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/test_common.py

@@ -524,6 +524,9 @@ class CommonApkUtilsTest(unittest.TestCase):
 
 class CommonUtilsTest(unittest.TestCase):
 
+  def setUp(self):
+    self.testdata_dir = test_utils.get_testdata_dir()
+
   def tearDown(self):
     common.Cleanup()
 
@@ -730,6 +733,56 @@ class CommonUtilsTest(unittest.TestCase):
           AssertionError, common.GetSparseImage, 'system', tempdir, input_zip,
           False)
 
+  def test_GetAvbChainedPartitionArg(self):
+    pubkey = os.path.join(self.testdata_dir, 'testkey.pubkey.pem')
+    info_dict = {
+        'avb_avbtool': 'avbtool',
+        'avb_system_key_path': pubkey,
+        'avb_system_rollback_index_location': 2,
+    }
+    args = common.GetAvbChainedPartitionArg('system', info_dict).split(':')
+    self.assertEqual(3, len(args))
+    self.assertEqual('system', args[0])
+    self.assertEqual('2', args[1])
+    self.assertTrue(os.path.exists(args[2]))
+
+  def test_GetAvbChainedPartitionArg_withPrivateKey(self):
+    key = os.path.join(self.testdata_dir, 'testkey.key')
+    info_dict = {
+        'avb_avbtool': 'avbtool',
+        'avb_product_key_path': key,
+        'avb_product_rollback_index_location': 2,
+    }
+    args = common.GetAvbChainedPartitionArg('product', info_dict).split(':')
+    self.assertEqual(3, len(args))
+    self.assertEqual('product', args[0])
+    self.assertEqual('2', args[1])
+    self.assertTrue(os.path.exists(args[2]))
+
+  def test_GetAvbChainedPartitionArg_withSpecifiedKey(self):
+    info_dict = {
+        'avb_avbtool': 'avbtool',
+        'avb_system_key_path': 'does-not-exist',
+        'avb_system_rollback_index_location': 2,
+    }
+    pubkey = os.path.join(self.testdata_dir, 'testkey.pubkey.pem')
+    args = common.GetAvbChainedPartitionArg(
+        'system', info_dict, pubkey).split(':')
+    self.assertEqual(3, len(args))
+    self.assertEqual('system', args[0])
+    self.assertEqual('2', args[1])
+    self.assertTrue(os.path.exists(args[2]))
+
+  def test_GetAvbChainedPartitionArg_invalidKey(self):
+    pubkey = os.path.join(self.testdata_dir, 'testkey_with_passwd.x509.pem')
+    info_dict = {
+        'avb_avbtool': 'avbtool',
+        'avb_system_key_path': pubkey,
+        'avb_system_rollback_index_location': 2,
+    }
+    self.assertRaises(
+        AssertionError, common.GetAvbChainedPartitionArg, 'system', info_dict)
+
 
 class InstallRecoveryScriptFormatTest(unittest.TestCase):
   """Checks the format of install-recovery.sh.