools
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<https://github.com/AMDESE/AMDSEV/>`_
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- `Slides from the 2017 Linux Security Summit describing SEV and
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preliminary performance results
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<http://events17.linuxfoundation.org/sites/events/files/slides/AMD%20SEV-ES.pdf>`_
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- `libvirt's SEV options <https://libvirt.org/formatdomain.html#sev>`_
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History
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=======
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.. list-table:: Revisions
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:header-rows: 1
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* - Release Name
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- Description
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* - 2024.2 Dalmetian
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- Introduced
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