Re: [Qemu-devel] [PATCH 07/13] block: add manage-encryption command (qmp and blockdev)

[Maxim Levitsky <mlevitsk@redhat.com>]

On Tue, 2019-08-20 at 20:27 +0200, Max Reitz wrote:
> On 14.08.19 22:22, Maxim Levitsky wrote:
> > This adds:
> > 
> > * x-blockdev-update-encryption and x-blockdev-erase-encryption qmp commands
> >   Both commands take the QCryptoKeyManageOptions
> >   the x-blockdev-update-encryption is meant for non destructive addition
> >   of key slots / whatever the encryption driver supports in the future
> > 
> >   x-blockdev-erase-encryption is meant for destructive encryption key erase,
> >   in some cases even without way to recover the data.
> > 
> > 
> > * bdrv_setup_encryption callback in the block driver
> >   This callback does both the above functions with 'action' parameter
> > 
> > * QCryptoKeyManageOptions with set of options that drivers can use for encryption managment
> >   Currently it has all the options that LUKS needs, and later it can be extended
> >   (via union) to support more encryption drivers if needed
> > 
> > * blk_setup_encryption / bdrv_setup_encryption - the usual block layer wrappers.
> >   Note that bdrv_setup_encryption takes BlockDriverState and not BdrvChild,
> >   for the ease of use from the qmp code. It is not expected that this function
> >   will be used by anything but qmp and qemu-img code
> > 
> > 
> > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> > ---
> >  block/block-backend.c          |  9 ++++++++
> >  block/io.c                     | 24 ++++++++++++++++++++
> >  blockdev.c                     | 40 ++++++++++++++++++++++++++++++++++
> >  include/block/block.h          | 12 ++++++++++
> >  include/block/block_int.h      | 11 ++++++++++
> >  include/sysemu/block-backend.h |  7 ++++++
> >  qapi/block-core.json           | 36 ++++++++++++++++++++++++++++++
> >  qapi/crypto.json               | 26 ++++++++++++++++++++++
> >  8 files changed, 165 insertions(+)
> 
> Now I don’t know whether you want to keep this interface at all, because
> the cover letter seemed to imply you’d prefer a QMP amend.  But let it
> be said that a QMP amend is no trivial task.  I think the most difficult
> bit is that the qcow2 implementation currently is inherently an offline
> operation.  It isn’t a good idea to use it on a live image.  (Maybe it
> works, but it’s definitely not what I had in mind when I wrote it.)
> 
> So I’ll still take a quick glance at the interface here.
> 
> [...]
> 
> > diff --git a/qapi/block-core.json b/qapi/block-core.json
> > index 0d43d4f37c..53ed411eed 100644
> > --- a/qapi/block-core.json
> > +++ b/qapi/block-core.json
> > @@ -5327,3 +5327,39 @@
> >    'data' : { 'node-name': 'str',
> >               'iothread': 'StrOrNull',
> >               '*force': 'bool' } }
> > +
> > +
> > +##
> > +# @x-blockdev-update-encryption:
> > +#
> > +# Update the encryption keys for an encrypted block device
> > +#
> > +# @node-name: 	  Name of the blockdev to operate on
> > +# @force:         Disable safety checks (use with care)
> > +# @options:       Driver specific options
> > +#
> > +
> > +# Since: 4.2
> > +##
> > +{ 'command': 'x-blockdev-update-encryption',
> > +  'data': { 'node-name' : 'str',
> > +            '*force' : 'bool',
> > +            'options': 'QCryptoEncryptionSetupOptions' } }
> > +
> > +##
> > +# @x-blockdev-erase-encryption:
> > +#
> > +# Erase the encryption keys for an encrypted block device
> > +#
> > +# @node-name: 	  Name of the blockdev to operate on
> 
> Why the tab?
Because checkpatch.pl doesn't warn about this :-)

> 
> > +# @force:         Disable safety checks (use with care)
> 
> I think being a bit more verbose wouldn’t hurt.
> 
> (Same above.)
True about this - this is another reason this is RFC,

I honestly didn't finish the documentation,
since the sudden change to drop all of this interface.


> 
> > +# @options:       Driver specific options
> > +#
> > +# Returns: @QCryptoKeyManageResult
> > +#
> > +# Since: 4.2
> > +##
> > +{ 'command': 'x-blockdev-erase-encryption',
> > +  'data': { 'node-name' : 'str',
> > +            '*force' : 'bool',
> > +            'options': 'QCryptoEncryptionSetupOptions' } }
> > diff --git a/qapi/crypto.json b/qapi/crypto.json
> > index b2a4cff683..69e8b086db 100644
> > --- a/qapi/crypto.json
> > +++ b/qapi/crypto.json
> > @@ -309,3 +309,29 @@
> >    'base': 'QCryptoBlockInfoBase',
> >    'discriminator': 'format',
> >    'data': { 'luks': 'QCryptoBlockInfoLUKS' } }
> > +
> > +
> > +##
> > +# @QCryptoEncryptionSetupOptions:
> > +#
> > +# Driver specific options for encryption key management.
> 
> The options do seem LUKS-specific, but the name of this structure does not.
This is because to be not luks specific we must use some kind of an union
which means that the user has to specify the driver which I didn't want to do.
Now all of you convinced me ( :-) ) to do this so this will be done when I switch
to the amend interface.

> 
> > +# @key-secret: the ID of a QCryptoSecret object providing the password
> > +#              to add or to erase (optional for erase)
> > +#
> > +# @old-key-secret: the ID of a QCryptoSecret object providing the password
> > +#                  that can currently unlock the image
> > +#
> > +# @slot: Key slot to update/erase
> > +#        (optional, for update will select a free slot,
> > +#        for erase will erase all slots that match the password)
> > +#
> > +# @iter-time: number of milliseconds to spend in
> > +#             PBKDF passphrase processing. Currently defaults to 2000
> > +# Since: 4.2
> > +##
> 
> Does it really make sense to use the same structure for erasing and
> updating?  I think there are ways to represent @key-secret vs. @slot
> being alternatives to each other for erase; @iter-time doesn’t seem to
> make sense for erase; and @slot doesn’t seem to make sense for update.
> Also, I don’t know whether to use @key-secret or @old-key-secret for erase.
> 
> All in all, it seems more sensible to me to have separate structs for
> updating and erasing.

The reason for that was to save on code duplication internally.
Internally (as in block device callback, and generic crypto code callback),
both options are folded in one, with 'action' field to distinguish between them
and that structure.
If I use amend interface, I also would have to have some amend option that
will tell to erase the key. It one of the things I wanted to ask you
with that RFC, how would you solve this in single amend interface.

> 
> Max
> 
> > +{ 'struct': 'QCryptoEncryptionSetupOptions',
> > +  'data': { '*key-secret': 'str',
> > +            '*old-key-secret': 'str',
> > +            '*slot': 'int',
> > +            '*iter-time': 'int' } }
> > 
> 
> 

Best regards,
Thanks for the review,
	Maxim Levitsky