mirror of https://github.com/ceph/ceph
247 lines
10 KiB
ReStructuredText
247 lines
10 KiB
ReStructuredText
======================
|
|
Image Encryption
|
|
======================
|
|
|
|
.. index:: Ceph Block Device; encryption
|
|
|
|
Starting with the Pacific release, image-level encryption can be handled
|
|
internally by RBD clients. This means you can set a secret key that will be
|
|
used to encrypt a specific RBD image. This page describes the scope of the
|
|
RBD encryption feature.
|
|
|
|
.. note::
|
|
The ``krbd`` kernel module does not support encryption at this time.
|
|
|
|
.. note::
|
|
External tools (e.g. dm-crypt, QEMU) can be used as well to encrypt
|
|
an RBD image, and the feature set and limitation set for that use may be
|
|
different than described here.
|
|
|
|
Encryption Format
|
|
=================
|
|
|
|
By default, RBD images are not encrypted. To encrypt an RBD image, it needs to
|
|
be formatted to one of the supported encryption formats. The format operation
|
|
persists encryption metadata to the image. The encryption metadata usually
|
|
includes information such as the encryption format and version, cipher
|
|
algorithm and mode specification, as well as information used to secure the
|
|
encryption key. The encryption key itself is protected by a user-kept secret
|
|
(usually a passphrase), which is never persisted. The basic encryption format
|
|
operation will require specifying the encryption format and a secret.
|
|
|
|
Some of the encryption metadata may be stored as part of the image data,
|
|
typically an encryption header will be written to the beginning of the raw
|
|
image data. This means that the effective image size of the encrypted image may
|
|
be lower than the raw image size. See the `Supported Formats`_ section for more
|
|
details.
|
|
|
|
.. note::
|
|
Unless explicitly (re-)formatted, clones of an encrypted image are
|
|
inherently encrypted using the same format and secret.
|
|
|
|
.. note::
|
|
Clones of an encrypted image are always encrypted.
|
|
Re-formatting to plaintext is not supported.
|
|
|
|
.. note::
|
|
Any data written to the image prior to its format may become unreadable,
|
|
though it may still occupy storage resources.
|
|
|
|
.. note::
|
|
Images with the `journal feature`_ enabled cannot be formatted and encrypted
|
|
by RBD clients.
|
|
|
|
Encryption Load
|
|
=================
|
|
|
|
Formatting an image is a necessary pre-requisite for enabling encryption.
|
|
However, formatted images will still be treated as raw unencrypted images by
|
|
all of the RBD APIs. In particular, an encrypted RBD image can be opened
|
|
by the same APIs as any other image, and raw unencrypted data can be
|
|
read / written. Such raw IOs may risk the integrity of the encryption format,
|
|
for example by overriding encryption metadata located at the beginning of the
|
|
image.
|
|
|
|
In order to safely perform encrypted IO on the formatted image, an additional
|
|
*encryption load* operation should be applied after opening the image. The
|
|
encryption load operation requires supplying the encryption format and a secret
|
|
for unlocking the encryption key for the image itself and each of its explicitly
|
|
formatted ancestor images. Following a successful encryption load operation,
|
|
all IOs for the opened image will be encrypted / decrypted. For a cloned
|
|
image, this includes IOs for ancestor images as well. The encryption keys will
|
|
be stored in-memory by the RBD client until the image is closed.
|
|
|
|
.. note::
|
|
Once encryption has been loaded, no other encryption load / format
|
|
operations can be applied to the context of the opened image.
|
|
|
|
.. note::
|
|
Once encryption has been loaded, API calls for retrieving the image size
|
|
and the parent overlap using the opened image context will return the
|
|
effective image size and the effective parent overlap respectively.
|
|
|
|
.. note::
|
|
Once encryption has been loaded, API calls for resizing the image will
|
|
interpret the specified target size as effective image size.
