Add a skeleton sepolicy compat generator

sepolicy_generate_compat will be used to generate compat files for ToT,
based on the mapping file from aosp_arm64-userdebug target of {ver}
source tree. For now, it only supports downloading a mapping file
system/etc/selinux/mapping/{ver}.cil from the Android build server.

Bug: 214336258
Test: sepolicy_generate_compat --branch sc-v2-dev --version 32.0
Change-Id: I48043c71a6866aa385ecd67462f7678561cc5a38

tools/Android.bp

@@ -63,3 +63,8 @@ python_binary_host {
     name: "insertkeys",
     srcs: ["insertkeys.py"],
 }
+
+python_binary_host {
+    name: "sepolicy_generate_compat",
+    srcs: ["sepolicy_generate_compat.py"],
+}

tools/sepolicy_generate_compat.py

@@ -0,0 +1,138 @@
+#!/usr/bin/env python3
+
+# Copyright 2022 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import argparse
+import glob
+import logging
+import os
+import shutil
+import subprocess
+import tempfile
+import zipfile
+"""This tool generates a mapping file for {ver} core sepolicy."""
+
+
+def check_run(cmd):
+    logging.debug('Running cmd: %s' % cmd)
+    subprocess.run(cmd, check=True)
+
+
+def check_output(cmd):
+    logging.debug('Running cmd: %s' % cmd)
+    return subprocess.run(cmd, check=True, stdout=subprocess.PIPE)
+
+
+def fetch_artifact(branch, build, pattern, destination='.'):
+    """Fetches build artifacts from Android Build server.
+
+    Args:
+      branch: string, branch to pull build artifacts from
+      build: string, build ID or "latest"
+      pattern: string, pattern of build artifact file name
+      destination: string, destination to pull build artifact to
+    """
+    fetch_artifact_path = '/google/data/ro/projects/android/fetch_artifact'
+    cmd = [
+        fetch_artifact_path, '--branch', branch, '--target',
+        'aosp_arm64-userdebug'
+    ]
+    if build == 'latest':
+        cmd.append('--latest')
+    else:
+        cmd.extend(['--bid', build])
+    cmd.extend([pattern, destination])
+    check_run(cmd)
+
+
+def extract_mapping_file_from_img(img_path, ver, destination='.'):
+    """ Extracts system/etc/selinux/mapping/{ver}.cil from system.img file.
+
+    Args:
+      img_path: string, path to system.img file
+      ver: string, version of designated mapping file
+      destination: string, destination to pull the mapping file to
+    """
+
+    cmd = [
+        'debugfs', '-R',
+        'cat system/etc/selinux/mapping/%s.cil' % ver, img_path
+    ]
+    with open(os.path.join(destination, '%s.cil' % ver), 'wb') as f:
+        logging.debug('Extracting %s.cil to %s' % (ver, destination))
+        f.write(check_output(cmd).stdout)
+
+
+def download_mapping_file(branch, build, ver, destination='.'):
+    """ Downloads system/etc/selinux/mapping/{ver}.cil from Android Build server.
+
+    Args:
+      branch: string, branch to pull build artifacts from (e.g. "sc-v2-dev")
+      build: string, build ID or "latest"
+      ver: string, version of designated mapping file (e.g. "32.0")
+      destination: string, destination to pull build artifact to
+    """
+    temp_dir = tempfile.mkdtemp()
+
+    try:
+        artifact_pattern = 'aosp_arm64-img-*.zip'
+        fetch_artifact(branch, build, artifact_pattern, temp_dir)
+
+        # glob must succeed
+        zip_path = glob.glob(os.path.join(temp_dir, artifact_pattern))[0]
+        with zipfile.ZipFile(zip_path) as zip_file:
+            logging.debug('Extracting system.img to %s' % temp_dir)
+            zip_file.extract('system.img', temp_dir)
+
+        system_img_path = os.path.join(temp_dir, 'system.img')
+        extract_mapping_file_from_img(system_img_path, ver, destination)
+    finally:
+        logging.info('Deleting temporary dir: {}'.format(temp_dir))
+        shutil.rmtree(temp_dir)
+
+
+def get_args():
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        '--branch',
+        required=True,
+        help='Branch to pull build from. e.g. "sc-v2-dev"')
+    parser.add_argument('--build', required=True, help='Build ID, or "latest"')
+    parser.add_argument(
+        '--version',
+        required=True,
+        help='Version of designated mapping file. e.g. "32.0"')
+    parser.add_argument(
+        '-v',
+        '--verbose',
+        action='count',
+        default=0,
+        help='Increase output verbosity, e.g. "-v", "-vv".')
+    return parser.parse_args()
+
+
+def main():
+    args = get_args()
+
+    verbosity = min(args.verbose, 2)
+    logging.basicConfig(
+        format='%(levelname)-8s [%(filename)s:%(lineno)d] %(message)s',
+        level=(logging.WARNING, logging.INFO, logging.DEBUG)[verbosity])
+
+    download_mapping_file(args.branch, args.build, args.version)
+
+
+if __name__ == '__main__':
+    main()