releasetools: Support verifying AVB signed images with chained partitions.

For example, verify a target_files.zip that has system AVB-signed as a
chained partition.

  $ build/make/tools/releasetools/validate_target_files.py \
      signed-target_files-4904652.zip \
      --verity_key verifiedboot_pub.pem \
      --avb_system_key_path system_pub.pem

Note that verifiedboot_pub.pem should be the key (either public or
private) to verify vbmeta.img, and 'system_pub.pem' should be the key
(either public or private) for the chained partition of system.

testdata/testkey.key is the private key converted from
testdata/testkey.pk8 for testing purpose (`openssl pkcs8 -in
testdata/testkey.pk8 -inform DER -out testdata/testkey.key -nocrypt`).

Bug: 63706333
Test: python -m unittest test_common
Test: python -m unittest test_add_img_to_target_files
Test: `m dist` on aosp_walleye-userdebug; Run validate_target_files.py
      on the generated target_files.zip.
Test: Set up walleye with chained system partition; `m dist`; Run
      validate_target_files.py on the generated target_files.zip.
Change-Id: I38517ab39baf8a5bc1a6062fab2fe229b68e897d

tools/releasetools/validate_target_files.py

@@ -315,9 +315,19 @@ def ValidateVerifiedBootImages(input_tmp, info_dict, options):
     key = options['verity_key']
     if key is None:
       key = info_dict['avb_vbmeta_key_path']
+
     # avbtool verifies all the images that have descriptors listed in vbmeta.
     image = os.path.join(input_tmp, 'IMAGES', 'vbmeta.img')
     cmd = ['avbtool', 'verify_image', '--image', image, '--key', key]
+
+    # Append the args for chained partitions if any.
+    for partition in common.AVB_PARTITIONS:
+      key_name = 'avb_' + partition + '_key_path'
+      if info_dict.get(key_name) is not None:
+        chained_partition_arg = common.GetAvbChainedPartitionArg(
+            partition, info_dict, options[key_name])
+        cmd.extend(["--expected_chain_partition", chained_partition_arg])
+
     proc = common.Run(cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
     stdoutdata, _ = proc.communicate()
     assert proc.returncode == 0, \
@@ -339,8 +349,13 @@ def main():
   parser.add_argument(
       '--verity_key',
       help='the verity public key to verify the bootable images (Verified '
-           'Boot 1.0), or the vbmeta image (Verified Boot 2.0), where '
+           'Boot 1.0), or the vbmeta image (Verified Boot 2.0, aka AVB), where '
            'applicable')
+  for partition in common.AVB_PARTITIONS:
+    parser.add_argument(
+        '--avb_' + partition + '_key_path',
+        help='the public or private key in PEM format to verify AVB chained '
+             'partition of {}'.format(partition))
   parser.add_argument(
       '--verity_key_mincrypt',
       help='the verity public key in mincrypt format to verify the system '