Looks like this fell through the cracks. Is anyone familiar with LUKS willing to review it?
Hyman Huang <yong.hu...@smartx.com> writes: > Signed-off-by: Hyman Huang <yong.hu...@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.hu...@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.lur...@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.