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The link was most likely broken when 'formatsecret' was converted to RST. Signed-off-by: Peter Krempa <pkrempa@redhat.com> Reviewed-by: Ján Tomko <jtomko@redhat.com>
140 lines
6.0 KiB
ReStructuredText
140 lines
6.0 KiB
ReStructuredText
.. role:: since
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====================================
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Storage volume encryption XML format
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====================================
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.. contents::
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Storage volume encryption XML
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-----------------------------
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Storage volumes may be encrypted, the XML snippet described below is used to
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represent the details of the encryption. It can be used as a part of a domain or
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storage configuration.
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The top-level tag of volume encryption specification is ``encryption``, with a
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mandatory attribute ``format``. Currently defined values of ``format`` are
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``default``, ``qcow``, ``luks``, and ``luks2``. Each value of ``format`` implies
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some expectations about the content of the ``encryption`` tag. Other format
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values may be defined in the future.
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The ``encryption`` tag supports an optional ``engine`` tag, which allows
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selecting which component actually handles the encryption. Currently defined
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values of ``engine`` are ``qemu`` and ``librbd``. Both ``qemu`` and ``librbd``
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require using the qemu driver. The ``librbd`` engine requires qemu version >=
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6.1.0, both ceph cluster and librbd1 >= 16.1.0, and is only applicable for RBD
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network disks. If the engine tag is not specified, the ``qemu`` engine will be
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used by default (assuming the qemu driver is used). Note that ``librbd`` engine
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is currently only supported by the qemu VM driver, and is not supported by the
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storage driver. Furthermore, the storage driver currently ignores the ``engine``
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tag.
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The ``encryption`` tag can currently contain a sequence of ``secret`` tags, each
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with mandatory attributes ``type`` and either ``uuid`` or ``usage`` (
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:since:`since 2.1.0` ). The only currently defined value of ``type`` is
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``volume``. The ``uuid`` is "uuid" of the ``secret`` while ``usage`` is the
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"usage" subelement field. A secret value can be set in libvirt by the
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`virSecretSetValue <html/libvirt-libvirt-secret.html#virSecretSetValue>`__ API.
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Alternatively, if supported by the particular volume format and driver,
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automatically generate a secret value at the time of volume creation, and store
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it using the specified ``uuid``.
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``qcow`` format
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~~~~~~~~~~~~~~~
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:since:`Since 4.5.0,` encryption formats ``default`` and ``qcow`` may no longer
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be used to create an encrypted volume. Usage of qcow encrypted volumes in QEMU
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began phasing out in QEMU 2.3 and by QEMU 2.9 creation of a qcow encrypted
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volume via qemu-img required usage of secret objects, but that support was not
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added to libvirt.
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``luks`` format
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~~~~~~~~~~~~~~~
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The ``luks`` format is specific to a luks encrypted volume and the secret is
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used in order to either encrypt during volume creation or decrypt the volume for
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usage by the domain. A single ``<secret type='passphrase'...>`` element is
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expected. :since:`Since 2.1.0` .
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For volume creation, it is possible to specify the encryption algorithm used to
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encrypt the luks volume. The following two optional elements may be provided for
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that purpose. It is hypervisor dependent as to which algorithms are supported.
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The default algorithm used by the storage driver backend when using qemu-img to
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create the volume is 'aes-256-cbc' using 'essiv' for initialization vector
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generation and 'sha256' hash algorithm for both the cipher and the
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initialization vector generation.
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``cipher``
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This element describes the cipher algorithm to be used to either encrypt or
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decrypt the luks volume. This element has the following attributes:
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``name``
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The name of the cipher algorithm used for data encryption, such as 'aes',
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'des', 'cast5', 'serpent', 'twofish', etc. Support of the specific
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algorithm is storage driver implementation dependent.
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``size``
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The size of the cipher in bits, such as '256', '192', '128', etc. Support
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of the specific size for a specific cipher is hypervisor dependent.
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``mode``
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An optional cipher algorithm mode such as 'cbc', 'xts', 'ecb', etc.
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Support of the specific cipher mode is hypervisor dependent.
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``hash``
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An optional master key hash algorithm such as 'md5', 'sha1', 'sha256',
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etc. Support of the specific hash algorithm is hypervisor dependent.
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``ivgen``
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This optional element describes the initialization vector generation
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algorithm used in conjunction with the ``cipher``. If the ``cipher`` is not
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provided, then an error will be generated by the parser.
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``name``
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The name of the algorithm, such as 'plain', 'plain64', 'essiv', etc.
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Support of the specific algorithm is hypervisor dependent.
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``hash``
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An optional hash algorithm such as 'md5', 'sha1', 'sha256', etc. Support
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of the specific ivgen hash algorithm is hypervisor dependent.
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``luks2`` format
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~~~~~~~~~~~~~~~~
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The ``luks2`` format is currently supported only by the ``librbd`` engine, and
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can only be applied to RBD network disks (RBD images). Since the ``librbd``
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engine is currently not supported by the libvirt storage driver, you cannot use
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it to control such disks. However, pre-formatted RBD luks2 disks can be loaded
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to a qemu VM using the qemu VM driver. A single
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``<secret type='passphrase'...>`` element is expected.
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Examples
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--------
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Assuming a `luks volume type secret <formatsecret.html#usage-type-volume>`__ is
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already defined, a simple example specifying use of the ``luks`` format for
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either volume creation without a specific cipher being defined or as part of a
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domain volume definition:
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::
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<encryption format='luks'>
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<secret type='passphrase' uuid='f52a81b2-424e-490c-823d-6bd4235bc572'/>
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</encryption>
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Here is an example specifying use of the ``luks`` format for a specific cipher
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algorithm for volume creation. :since:`Since 6.10.0,` the ``target`` format can
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also support ``qcow2`` type with ``luks`` encryption.
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::
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<volume>
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<name>twofish.luks</name>
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<capacity unit='G'>5</capacity>
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<target>
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<path>/var/lib/libvirt/images/demo.luks</path>
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<format type='raw'/>
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<encryption format='luks'>
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<secret type='passphrase' uuid='f52a81b2-424e-490c-823d-6bd4235bc572'/>
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<cipher name='twofish' size='256' mode='cbc' hash='sha256'/>
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<ivgen name='plain64' hash='sha256'/>
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</encryption>
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</target>
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</volume>
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