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Mon, 19 Feb 2024 08:04:48 -0800 (PST) From: Hyman Huang To: qemu-devel@nongnu.org Cc: =?utf-8?q?Daniel_P_=2E_Berrang=C3=A9?= , Markus Armbruster , Kevin Wolf , Hanna Reitz , Eric Blake , yong.huang@smartx.com Subject: [PATCH] docs/devel: Add introduction to LUKS volume with detached header Date: Tue, 20 Feb 2024 00:04:42 +0800 Message-Id: X-Mailer: git-send-email 2.39.3 MIME-Version: 1.0 Received-SPF: none client-ip=2607:f8b0:4864:20::c29; envelope-from=yong.huang@smartx.com; helo=mail-oo1-xc29.google.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_NONE=0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Signed-off-by: Hyman Huang --- MAINTAINERS | 1 + docs/devel/luks-detached-header.rst | 182 ++++++++++++++++++++++++++++ 2 files changed, 183 insertions(+) create mode 100644 docs/devel/luks-detached-header.rst diff --git a/MAINTAINERS b/MAINTAINERS index a24c2b51b6..e8b03032ab 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -3422,6 +3422,7 @@ Detached LUKS header M: Hyman Huang S: Maintained F: tests/qemu-iotests/tests/luks-detached-header +F: docs/devel/luks-detached-header.rst D-Bus M: Marc-André Lureau diff --git a/docs/devel/luks-detached-header.rst b/docs/devel/luks-detached-header.rst new file mode 100644 index 0000000000..15e9ccde1d --- /dev/null +++ b/docs/devel/luks-detached-header.rst @@ -0,0 +1,182 @@ +================================ +LUKS volume with detached header +================================ + +Introduction +============ + +This document gives an overview of the design of LUKS volume with detached +header and how to use it. + +Background +========== + +The LUKS format has ability to store the header in a separate volume from +the payload. We could extend the LUKS driver in QEMU to support this use +case. + +Normally a LUKS volume has a layout: + +:: + + +-----------------------------------------------+ + | | | | + disk | header | key material | disk payload data | + | | | | + +-----------------------------------------------+ + +With a detached LUKS header, you need 2 disks so getting: + +:: + + +--------------------------+ + disk1 | header | key material | + +--------------------------+ + +---------------------+ + disk2 | disk payload data | + +---------------------+ + +There are a variety of benefits to doing this: + + * Secrecy - the disk2 cannot be identified as containing LUKS + volume since there's no header + * Control - if access to the disk1 is restricted, then even + if someone has access to disk2 they can't unlock + it. Might be useful if you have disks on NFS but + want to restrict which host can launch a VM + instance from it, by dynamically providing access + to the header to a designated host + * Flexibility - your application data volume may be a given + size and it is inconvenient to resize it to + add encryption.You can store the LUKS header + separately and use the existing storage + volume for payload + * Recovery - corruption of a bit in the header may make the + entire payload inaccessible. It might be + convenient to take backups of the header. If + your primary disk header becomes corrupt, you + can unlock the data still by pointing to the + backup detached header + +Architecture +============ + +Take the qcow2 encryption, for example. The architecture of the +LUKS volume with detached header is shown in the diagram below. + +There are two children of the root node: a file and a header. +Data from the disk payload is stored in the file node. The +LUKS header and key material are located in the header node, +as previously mentioned. + +:: + + +-----------------------------+ + Root node | foo[luks] | + +-----------------------------+ + | | + file | header | + | | + +---------------------+ +------------------+ + Child node |payload-format[qcow2]| |header-format[raw]| + +---------------------+ +------------------+ + | | + file | file | + | | + +----------------------+ +---------------------+ + Child node |payload-protocol[file]| |header-protocol[file]| + +----------------------+ +---------------------+ + | | + | | + | | + Host storage Host storage + +Usage +===== + +Create a LUKS disk with a detached header using qemu-img +-------------------------------------------------------- + +Shell commandline:: + +# qemu-img create --object secret,id=sec0,data=abc123 -f luks \ +> -o cipher-alg=aes-256,cipher-mode=xts -o key-secret=sec0 \ +> -o detached-header=true test-header.img +# qemu-img create -f qcow2 test-payload.qcow2 200G +# qemu-img info 'json:{"driver":"luks","file":{"filename": \ +> "test-payload.img"},"header":{"filename":"test-header.img"}}' + +Set up a VM's LUKS volume with a detached header +------------------------------------------------ + +Qemu commandline:: + +# qemu-system-x86_64 ... \ +> -object '{"qom-type":"secret","id":"libvirt-3-format-secret", \ +> "data":"abc123"}' \ +> -blockdev '{"driver":"file","filename":"/path/to/test-header.img", \ +> "node-name":"libvirt-1-storage"}' \ +> -blockdev '{"node-name":"libvirt-1-format","read-only":false, \ +> "driver":"raw","file":"libvirt-1-storage"}' \ +> -blockdev '{"driver":"file","filename":"/path/to/test-payload.qcow2", \ +> "node-name":"libvirt-2-storage"}' \ +> -blockdev '{"node-name":"libvirt-2-format","read-only":false, \ +> "driver":"qcow2","file":"libvirt-2-storage"}' \ +> -blockdev '{"node-name":"libvirt-3-format","driver":"luks", \ +> "file":"libvirt-2-format","header":"libvirt-1-format","key-secret": \ +> "libvirt-3-format-secret"}' \ +> -device '{"driver":"virtio-blk-pci","bus":XXX,"addr":YYY,"drive": \ +> "libvirt-3-format","id":"virtio-disk1"}' + +Add LUKS volume to a VM with a detached header +---------------------------------------------- + +1. object-add the secret for decrypting the cipher stored in + LUKS header above:: + +# virsh qemu-monitor-command vm '{"execute":"object-add", \ +> "arguments":{"qom-type":"secret", "id": \ +> "libvirt-4-format-secret", "data":"abc123"}}' + +2. block-add the protocol node for LUKS header:: + +# virsh qemu-monitor-command vm '{"execute":"blockdev-add", \ +> "arguments":{"node-name":"libvirt-1-storage", "driver":"file", \ +> "filename": "/path/to/test-header.img" }}' + +3. block-add the raw-drived node for LUKS header:: + +# virsh qemu-monitor-command vm '{"execute":"blockdev-add", \ +> "arguments":{"node-name":"libvirt-1-format", "driver":"raw", \ +> "file":"libvirt-1-storage"}}' + +4. block-add the protocol node for disk payload image:: + +# virsh qemu-monitor-command vm '{"execute":"blockdev-add", \ +> "arguments":{"node-name":"libvirt-2-storage", "driver":"file", \ +> "filename":"/path/to/test-payload.qcow2"}}' + +5. block-add the qcow2-drived format node for disk payload data:: + +# virsh qemu-monitor-command vm '{"execute":"blockdev-add", \ +> "arguments":{"node-name":"libvirt-2-format", "driver":"qcow2", \ +> "file":"libvirt-2-storage"}}' + +6. block-add the luks-drived format node to link the qcow2 disk + with the LUKS header by specifying the field "header":: + +# virsh qemu-monitor-command vm '{"execute":"blockdev-add", \ +> "arguments":{"node-name":"libvirt-3-format", "driver":"luks", \ +> "file":"libvirt-2-format", "header":"libvirt-1-format", \ +> "key-secret":"libvirt-2-format-secret"}}' + +7. hot-plug the virtio-blk device finally:: + +# virsh qemu-monitor-command vm '{"execute":"device_add", \ +> "arguments": {"driver":"virtio-blk-pci", \ +> "drive": "libvirt-3-format", "id":"virtio-disk2"}} + +TODO +==== + +1. Support the shared detached LUKS header within the VM.