libvirt: Stateless firmware support
NOTE: This will be submitted for reference and early discussions. This should be resubmitted to 2024.2 once spec proposal is open. blueprint: libvirt-stateless-firmware Change-Id: I3e3c2350e623a95e3b2831818012376df0508232
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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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libvit driver launching instances with stateless firmware
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=========================================================
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Since v8.6.0, libvirt allows launching instance with stateless firmware, which
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disables the potential attack serface from hypervisor. This work aims to
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introduce the required feature to allow users to use this feature.
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Problem description
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===================
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Libvirt v8.6.0 introduced the new feature to launch instance with stateless
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firmware. When an instance is launched with this feature enabled along with
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UEFI, the instance loads a single OVMF image which contains read-only CODE and
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VARS (or CODES only). This feature is useful for confidential computing use
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case, because it prevens injection into firmware vars from hypervisor. It also
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allows more complete measurement of elements involved in the boot chain of
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the instance which is the key requirement of remote attestation. This is
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described in `the libvirt guide
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<https://libvirt.org/kbase/launch_security_sev.html>`_ about SEV-encrypted
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guests.
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However this libvirt feature can't be enabled in instances launched by current
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nova, because nova does not set the required options in libvirt. Also nova
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always injects nvram file into libvirt domain XML.
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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 in
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the security of their running instances, I want to allow my users to
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enforce stateless firmware for their instances.
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#. As a user, I want to prevent risk caused by firmware variables injected by
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hypevisor, for instances which load very confidential data.
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Proposed change
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===============
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We propose adding a new image property to request stateless firmwre, so that
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users can create their instance with stateless firmware.
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- Add the new ``COMPUTE_SECURITY_STATELESS_FIRMWARE`` trait to os-traits.
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- Make libvirt driver check the current version of libvirt and report
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the ``supports_stateless_firmware`` capability when the version is equal or
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newer than v8.6.0. This capability should be mapped to
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the ``COMPUTE_SECURITY_STATELESS_FIRMWARE`` trait.
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- Add the new ``hw_firmware_stateless`` image property, which accept boolean
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values and is ``false`` by default. If the property is set to ``true`` then
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nova translate it to requiring the ``COMPUTE_SECURITY_STATELESS_FIRMWARE``
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trait.
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- Change the libvirt driver to adds the ``stateless`` option to the ``loader``
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element of libvirt domain XML, if instance metadata of the instance contains
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``hw_firmware_stateless`` property set to ``true``.
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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 trait and new image property will be used to present availability and
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request of stateless firmware feature in libvirt.
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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 be able to use statless firmware for their instances through
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the existing image property mechanism.
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Performance Impact
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------------------
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None
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Other deployer impact
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---------------------
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In order for users to be able to use this feature, the operator will need to
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deploy libvirt v8.6.0 or later in the deployment.
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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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#. Add the new ``COMPUTE_SECURITY_STATELESS_FIRMWARE`` trait to os-traits.
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#. Make libvirt driver check libvirt version and present availability of
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stateless firmware in compute node capabilities based on the detected
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version.
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#. Add the new ``hw_firmware_stateless`` image property to the ImageMeta
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object
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#. Update scheduler util to request ``COMPUTE_SECURITY_STATELESS_FIRMWARE``
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trait when the ``supports_stateless_firmware`` property in instance image
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properties is set to ``true``
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#. Make libvirt driver set ``stateless="yes"`` in the loder element when
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instance image properties contains the ``supports_stateless_firmware``
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property set to ``true``.
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#. Update documentations
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#. Update image property schema in glance to validate
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the new ``supports_stateless_firmware`` property.
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Unit tests and functional tests should be added according to new logic.
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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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Libvirt v8.6.0 or later.
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Testing
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=======
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The ``fakelibvirt`` test driver will need adaptation to emulate libvirt older
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than v8.6.0 and libvirt v8.6.0 or later.
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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 the statless firmware support by libvirt
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- the use of a trait to include extra stateless loader option in domain XML
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configuration.
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Documentation Impact
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====================
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- Update `the Feature Support Matrix
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<https://docs.openstack.org/nova/latest/user/support-matrix.html>`_, to
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include stateless firmware support.
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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 stateless firmware.
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References
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==========
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- `libvirt's Domain XML format
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<https://libvirt.org/formatdomain.html#bios-bootloader>`_
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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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