Fix the signing error in gsi_arm64 builds

After adding 'PREBUILT_IMAGES/pvmfw.img' into gsi_arm64,
the signing process fails:

common.ExternalError: Failed to run command
  '['avbtool', 'extract_public_key', '--key', 'PRESIGNED',
    '--output', '/tmp/avb-8z8y8_xn.avbpubkey']' (exit code 1):
  ~/codebase/android15-tests-dev/otatools/bin/avbtool:
    Error getting public key: b'Could not open file or uri for loading
    private key of public key from PRESIGNED: No such file or directory\n'

This is because that apex files are pre-signed in gsi_arm64
and the script currently tries to extract public key from the
non-existing 'PRESIGNED' file.

Fix this by obtaining the public key from 'apex_pubkey' of
'SYSTEM/apex/com.android.virt.apex'.

See https://source.android.com/docs/core/ota/apex#apex-format
for details.

Bug: 384813199
Test: m sign_target_files_apks
Test: sign_target_files_apks --allow_gsi_debug_sepolicy \
        --extra_apex_payload_key com.android.virt.apex= \
        -e com.android.virt.apex= \
        gsi_arm64-target_files-${build_id}.zip signed.zip
Test: `zipinfo signed.zip | grep pvmfw`, checks pvmfw.img is included.
Change-Id: I551e14fa6a0c63e3cef334b953f670cf9c465e10
diff --git a/tools/releasetools/sign_target_files_apks.py b/tools/releasetools/sign_target_files_apks.py
index 4ad97e0..2378539 100755
--- a/tools/releasetools/sign_target_files_apks.py
+++ b/tools/releasetools/sign_target_files_apks.py
@@ -862,21 +862,32 @@
 
     # Updates pvmfw embedded public key with the virt APEX payload key.
     elif filename == "PREBUILT_IMAGES/pvmfw.img":
-      # Find the name of the virt APEX in the target files.
+      # Find the path of the virt APEX in the target files.
       namelist = input_tf_zip.namelist()
-      apex_gen = (GetApexFilename(f) for f in namelist if IsApexFile(f))
-      virt_apex_re = re.compile("^com\.([^\.]+\.)?android\.virt\.apex$")
-      virt_apex = next((a for a in apex_gen if virt_apex_re.match(a)), None)
-      if not virt_apex:
+      apex_gen = (f for f in namelist if IsApexFile(f))
+      virt_apex_re = re.compile("^.*com\.([^\.]+\.)?android\.virt\.apex$")
+      virt_apex_path = next(
+        (a for a in apex_gen if virt_apex_re.match(a)), None)
+      if not virt_apex_path:
         print("Removing %s from ramdisk: virt APEX not found" % filename)
       else:
-        print("Replacing %s embedded key with %s key" % (filename, virt_apex))
+        print("Replacing %s embedded key with %s key" % (filename,
+                                                         virt_apex_path))
         # Get the current and new embedded keys.
+        virt_apex = GetApexFilename(virt_apex_path)
         payload_key, container_key, sign_tool = apex_keys[virt_apex]
-        new_pubkey_path = common.ExtractAvbPublicKey(
-            misc_info['avb_avbtool'], payload_key)
-        with open(new_pubkey_path, 'rb') as f:
-          new_pubkey = f.read()
+
+        # b/384813199: handles the pre-signed com.android.virt.apex in GSI.
+        if payload_key == 'PRESIGNED':
+          with input_tf_zip.open(virt_apex_path) as apex_fp:
+            with zipfile.ZipFile(apex_fp) as apex_zip:
+              new_pubkey = apex_zip.read('apex_pubkey')
+        else:
+          new_pubkey_path = common.ExtractAvbPublicKey(
+              misc_info['avb_avbtool'], payload_key)
+          with open(new_pubkey_path, 'rb') as f:
+            new_pubkey = f.read()
+
         pubkey_info = copy.copy(
             input_tf_zip.getinfo("PREBUILT_IMAGES/pvmfw_embedded.avbpubkey"))
         old_pubkey = input_tf_zip.read(pubkey_info.filename)