block: Support detached LUKS header creation using blockdev-create

Firstly, enable the ability to choose the block device containing
a detachable LUKS header by adding the 'header' parameter to
BlockdevCreateOptionsLUKS.

Secondly, when formatting the LUKS volume with a detachable header,
truncate the payload volume to length without a header size.

Using the qmp blockdev command, create the LUKS volume with a
detachable header as follows:

1. add the secret to lock/unlock the cipher stored in the
   detached LUKS header
$ virsh qemu-monitor-command vm '{"execute":"object-add",
> "arguments":{"qom-type": "secret", "id": "sec0", "data": "foo"}}'

2. create a header img with 0 size
$ virsh qemu-monitor-command vm '{"execute":"blockdev-create",
> "arguments":{"job-id":"job0", "options":{"driver":"file",
> "filename":"/path/to/detached_luks_header.img", "size":0 }}}'

3. add protocol blockdev node for header
$ virsh qemu-monitor-command vm '{"execute":"blockdev-add",
> "arguments": {"driver":"file", "filename":
> "/path/to/detached_luks_header.img", "node-name":
> "detached-luks-header-storage"}}'

4. create a payload img with 0 size
$ virsh qemu-monitor-command vm '{"execute":"blockdev-create",
> "arguments":{"job-id":"job1", "options":{"driver":"file",
> "filename":"/path/to/detached_luks_payload_raw.img", "size":0}}}'

5. add protocol blockdev node for payload
$ virsh qemu-monitor-command vm '{"execute":"blockdev-add",
> "arguments": {"driver":"file", "filename":
> "/path/to/detached_luks_payload_raw.img", "node-name":
> "luks-payload-raw-storage"}}'

6. do the formatting with 128M size
$ virsh qemu-monitor-command c81_node1 '{"execute":"blockdev-create",
> "arguments":{"job-id":"job2", "options":{"driver":"luks", "header":
> "detached-luks-header-storage", "file":"luks-payload-raw-storage",
> "size":134217728, "preallocation":"full", "key-secret":"sec0" }}}'

Signed-off-by: Hyman Huang <yong.huang@smartx.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

block/crypto.c

@@ -162,6 +162,48 @@ block_crypto_create_init_func(QCryptoBlock *block, size_t headerlen,
     return ret;
 }
 
+static int coroutine_fn GRAPH_UNLOCKED
+block_crypto_co_format_luks_payload(BlockdevCreateOptionsLUKS *luks_opts,
+                                    Error **errp)
+{
+    BlockDriverState *bs = NULL;
+    BlockBackend *blk = NULL;
+    Error *local_error = NULL;
+    int ret;
+
+    if (luks_opts->size > INT64_MAX) {
+        return -EFBIG;
+    }
+
+    bs = bdrv_co_open_blockdev_ref(luks_opts->file, errp);
+    if (bs == NULL) {
+        return -EIO;
+    }
+
+    blk = blk_co_new_with_bs(bs, BLK_PERM_WRITE | BLK_PERM_RESIZE,
+                             BLK_PERM_ALL, errp);
+    if (!blk) {
+        ret = -EPERM;
+        goto fail;
+    }
+
+    ret = blk_truncate(blk, luks_opts->size, true,
+                       luks_opts->preallocation, 0, &local_error);
+    if (ret < 0) {
+        if (ret == -EFBIG) {
+            /* Replace the error message with a better one */
+            error_free(local_error);
+            error_setg(errp, "The requested file size is too large");
+        }
+        goto fail;
+    }
+
+    ret = 0;
+
+fail:
+    bdrv_co_unref(bs);
+    return ret;
+}
 
 static QemuOptsList block_crypto_runtime_opts_luks = {
     .name = "crypto",
@@ -341,7 +383,9 @@ static int block_crypto_open_generic(QCryptoBlockFormat format,
 static int coroutine_fn GRAPH_UNLOCKED
 block_crypto_co_create_generic(BlockDriverState *bs, int64_t size,
                                QCryptoBlockCreateOptions *opts,
-                               PreallocMode prealloc, Error **errp)
+                               PreallocMode prealloc,
+                               unsigned int flags,
+                               Error **errp)
 {
     int ret;
     BlockBackend *blk;
@@ -369,7 +413,7 @@ block_crypto_co_create_generic(BlockDriverState *bs, int64_t size,
                                   block_crypto_create_init_func,
                                   block_crypto_create_write_func,
                                   &data,
-                                  0,
+                                  flags,
                                   errp);
 