|
|
|
|
.. note::
|
|
If a clone of an encrypted image is explicitly formatted, the operation of
|
|
flattening the cloned image ceases to be transparent since the parent data
|
|
must be re-encrypted according to the cloned image format as it is copied
|
|
from the parent snapshot. If encryption is not loaded before the flatten
|
|
operation is issued, any parent data that was previously accessible in the
|
|
cloned image may become unreadable.
|
|
|
|
.. note::
|
|
If a clone of an encrypted image is explicitly formatted, the operation of
|
|
shrinking the cloned image ceases to be transparent since in some cases
|
|
(e.g. if the cloned image has snapshots or if the cloned image is being
|
|
shrunk to a size that is not aligned with the object size) it involves
|
|
copying some data from the parent snapshot, similar to flattening. If
|
|
encryption is not loaded before the shrink operation is issued, any parent
|
|
data that was previously accessible in the cloned image may become
|
|
unreadable.
|
|
|
|
.. note::
|
|
Encryption load can be automatically applied when mounting RBD images as
|
|
block devices via `rbd-nbd`_.
|
|
|
|
Supported Formats
|
|
=================
|
|
|
|
LUKS
|
|
~~~~~~~
|
|
|
|
Both LUKS1 and LUKS2 are supported. The data layout is fully compliant with the
|
|
LUKS specification. Thus, images formatted by RBD can be loaded using external
|
|
LUKS-supporting tools such as dm-crypt or QEMU. Furthermore, existing LUKS
|
|
data, created outside of RBD, can be imported (by copying the raw LUKS data
|
|
into the image) and loaded by RBD encryption.
|
|
|
|
.. note::
|
|
The LUKS formats are supported on Linux-based systems only.
|
|
|
|
.. note::
|
|
Currently, only AES-128 and AES-256 encryption algorithms are supported.
|
|
Additionally, xts-plain64 is currently the only supported encryption mode.
|
|
|
|
To use the LUKS format, start by formatting the image:
|
|
|
|
.. prompt:: bash $
|
|
|
|
rbd encryption format [--cipher-alg {aes-128|aes-256}] {image-spec} {luks1|luks2} {passphrase-file}
|
|
|
|
The encryption format operation generates a LUKS header and writes it to the
|
|
beginning of the image. The header is appended with a single keyslot holding a
|
|
randomly-generated encryption key, and is protected by the passphrase read from
|
|
`passphrase-file`.
|
|
|
|
.. note::
|
|
In older versions, if the content of `passphrase-file` ended with a newline
|
|
character, it was stripped off.
|
|
|
|
By default, AES-256 in xts-plain64 mode (which is the current recommended mode,
|
|
and the usual default for other tools) will be used. The format operation
|
|
allows selecting AES-128 as well. Adding / removing passphrases is currently
|
|
not supported by RBD, but can be applied to the raw RBD data using compatible
|
|
tools such as cryptsetup.
|
|
|
|
The LUKS header size can vary (up to 136MiB in LUKS2), but is usually up to
|
|
16MiB, depending on the version of `libcryptsetup` installed. For optimal
|
|
performance, the encryption format will set the data offset to be aligned with
|
|
the image stripe period size. For example, expect a minimum overhead of 8MiB if
|
|
using an image configured with an 8MiB object size and a minimum overhead of
|
|
12MiB if using an image configured with a 4MiB object size and `stripe count`_
|
|
of 3.
|
|
|
|
In LUKS1, sectors, which are the minimal encryption units, are fixed at 512
|
|
bytes. LUKS2 supports larger sectors, and for better performance we set
|
|
the default sector size to the maximum of 4KiB. Writes which are either smaller
|
|
than a sector, or are not aligned to a sector start, will trigger a guarded
|
|
read-modify-write chain on the client, with a considerable latency penalty.
|
|
A batch of such unaligned writes can lead to IO races which will further
|
|
deteriorate performance. Thus it is advisable to avoid using RBD encryption
|
|
in cases where incoming writes cannot be guaranteed to be sector-aligned.
