|
From: | Yong Huang |
Subject: | Re: [v2 3/4] crypto: Support generic LUKS encryption |
Date: | Mon, 18 Dec 2023 22:15:34 +0800 |
On Thu, Dec 07, 2023 at 12:37:44AM +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>
> ---
> block/crypto.c | 38 +++++++++++++++++++++++++++++++++++++-
> 1 file changed, 37 insertions(+), 1 deletion(-)
>
> diff --git a/block/crypto.c b/block/crypto.c
> index f82b13d32b..7d70349463 100644
> --- a/block/crypto.c
> +++ b/block/crypto.c
> @@ -40,6 +40,7 @@ struct BlockCrypto {
> QCryptoBlock *block;
> bool updating_keys;
> BdrvChild *header; /* Reference to the detached LUKS header */
> + bool detached_mode; /* If true, LUKS plays a detached header role */
> };
>
>
> @@ -64,12 +65,16 @@ 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);
> + if (crypto->detached_mode)
> + ret = bdrv_pread(crypto->header, offset, buflen, buf, 0);
> + else
> + ret = bdrv_pread(bs->file, offset, buflen, buf, 0);
This can be simplified to:
ret = bdrv_pread(bs->header ? bs->header : file, offset, buflen, buf, 0);
> if (ret < 0) {
> error_setg_errno(errp, -ret, "Could not read encryption header");
> return ret;
> @@ -269,6 +274,8 @@ static int block_crypto_open_generic(QCryptoBlockFormat format,
> QCryptoBlockOpenOptions *open_opts = NULL;
> unsigned int cflags = 0;
> QDict *cryptoopts = NULL;
> + const char *header_bdref =
> + qdict_get_try_str(options, "header");
>
> GLOBAL_STATE_CODE();
>
> @@ -277,6 +284,16 @@ static int block_crypto_open_generic(QCryptoBlockFormat format,
> return ret;
> }
>
> + if (header_bdref) {
> + crypto->detached_mode = true;
Drop this flag since it has no benefit.
> + crypto->header = bdrv_open_child(NULL, options, "header", bs,
> + &child_of_bds, BDRV_CHILD_METADATA,
> + false, errp);
> + if (!crypto->header) {
> + return -EINVAL;
> + }
> + }
> +
> GRAPH_RDLOCK_GUARD_MAINLOOP();
>
> bs->supported_write_flags = BDRV_REQ_FUA &
> @@ -312,6 +329,14 @@ static int block_crypto_open_generic(QCryptoBlockFormat format,
> goto cleanup;
> }
>
> + if (crypto->detached_mode) {
if (crypto->header != NULL)
> + /*
> + * Set payload offset to zero as the file bdref has no LUKS
> + * header under detached mode.
> + */
> + qcrypto_block_set_payload_offset(crypto->block, 0);
The LUKS header stores the payload offset. If someone creates the LUKS
volume with a detached header, they may still choose to put the payload
at a non-zero offset.
So AFAICT, we should always honour the payload offset from the header,
even when detached. When formatting the header, we should default to
a zero offset though
> + }
> +
> bs->encrypted = true;
>
> ret = 0;
> @@ -903,6 +928,17 @@ block_crypto_child_perms(BlockDriverState *bs, BdrvChild *c,
>
> BlockCrypto *crypto = bs->opaque;
>
> + if (role == (role & BDRV_CHILD_METADATA)) {
> + /* Assign read permission only */
> + perm |= BLK_PERM_CONSISTENT_READ;
> + /* Share all permissions */
> + shared |= BLK_PERM_ALL;
> +
> + *nperm = perm;
> + *nshared = shared;
> + return;
> + }
What is code doing ? You've set BDRV_CHILD_METADATA role on the
crypto->header object, but how does this block_crypto_child_perms
method get run against crypto->header ?
> +
> bdrv_default_perms(bs, c, role, reopen_queue, perm, shared, nperm, nshared);
>
> /*
> --
> 2.39.1
>
With regards,
Daniel
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