Privileged Permission Allowlisting

Privileged apps are system apps that are located in a priv-app directory on one of the system image partitions. The partitions used for Android releases are

  • Android 8.1 and lower - /system
  • Android 9 and higher - /system, /product, /vendor

Throughout this page, /etc/permissions/priv-app resolves to partition/etc/permissions/priv-app.

Historically, device manufacturers had little control over which signature|privileged permissions could be granted to privileged apps. Starting in Android 8.0, manufacturers must explicitly grant privileged permissions in the system configuration XML files in the /etc/permissions directory. As of Android 9, implementors must explicitly grant or deny all privileged permissions or the device won’t boot.

The privapp-permissions.xml file can only grant or deny permissions for privileged apps on the same partition. For example, if an app on the /product partition requests privileged permissions, the request can only be granted or denied by a privapp-permissions.xml file that’s also on /product.

Adding allowlists

Permission allowlists for apps can be listed in a single XML or in multiple XML files located in the frameworks/base/etc/permissions directory as follows:

  • /etc/permissions/privapp-permissions-OEM_NAME.xml
  • /etc/permissions/privapp-permissions-DEVICE_NAME.xml

There is no strict rule for organizing content. Device implementers can determine content structure as long as all apps from /system/priv-app are allowlisted. For example, Google has a single allowlist for all privileged apps developed by Google, and recommends the following organization:

  • Permissions for apps that are already included in the Android Open Source Project (AOSP) tree are listed in /etc/permissions/privapp-permissions-platform.xml.
  • Permissions for Google apps are listed in /etc/permissions/privapp-permissions-google.xml.
  • For other apps, use files of the form: /etc/permissions/privapp-permissions-DEVICE_NAME.xml.

Customizing allowlists

AOSP includes an allowlist implementation that can be customized as needed. Permissions for apps included in AOSP are already allowlisted in /etc/permissions/privapp-permissions-platform.xml.

If there are permissions that should be denied, edit the XML to use a "deny-permission" tag instead of a "permission" tag. Example: 

<!-- This XML file declares which signature|privileged permissions to grant to
privileged apps that come with the platform -->

    <permissions>
    <privapp-permissions package="com.android.backupconfirm">
    <permission name="android.permission.BACKUP"/>
    <permission name="android.permission.CRYPT_KEEPER"/>
    </privapp-permissions>

    <privapp-permissions package="com.android.cellbroadcastreceiver">

    <!-- Don't allow the application to interact across users -->

    <deny-permission name="android.permission.INTERACT_ACROSS_USERS"/>
    <permission name="android.permission.MANAGE_USERS"/>
    <permission name="android.permission.MODIFY_PHONE_STATE"/>
    <permission name="android.permission.READ_PRIVILEGED_PHONE_STATE"/>
    <permission name="android.permission.RECEIVE_EMERGENCY_BROADCAST"/>
    </privapp-permissions>
    ...

Finding missing permissions

To find missing permissions when bringing up a new device, enable transitional log mode: 

ro.control_privapp_permissions=log

Violations are reported in the log file, but nonprivileged permissions are still granted. This keeps the device in a working state while providing the list of violations. This is the error message format: 

PackageManager: Privileged permission {PERMISSION_NAME} for package {PACKAGE_NAME} - not in privapp-permissions allowlist

All violations must be addressed by adding the missing permissions to the appropriate allowlists.

  • On Android 8.0 and lower, the affected apps aren’t granted the missing permissions even if they are in the priv-app path.
  • On Android 9 and higher, violations (of privileged permissions) mean the device doesn’t boot. You must explicitly either allow or deny all privileged permissions

Enforcing allowlists

After allowlists are in place, enable runtime enforcement by setting the build property ro.control_privapp_permissions=enforce.