Re: [PATCH] docs/devel: Add introduction to LUKS volume with detached header

[Markus Armbruster <armbru@redhat.com>]

Looks like this fell through the cracks.  Is anyone familiar with LUKS
willing to review it?

Hyman Huang <yong.huang@smartx.com> writes:

> Signed-off-by: Hyman Huang <yong.huang@smartx.com>
> ---
>  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 <yong.huang@smartx.com>
>  S: Maintained
>  F: tests/qemu-iotests/tests/luks-detached-header
> +F: docs/devel/luks-detached-header.rst
>  
>  D-Bus
>  M: Marc-André Lureau <marcandre.lureau@redhat.com>
> 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.