|
|
|
|
To map a LUKS-formatted image run:
|
|
|
|
.. prompt:: bash #
|
|
|
|
rbd device map -t nbd -o encryption-passphrase-file={passphrase-file} {image-spec}
|
|
|
|
Note that for security reasons, both the encryption format and encryption load
|
|
operations are CPU-intensive, and may take a few seconds to complete. For the
|
|
encryption operations of actual image IO, assuming AES-NI is enabled,
|
|
a relative small microseconds latency should be added, as well as a small
|
|
increase in CPU utilization.
|
|
|
|
Examples
|
|
========
|
|
|
|
Create a LUKS2-formatted image with the effective size of 50GiB:
|
|
|
|
.. prompt:: bash $
|
|
|
|
rbd create --size 50G mypool/myimage
|
|
rbd encryption format mypool/myimage luks2 passphrase.bin
|
|
rbd resize --size 50G --encryption-passphrase-file passphrase.bin mypool/myimage
|
|
|
|
``rbd resize`` command at the end grows the image to compensate for the
|
|
overhead associated with the LUKS2 header.
|
|
|
|
Given a LUKS2-formatted image, create a LUKS2-formatted clone with the
|
|
same effective size:
|
|
|
|
.. prompt:: bash $
|
|
|
|
rbd snap create mypool/myimage@snap
|
|
rbd snap protect mypool/myimage@snap
|
|
rbd clone mypool/myimage@snap mypool/myclone
|
|
rbd encryption format mypool/myclone luks2 clone-passphrase.bin
|
|
|
|
Given a LUKS2-formatted image with the effective size of 50GiB, create
|
|
a LUKS1-formatted clone with the same effective size:
|
|
|
|
.. prompt:: bash $
|
|
|
|
rbd snap create mypool/myimage@snap
|
|
rbd snap protect mypool/myimage@snap
|
|
rbd clone mypool/myimage@snap mypool/myclone
|
|
rbd encryption format mypool/myclone luks1 clone-passphrase.bin
|
|
rbd resize --size 50G --allow-shrink --encryption-passphrase-file clone-passphrase.bin --encryption-passphrase-file passphrase.bin mypool/myclone
|
|
|
|
Since LUKS1 header is usually smaller than LUKS2 header, ``rbd resize``
|
|
command at the end shrinks the cloned image to get rid of unneeded
|
|
space allowance.
|
|
|
|
Given a LUKS1-formatted image with the effective size of 50GiB, create
|
|
a LUKS2-formatted clone with the same effective size:
|
|
|
|
.. prompt:: bash $
|
|
|
|
rbd resize --size 51G mypool/myimage
|
|
rbd snap create mypool/myimage@snap
|
|
rbd snap protect mypool/myimage@snap
|
|
rbd clone mypool/myimage@snap mypool/myclone
|
|
rbd encryption format mypool/myclone luks2 clone-passphrase.bin
|
|
rbd resize --size 50G --allow-shrink --encryption-passphrase-file passphrase.bin mypool/myimage
|
|
rbd resize --size 50G --allow-shrink --encryption-passphrase-file clone-passphrase.bin --encryption-passphrase-file passphrase.bin mypool/myclone
|
|
|
|
Since LUKS2 header is usually bigger than LUKS1 header, ``rbd resize``
|
|
command at the beginning temporarily grows the parent image to reserve
|
|
some extra space in the parent snapshot and consequently the cloned
|
|
image. This is necessary to make all parent data accessible in the
|
|
cloned image. ``rbd resize`` commands at the end shrink the parent
|
|
image back to its original size (this does not impact the parent
|
|
snapshot) and also the cloned image to get rid of unused reserved
|
|
space.
|
|
|
|
The same applies to creating a formatted clone of an unformatted
|
|
(plaintext) image since an unformatted image does not have a header at
|
|
all.
|
|
|
|
.. _journal feature: ../rbd-mirroring/#enable-image-journaling-feature
|
|
.. _Supported Formats: #supported-formats
|
|
.. _rbd-nbd: ../../man/8/rbd-nbd
|
|
.. _stripe count: ../../man/8/rbd/#striping
|