Re: [PATCH RESEND v3 02/10] crypto: Support generic LUKS encryption

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, Dec 25, 2023 at 01:45:04PM +0800, Hyman Huang wrote:
> By enhancing the LUKS driver, it is possible to enable
> the detachable LUKS header and, as a result, achieve
> general encryption for any disk format that QEMU has
> supported.
> 
> Take the qcow2 as an example, the usage of the generic
> LUKS encryption as follows:
> 
> 1. add a protocol blockdev node of data disk
> $ virsh qemu-monitor-command vm '{"execute":"blockdev-add",
> > "arguments":{"node-name":"libvirt-1-storage", "driver":"file",
> > "filename":"/path/to/test_disk.qcow2"}}'
> 
> 2. add a protocol blockdev node of LUKS header as above.
> $ virsh qemu-monitor-command vm '{"execute":"blockdev-add",
> > "arguments":{"node-name":"libvirt-2-storage", "driver":"file",
> > "filename": "/path/to/cipher.gluks" }}'
> 
> 3. add the secret for decrypting the cipher stored in LUKS
>    header above
> $ virsh qemu-monitor-command vm '{"execute":"object-add",
> > "arguments":{"qom-type":"secret", "id":
> > "libvirt-2-storage-secret0", "data":"abc123"}}'
> 
> 4. add the qcow2-drived blockdev format node
> $ virsh qemu-monitor-command vm '{"execute":"blockdev-add",
> > "arguments":{"node-name":"libvirt-1-format", "driver":"qcow2",
> > "file":"libvirt-1-storage"}}'
> 
> 5. add the luks-drived blockdev to link the qcow2 disk with
>    LUKS header by specifying the field "header"
> $ virsh qemu-monitor-command vm '{"execute":"blockdev-add",
> > "arguments":{"node-name":"libvirt-2-format", "driver":"luks",
> > "file":"libvirt-1-format", "header":"libvirt-2-storage",
> > "key-secret":"libvirt-2-format-secret0"}}'
> 
> 6. add the virtio-blk device finally
> $ virsh qemu-monitor-command vm '{"execute":"device_add",
> > "arguments": {"num-queues":"1", "driver":"virtio-blk-pci",
> > "drive": "libvirt-2-format", "id":"virtio-disk2"}}'
> 
> The generic LUKS encryption method of starting a virtual
> machine (VM) is somewhat similar to hot-plug in that both
> maintaining the same json command while the starting VM
> changes the "blockdev-add/device_add" parameters to
> "blockdev/device".
> 
> Signed-off-by: Hyman Huang <yong.huang@smartx.com>
> Message-Id: <910801f303da1601051479d3b7e5c2c6b4e01eb7.1701879996.git.yong.huang@smartx.com>
> ---
>  block/crypto.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/block/crypto.c b/block/crypto.c
> index f82b13d32b..6063879bac 100644
> --- a/block/crypto.c
> +++ b/block/crypto.c
> @@ -64,12 +64,14 @@ static int block_crypto_read_func(QCryptoBlock *block,
>                                    Error **errp)
>  {
>      BlockDriverState *bs = opaque;
> +    BlockCrypto *crypto = bs->opaque;
>      ssize_t ret;
>  
>      GLOBAL_STATE_CODE();
>      GRAPH_RDLOCK_GUARD_MAINLOOP();
>  
> -    ret = bdrv_pread(bs->file, offset, buflen, buf, 0);
> +    ret = bdrv_pread(crypto->header ? crypto->header : bs->file,
> +                     offset, buflen, buf, 0);
>      if (ret < 0) {
>          error_setg_errno(errp, -ret, "Could not read encryption header");
>          return ret;
> @@ -269,6 +271,7 @@ static int block_crypto_open_generic(QCryptoBlockFormat format,
>      QCryptoBlockOpenOptions *open_opts = NULL;
>      unsigned int cflags = 0;
>      QDict *cryptoopts = NULL;
> +    const char *hdr_bdref = qdict_get_try_str(options, "header");

This is an invalid check to make, because it is assuming the user is
referencing a separate blockdev node name and doesn't work for an
inline definition. eg

  qemu-img info  'json:{"driver":"luks","file":{"filename":"test-payload.img"},"header":{"filename":"test-header.img"}}'


>  
>      GLOBAL_STATE_CODE();
>  
> @@ -277,6 +280,15 @@ static int block_crypto_open_generic(QCryptoBlockFormat format,
>          return ret;
>      }
>  
> +    if (hdr_bdref) {

Get rid of this 'if' clause and unconditionally call the next line:

> +        crypto->header = bdrv_open_child(NULL, options, "header", bs,
> +                                         &child_of_bds, BDRV_CHILD_METADATA,
> +                                         false, errp);

but pass 'true' instead of 'false' here to allow the child to be absent,
and thus let it return NULL.

> +        if (!crypto->header) {

You'll need to then check  '*errp != NULL' instead

You'll also need "ERRP_GUARD" at the start of the method

> +            return -EINVAL;
> +        }
> +    }
> +
>      GRAPH_RDLOCK_GUARD_MAINLOOP();
>  
>      bs->supported_write_flags = BDRV_REQ_FUA &

This patch should be combined with the previous patch that adds the new
QAPI schema element as splitting them doesn't add value.


Testing this patch with the changes I suggest above, however, still does
not work:

  $ dd if=/dev/zero of=test-header.img bs=1M count=32
  $ dd if=/dev/zero of=test-payload.img bs=1M count=1000
  $ cryptsetup luksFormat  --header test-header.img test-payload.img  --force-password --type luks1
  $ qemu-img info  'json:{"driver":"luks","file":{"filename":"test-payload.img"},"header":{"filename":"test-header.img"}}'
  qemu-img: Could not open 'json:{"driver":"luks","file":{"filename":"test-payload.img"},"header":{"filename":"test-header.img"}}': LUKS payload is overlapping with the header


You need to pass some info into qcrypto_block_open to tell it that the
header is detached. Add a new enum entry to QCryptoBlockOpenFlags
perhaps.  Then skip the LUKS payload overlap check.

With regards,
Daniel
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