Also install verity_key to ramdisk for non-system-as-root target.

The commit in d14b895665
(https://android-review.googlesource.com/c/platform/build/+/728287)
changed partition layout, to always build the root dir into system.img,
even for devices not using system-as-root (i.e. the ones with separate
boot ramdisk).

With the new layout, there will be two root dirs for non-system-as-root
targets during the boot. If such a device uses Verified Boot 1.0,
/verity_key needs to be available in both roots, to establish the chain
of trust.
 - bootloader uses the baked-in key to verify boot.img; it then loads
   the ramdisk from the verified boot.img
 - First stage init uses /verity_key (in ramdisk) to verify and mount
   system.img at /system, then chroot's to it
 - Second stage init uses /verity_key (in system.img) to verify and
   mount other partitions

This CL adds rules to additionally install verity_key into ramdisk for
such targets.

Bug: 139770257
Test: Set up a target to use non-system-as-root
      (BOARD_BUILD_SYSTEM_ROOT_IMAGE != true). `m dist`.
Test: Check that both ROOT/verity_key and BOOT/RAMDISK/verity_key exist
      in the built target_files.zip.
Test: Run validate_target_files to validate the above target_files.zip.
      $ validate_target_files \
          --verity_key_mincrypt /path/to/verity_key \
          target_files.zip
Test: Run sign_target_files_apks to sign the above target. Re-run
      validate_target_files on the signed target_files.zip.
Test: python -m unittest test_validate_target_files
Change-Id: Ibe7e771c8c376429add85851ac86055564765d3c

tools/releasetools/validate_target_files.py

@@ -276,15 +276,12 @@ def ValidateVerifiedBootImages(input_tmp, info_dict, options):
   # Verify verity signed system images in Verified Boot 1.0. Note that not using
   # 'elif' here, since 'boot_signer' and 'verity' are not bundled in VB 1.0.
   if info_dict.get('verity') == 'true':
-    # First verify that the verity key that's built into the root image (as
-    # /verity_key) matches the one given via command line, if any.
-    if info_dict.get("system_root_image") == "true":
-      verity_key_mincrypt = os.path.join(input_tmp, 'ROOT', 'verity_key')
-    else:
-      verity_key_mincrypt = os.path.join(
-          input_tmp, 'BOOT', 'RAMDISK', 'verity_key')
+    # First verify that the verity key is built into the root image (regardless
+    # of system-as-root).
+    verity_key_mincrypt = os.path.join(input_tmp, 'ROOT', 'verity_key')
     assert os.path.exists(verity_key_mincrypt), 'Missing verity_key'
 
+    # Verify /verity_key matches the one given via command line, if any.
     if options['verity_key_mincrypt'] is None:
       logging.warn(
           'Skipped checking the content of /verity_key, as the key file not '
@@ -295,6 +292,18 @@ def ValidateVerifiedBootImages(input_tmp, info_dict, options):
           "Mismatching mincrypt verity key files"
       logging.info('Verified the content of /verity_key')
 
+    # For devices with a separate ramdisk (i.e. non-system-as-root), there must
+    # be a copy in ramdisk.
+    if info_dict.get("system_root_image") != "true":
+      verity_key_ramdisk = os.path.join(
+          input_tmp, 'BOOT', 'RAMDISK', 'verity_key')
+      assert os.path.exists(verity_key_ramdisk), 'Missing verity_key in ramdisk'
+
+      assert filecmp.cmp(
+          verity_key_mincrypt, verity_key_ramdisk, shallow=False), \
+              'Mismatching verity_key files in root and ramdisk'
+      logging.info('Verified the content of /verity_key in ramdisk')
+
     # Then verify the verity signed system/vendor/product images, against the
     # verity pubkey in mincrypt format.
     for image in ('system.img', 'vendor.img', 'product.img'):