     if (!crypto) {
@@ -656,16 +700,26 @@ static int coroutine_fn GRAPH_UNLOCKED
 block_crypto_co_create_luks(BlockdevCreateOptions *create_options, Error **errp)
 {
     BlockdevCreateOptionsLUKS *luks_opts;
+    BlockDriverState *hdr_bs = NULL;
     BlockDriverState *bs = NULL;
     QCryptoBlockCreateOptions create_opts;
     PreallocMode preallocation = PREALLOC_MODE_OFF;
+    unsigned int cflags = 0;
     int ret;
 
     assert(create_options->driver == BLOCKDEV_DRIVER_LUKS);
     luks_opts = &create_options->u.luks;
 
-    if (luks_opts->file == NULL) {
-        error_setg(errp, "Formatting LUKS disk requires parameter 'file'");
+    if (luks_opts->header == NULL && luks_opts->file == NULL) {
+        error_setg(errp, "Either the parameter 'header' or 'file' must "
+                   "be specified");
+        return -EINVAL;
+    }
+
+    if ((luks_opts->preallocation != PREALLOC_MODE_OFF) &&
+        (luks_opts->file == NULL)) {
+        error_setg(errp, "Parameter 'preallocation' requires 'file' to be "
+                   "specified for formatting LUKS disk");
         return -EINVAL;
     }
 
@@ -678,22 +732,52 @@ block_crypto_co_create_luks(BlockdevCreateOptions *create_options, Error **errp)
         preallocation = luks_opts->preallocation;
     }
 
-    if (luks_opts->file) {
+    if (luks_opts->header) {
+        /* LUKS volume with detached header */
+        hdr_bs = bdrv_co_open_blockdev_ref(luks_opts->header, errp);
+        if (hdr_bs == NULL) {
+            return -EIO;
+        }
+
+        cflags |= QCRYPTO_BLOCK_CREATE_DETACHED;
+
+        /* Format the LUKS header node */
+        ret = block_crypto_co_create_generic(hdr_bs, 0, &create_opts,
+                                             PREALLOC_MODE_OFF, cflags, errp);
+        if (ret < 0) {
+            goto fail;
+        }
+
+        /* Format the LUKS payload node */
+        if (luks_opts->file) {
+            ret = block_crypto_co_format_luks_payload(luks_opts, errp);
+            if (ret < 0) {
+                goto fail;
+            }
+        }
+    } else if (luks_opts->file) {
+        /* LUKS volume with none-detached header */
         bs = bdrv_co_open_blockdev_ref(luks_opts->file, errp);
         if (bs == NULL) {
             return -EIO;
         }
 
         ret = block_crypto_co_create_generic(bs, luks_opts->size, &create_opts,
-                                             preallocation, errp);
+                                             preallocation, cflags, errp);
         if (ret < 0) {
             goto fail;
         }
     }
 
     ret = 0;
 fail:
-    bdrv_co_unref(bs);
+    if (hdr_bs != NULL) {
+        bdrv_co_unref(hdr_bs);
+    }
+
+    if (bs != NULL) {
+        bdrv_co_unref(bs);
+    }
     return ret;
 }
 
@@ -747,7 +831,8 @@ block_crypto_co_create_opts_luks(BlockDriver *drv, const char *filename,
     }
 
     /* Create format layer */
-    ret = block_crypto_co_create_generic(bs, size, create_opts, prealloc, errp);
+    ret = block_crypto_co_create_generic(bs, size, create_opts,
+                                         prealloc, 0, errp);
     if (ret < 0) {
         goto fail;
     }

qapi/block-core.json

@@ -4958,6 +4958,8 @@
 # @file: Node to create the image format on, mandatory except when
 #        'preallocation' is not requested
 #
+# @header: Block device holding a detached LUKS header. (since 9.0)
+#
 # @size: Size of the virtual disk in bytes
 #
 # @preallocation: Preallocation mode for the new image (since: 4.2)
@@ -4968,6 +4970,7 @@
 { 'struct': 'BlockdevCreateOptionsLUKS',
   'base': 'QCryptoBlockCreateOptionsLUKS',
   'data': { '*file':            'BlockdevRef',
+            '*header':          'BlockdevRef',
             'size':             'size',
             '*preallocation':   'PreallocMode' } }