Re: [Qemu-devel] [PATCH v3 13/18] qcow2: add support for LUKS encryption format

[Max Reitz <mreitz@redhat.com>]

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On 26.01.2017 11:18, Daniel P. Berrange wrote:
> This adds support for using LUKS as an encryption format
> with the qcow2 file. The use of the existing 'encryption=on'
> parameter is replaced by a new parameter 'encryption-format'
> which takes the values 'aes' or 'luks'. e.g.
> 
>   # qemu-img create --object secret,data=123456,id=sec0 \
>        -f qcow2 -o encryption-format=luks,luks-key-secret=sec0 \
>        test.qcow2 10G
> 
> results in the creation of an image using the LUKS format.
> Use of the legacy 'encryption=on' parameter still results
> in creation of the old qcow2 AES format, and is equivalent
> to the new 'encryption-format=aes'. e.g. the following are
> equivalent:
> 
>   # qemu-img create --object secret,data=123456,id=sec0 \
>        -f qcow2 -o encryption=on,aes-key-secret=sec0 \
>        test.qcow2 10G
> 
>  # qemu-img create --object secret,data=123456,id=sec0 \
>        -f qcow2 -o encryption-format=aes,aes-key-secret=sec0 \
>        test.qcow2 10G
> 
> With the LUKS format it is necessary to store the LUKS
> partition header and key material in the QCow2 file. This
> data can be many MB in size, so cannot go into the QCow2
> header region directly. Thus the spec defines a FDE
> (Full Disk Encryption) header extension that specifies
> the offset of a set of clusters to hold the FDE headers,
> as well as the length of that region. The LUKS header is
> thus stored in these extra allocated clusters before the
> main image payload.
> 
> Aside from all the cryptographic differences implied by
> use of the LUKS format, there is one further key difference
> between the use of legacy AES and LUKS encryption in qcow2.
> For LUKS, the initialiazation vectors are generated using
> the host physical sector as the input, rather than the
> guest virtual sector. This guarantees unique initialization
> vectors for all sectors when qcow2 internal snapshots are
> used, thus giving stronger protection against watermarking
> attacks.
> 
> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> ---
>  block/qcow2-cluster.c      |   4 +-
>  block/qcow2-refcount.c     |  10 ++
>  block/qcow2.c              | 284 +++++++++++++++++++++++++++++++++++++++------
>  block/qcow2.h              |   9 ++
>  include/block/block_int.h  |   1 +
>  qapi/block-core.json       |  11 +-
>  qemu-img.c                 |   4 +-
>  tests/qemu-iotests/082.out | 270 +++++++++++++++++++++++++++++++++++++-----
>  8 files changed, 527 insertions(+), 66 deletions(-)
> 

[...]

> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 4943942..d15c6a9 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -2327,9 +2327,15 @@
>  #                         caches. The interval is in seconds. The default value
>  #                         is 0 and it disables this feature (since 2.5)
>  # @aes-key-secret:        #optional the ID of a QCryptoSecret object providing
> -#                         the AES decryption key (since 2.9). Mandatory for
> +#                         the AES decryption key (since 2.9). Mandatory for AES
>  #                         encrypted images, except when doing a metadata-only
>  #                         probe of the image.
> +#                         the AES decryption key (since 2.9) Mandatory except
> +#                         when doing a metadata-only probe of the image.

I think these two lines should be omitted (rebase artifact?).

With that fixed:

Reviewed-by: Max Reitz <mreitz@redhat.com>

> +# @luks-key-secret:       #optional the ID of a QCryptoSecret object providing
> +#                         the LUKS keyslot passphrase (since 2.9). Mandatory for
> +#                         LUKS encrypted images, except when doing a metadata-
> +#                         only probe of the image.
>  #
>  # Since: 1.7
>  ##

[...]


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