Re: [Qemu-devel] [PATCH v9 13/20] qcow2: add support for LUKS encryption format

[Max Reitz <mreitz@redhat.com>]

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On 2017-06-21 16:42, Max Reitz wrote:
> On 2017-06-19 19:34, Daniel P. Berrange wrote:
>> This adds support for using LUKS as an encryption format
>> with the qcow2 file, using the new encrypt.format parameter
>> to request "luks" format. e.g.
>>
>>   # qemu-img create --object secret,data=123456,id=sec0 \
>>        -f qcow2 -o encrypt.format=luks,encrypt.key-secret=sec0 \
>>        test.qcow2 10G
>>
>> 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,encrypt.key-secret=sec0 \
>>        test.qcow2 10G
>>
>>  # qemu-img create --object secret,data=123456,id=sec0 \
>>        -f qcow2 -o encryption-format=aes,encrypt.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.
>>
>> Reviewed-by: Eric Blake <eblake@redhat.com>
>> Reviewed-by: Alberto Garcia <berto@igalia.com>
>> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
>> ---
>>  block/qcow2-cluster.c      |   4 +-
>>  block/qcow2-refcount.c     |  10 ++
>>  block/qcow2.c              | 268 ++++++++++++++++++++++++++++++++++++++------
>>  block/qcow2.h              |   9 ++
>>  qapi/block-core.json       |   5 +-
>>  tests/qemu-iotests/082.out | 270 ++++++++++++++++++++++++++++++++++++---------
>>  6 files changed, 478 insertions(+), 88 deletions(-)
> 
> Reviewed-by: Max Reitz <mreitz@redhat.com>

(But due to the split of do_perform_cow(), this will need the same
changes that patch 10 and 11 will need (in this case only contextual, in
the cases of 10 and 11 there are also functional changes required).)


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