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