Re: [Qemu-devel] [PATCH v2 06/17] crypto: add block encryption framework

[Daniel P. Berrange]

On Thu, Feb 04, 2016 at 05:23:32PM -0700, Eric Blake wrote:
> On 01/20/2016 10:38 AM, Daniel P. Berrange wrote:
> > Add a generic framework for support different block encryption
> > formats. Upon instantiating a QCryptoBlock object, it will read
> > the encryption header and extract the encryption keys. It is
> > then possible to call methods to encrypt/decrypt data buffers.
> > 
> > There is also a mode whereby it will create/initialize a new
> > encryption header on a previously unformatted volume.
> > 
> > The initial framework comes with support for the legacy QCow
> > AES based encryption. This enables code in the QCow driver to
> > be consolidated later.
> > 
> > Signed-off-by: Daniel P. Berrange <address@hidden>
> > ---
> >  crypto/Makefile.objs      |   2 +
> >  crypto/block-qcow.c       | 167 +++++++++++++++++++++++++++++
> >  crypto/block-qcow.h       |  28 +++++
> >  crypto/block.c            | 263 
> > ++++++++++++++++++++++++++++++++++++++++++++++
> >  crypto/blockpriv.h        |  90 ++++++++++++++++
> >  include/crypto/block.h    | 233 ++++++++++++++++++++++++++++++++++++++++
> >  qapi/crypto.json          |  67 ++++++++++++
> >  tests/.gitignore          |   1 +
> >  tests/Makefile            |   2 +
> >  tests/test-crypto-block.c | 239 +++++++++++++++++++++++++++++++++++++++++
> >  10 files changed, 1092 insertions(+)
> >  create mode 100644 crypto/block-qcow.c
> >  create mode 100644 crypto/block-qcow.h
> >  create mode 100644 crypto/block.c
> >  create mode 100644 crypto/blockpriv.h
> >  create mode 100644 include/crypto/block.h
> >  create mode 100644 tests/test-crypto-block.c
> > 
> 
> > +++ b/crypto/block-qcow.c
> > @@ -0,0 +1,167 @@
> > +/*
> > + * QEMU Crypto block device encryption QCow/QCow2 AES-CBC format
> > + *
> > + * Copyright (c) 2015-2016 Red Hat, Inc.
> > + *
> > + * This library is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU Lesser General Public
> > + * License as published by the Free Software Foundation; either
> > + * version 2 of the License, or (at your option) any later version.
> > + *
> > + * This library is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > + * Lesser General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU Lesser General Public
> > + * License along with this library; if not, see 
> > <http://www.gnu.org/licenses/>.
> > + *
> > + */
> 
> Maybe worth a big comment stating that this file exists for backwards
> compatibility, and no one in their right mind should copy the code
> and/or encrypt new files with it.

Heh, yeah.

> > +static gboolean
> > +qcrypto_block_qcow_has_format(const uint8_t *buf G_GNUC_UNUSED,
> > +                              size_t buf_size G_GNUC_UNUSED)
> > +{
> > +    return false;
> > +}
> 
> When I see gboolean, I think TRUE/FALSE.  Yes, C99 'false' happens to
> promote to the correct value for whatever integer type gboolean is, but
> this would read nicer if it returned 'bool'.

Yeah, dunno what I was thinking really. I use gboolean in a few places
due to the gmainloop callback API contract, but this should not have
needed it.

> > +static int
> > +qcrypto_block_qcow_init(QCryptoBlock *block,
> > +                        const char *keysecret,
> > +                        Error **errp)
> > +{
> > +    char *password;
> > +    int ret;
> > +    uint8_t keybuf[16];
> > +    int len, i;
> > +
> > +    memset(keybuf, 0, 16);
> > +
> > +    password = qcrypto_secret_lookup_as_utf8(keysecret, errp);
> > +    if (!password) {
> > +        return -1;
> > +    }
> > +
> > +    len = strlen(password);
> > +    if (len > 16) {
> > +        len = 16;
> > +    }
> > +    for (i = 0; i < len; i++) {
> > +        keybuf[i] = password[i];
> > +    }
> 
> What - we really throw away anything longer than 16 bytes?

Yes, that's how awesome legacy qcow2 encryption is :-)

> Would a memcpy() be any nicer than an open-coded loop?

Sure.

> > +++ b/crypto/blockpriv.h
> 
> > +
> > +typedef struct QCryptoBlockDriver QCryptoBlockDriver;
> > +
> > +struct QCryptoBlock {
> > +    QCryptoBlockFormat format;
> > +
> > +    const QCryptoBlockDriver *driver;
> > +    void *opaque;
> > +
> > +    QCryptoCipher *cipher;
> > +    QCryptoIVGen *ivgen;
> > +    QCryptoHashAlgorithm kdfhash;
> > +    size_t niv;
> > +    uint64_t payload_offset; /* In 512 byte sectors */
> 
> Someday, we may want to support 4k sectors natively.  I don't envy the
> person making the conversion, but we could at least make their life
> easier by representing this in bytes instead of units of 512-byte sectors.

Ok will do.

> > +};
> > +
> > +struct QCryptoBlockDriver {
> > +    int (*open)(QCryptoBlock *block,
> > +                QCryptoBlockOpenOptions *options,
> > +                QCryptoBlockReadFunc readfunc,
> > +                void *opaque,
> > +                unsigned int flags,
> > +                Error **errp);
> 
> No documentation on any of these contracts?

They're essentially identical to the public API contracts, so I
figured it was redundant to duplicate those docs.


> > +/**
> > + * qcrypto_block_has_format:
> > + * @format: the encryption format
> > + * @buf: the data from head of the volume
> > + * @len: the length of @buf in bytes
> > + *
> > + * Given @len bytes of data from the head of a storage volume
> > + * in @buf, probe to determine if the volume has the encryption
> > + * format specified in @format.
> > + *
> > + * Returns: true if the data in @buf matches @format
> > + */
> > +gboolean qcrypto_block_has_format(QCryptoBlockFormat format,
> 
> Again, this should probably be 'bool', not gboolean.

Yep


> > +QCryptoBlock *qcrypto_block_create(QCryptoBlockCreateOptions *options,
> > +                                   QCryptoBlockInitFunc initfunc,
> > +                                   QCryptoBlockWriteFunc writefunc,
> > +                                   void *opaque,
> > +                                   Error **errp);
> > +
> > +/**
> > + * @qcrypto_block_decrypt:
> > + * @block: the block encryption object
> > + * @startsector: the sector from which @buf was read
> 
> From the guest's point of view, right?

Yes & no, it is the sector of whatever underlying storage holds
the image. If there are other formats beneath the crypto format
it might not correspond to the guest OS seen sector.


> > +/**
> > + * qcrypto_block_get_payload_offset:
> > + * @block: the block encryption object
> > + *
> > + * Get the offset to the payload indicated by the
> > + * encryption header. The offset is measured in
> > + * 512 byte sectors
> > + *
> > + * Returns: the payload offset in sectors.
> > + */
> > +uint64_t qcrypto_block_get_payload_offset(QCryptoBlock *block);
> 
> Please, let's use bytes here, not sectors.

Ok


Regards,
Daniel
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