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Re: [PATCH] docs/devel: Add introduction to LUKS volume with detached he
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From: |
Daniel P . Berrangé |
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Subject: |
Re: [PATCH] docs/devel: Add introduction to LUKS volume with detached header |
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Date: |
Fri, 12 Jul 2024 14:39:26 +0100 |
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User-agent: |
Mutt/2.2.12 (2023-09-09) |
On Tue, Feb 20, 2024 at 12:04:42AM +0800, Hyman Huang wrote:
> 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
The new file neeeds adding to an index. We don't have anywhere for crypto
yet, so I'm starting a crypto section thus:
diff --git a/docs/devel/crypto.rst b/docs/devel/crypto.rst
new file mode 100644
index 0000000000..39b1c910e7
--- /dev/null
+++ b/docs/devel/crypto.rst
@@ -0,0 +1,10 @@
+.. _crypto-ref:
+
+====================
+Cryptography in QEMU
+====================
+
+.. toctree::
+ :maxdepth: 2
+
+ luks-detached-header
diff --git a/docs/devel/index-internals.rst b/docs/devel/index-internals.rst
index 5636e9cf1d..4ac7725d72 100644
--- a/docs/devel/index-internals.rst
+++ b/docs/devel/index-internals.rst
@@ -20,3 +20,4 @@ Details about QEMU's various subsystems including how to
add features to them.
vfio-iommufd
writing-monitor-commands
virtio-backends
+ crypto
> @@ -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"}}'
This needs indentation by 2 spaces, and the ">" can be dropped.
The same for all examples that follow.
I'm going to make those changes and queue this patch, since
they're trivial.
With regards,
Daniel
--
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