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[Qemu-devel] [PATCH v2 00/17] Convert QCow[2] to QCryptoBlock & add LUKS

From: Daniel P. Berrange
Subject: [Qemu-devel] [PATCH v2 00/17] Convert QCow[2] to QCryptoBlock & add LUKS support
Date: Tue, 24 Jan 2017 14:51:35 +0000

This series is a continuation of previous work to support LUKS in
QEMU. The existing merged code supports LUKS as a standalone
driver which can be layered over/under any other QEMU block device
driver. This works well when using LUKS over protocol drivers (file,
rbd, iscsi, etc, etc), but has some downsides when combined with
format drivers like qcow2.

If you layer LUKS under qcow2 (eg qcow2 -> luks -> file) then you
cannot get any information about the qcow2 file without first
decrypting it, as both the header and payload are encrypted.

If you layer LUKS over qcow2 (eg luks -> qcow2 -> file) then you
cannot distinguish between a qcow2 file where the guest has done
LUKS encryption from a qcow2 file which qemu has done encryption.
More seriously, when encrypting sectors the guest virtual sector
is used as the input for deriving the initialization vectors.
When internal snapshots are used, this means that multiple sectors
in the qcow2 file may be encrypted with the same initialization
vector. This is a security weakness when combined with certain
cryptographic modes.

Integrating LUKS natively into qcow2 allows us to combine the
best aspects of both layering strategies above. In particular
the header remains unecrypted, but initialization vectors are
generated using physical sector numbers preserving security
when snapshots are used. This is a change from previous postings
of this work, where the IVs were (incorrectly) generated based
on the virtual disk sector.

In a previous posting of this work, Fam had suggested that we
do integration by layering luks over qcow2, but having QEMU
block layer automatically create the luks driver above qcow2
based on the qcow2 header crypt_method field. This is not
possible though, because such a scheme would suffer from the
problem of IVs being generated from the virtual disk sector
instead of physical disk sector. So having LUKS specific
code in the qcow2 block driver is unavoidable. In comparison
to the previous posting though, the amount of code in qcow2.c
has been reduced by allowing re-use of code from block/crypto.c
for handling QemuOpts -> QAPI conversion. So extra lines of
code in qcow2 to support LUKS is < 200.

I have also split the changes to qcow2 up into 2 patches. The
first patch simply introduces use of the QCryptoBlock framework
to qcow2 for the existing (deprecated) AES-CBC encryption method.
The second patch wires up the LUKS support for qcow2. This makes
it clearer which parts of the changes are related to plain code
refactoring, vs enabling the new features. Specifically we can
now see that the LUKS enablement in qcow2 has this footprint:

Changed in v2:

 - Split qcow2 LUKS tests into separate patch
 - Split qcow2 LUKS spec addition into separate patch
 - Use strstart instead of g_str_has_prefix + pointer manipulation
 - Use -1 instead of 1 for error condition when iterating over opts
 - Fix formatting of qemu-img manpage for qcow2 AES flaws list
 - Fix writing zeros in qcow when encrypting sector
 - Don't overwrite input data buffer in qcow2 when encrypting data
 - Use TODO instead of XXX markers
 - Rename qcow2_change_encryption to qcow2_set_up_encryption
 - Add missing QEMU_IO_OPTIONS_NO_FMT variable to iotests
 - Explicitly fill crypto header unused space with zeros
 - Fix byte-swapping of crypto header in qcow2
 - Enforce crypto header offset is multiple of cluster size
 - Move setting of crypt_physical_offset flag
 - Fix docs for 'encryption-format' option
 - Deprecate legacy 'encryption' option
 - Drop redundant test scenarios
 - Use small file sizes for iotests
 - Drop pbkdf iteration time to 10ms during iotests
 - Use separate passphrase for top vs backing file in iotests
 - Mark 'encryption_key_missing@ field as deprecated

Daniel P. Berrange (17):
  block: expose crypto option names / defs to other drivers
  block: add ability to set a prefix for opt names
  qcow: document another weakness of qcow AES encryption
  qcow: require image size to be > 1 for new images
  iotests: skip 042 with qcow which dosn't support zero sized images
  iotests: skip 048 with qcow which doesn't support resize
  iotests: fix 097 when run with qcow
  qcow: make encrypt_sectors encrypt in place
  qcow: convert QCow to use QCryptoBlock for encryption
  qcow2: make qcow2_encrypt_sectors encrypt in place
  qcow2: convert QCow2 to use QCryptoBlock for encryption
  qcow2: extend specification to cover LUKS encryption
  qcow2: add support for LUKS encryption format
  qcow2: add iotests to cover LUKS encryption support
  iotests: enable tests 134 and 158 to work with qcow (v1)
  block: rip out all traces of password prompting
  block: remove all encryption handling APIs

 block.c                    |  77 +--------
 block/crypto.c             | 167 +++++++++++-------
 block/crypto.h             | 102 +++++++++++
 block/qapi.c               |   2 +-
 block/qcow.c               | 215 ++++++++++-------------
 block/qcow2-cluster.c      |  56 +-----
 block/qcow2-refcount.c     |  10 ++
 block/qcow2.c              | 414 ++++++++++++++++++++++++++++++++++++---------
 block/qcow2.h              |  18 +-
 blockdev.c                 |  37 +---
 docs/specs/qcow2.txt       |  96 +++++++++++
 hmp.c                      |  31 ----
 include/block/block.h      |   3 -
 include/block/block_int.h  |   1 -
 include/monitor/monitor.h  |   7 -
 include/qapi/error.h       |   1 -
 include/qemu/osdep.h       |   2 -
 monitor.c                  |  68 --------
 qapi-schema.json           |  10 +-
 qapi/block-core.json       |  35 +++-
 qapi/common.json           |   5 +-
 qemu-img.c                 |  31 ----
 qemu-img.texi              |  19 ++-
 qemu-io.c                  |  20 ---
 qmp.c                      |  12 +-
 tests/qemu-iotests/042     |   2 +-
 tests/qemu-iotests/048     |   2 +-
 tests/qemu-iotests/049     |   2 +-
 tests/qemu-iotests/049.out |   4 +-
 tests/qemu-iotests/082.out | 297 +++++++++++++++++++++++++++++---
 tests/qemu-iotests/087     |  37 +++-
 tests/qemu-iotests/087.out |  16 +-
 tests/qemu-iotests/097     |  10 +-
 tests/qemu-iotests/097.out | 125 +-------------
 tests/qemu-iotests/134     |  20 ++-
 tests/qemu-iotests/134.out |  10 +-
 tests/qemu-iotests/158     |  21 ++-
 tests/qemu-iotests/158.out |  14 +-
 tests/qemu-iotests/173     | 126 ++++++++++++++
 tests/qemu-iotests/173.out | 119 +++++++++++++
 tests/qemu-iotests/174     |  76 +++++++++
 tests/qemu-iotests/174.out |  19 +++
 tests/qemu-iotests/175     |  86 ++++++++++
 tests/qemu-iotests/175.out |  26 +++
 tests/qemu-iotests/common  |  10 +-
 tests/qemu-iotests/group   |   3 +
 util/oslib-posix.c         |  66 --------
 util/oslib-win32.c         |  24 ---
 48 files changed, 1628 insertions(+), 926 deletions(-)
 create mode 100644 block/crypto.h
 create mode 100755 tests/qemu-iotests/173
 create mode 100644 tests/qemu-iotests/173.out
 create mode 100755 tests/qemu-iotests/174
 create mode 100644 tests/qemu-iotests/174.out
 create mode 100755 tests/qemu-iotests/175
 create mode 100644 tests/qemu-iotests/175.out


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