Policy Settings in Chrome

Summary

Chrome exposes a different set of configurations to administrators. These configurations are called policy and they give administrators more advanced controls than the normal users. With different device management tools, administrator can deliver these polices to many users. Here is the help center article that talks about Chrome policy and its deployment.

Do I need a policy

Usually you need a policy when

  • Launching a new feature. Create a policy so that the admin can disable or enable the feature for all users.

  • Deprecate an old feature. Create a policy to give enterprise users more time to migrate away from the feature.

Adding a new policy

  1. Think carefully about the name and the desired semantics of the new policy:
    • Chose a name that is consistent with the existing naming scheme. Prefer “XXXEnabled” over “EnableXXX” because the former is more glanceable and sorts better.
    • Consider the foreseeable future and try to avoid conflicts with possible future extensions or use cases.
    • Negative policies (Disable, Disallow) are verboten because setting something to “true” to disable it confuses people.
  2. Declare the policy in the policy_templates.json
    • This file contains meta-level descriptions of all policies and is used to generated code, policy templates (ADM/ADMX for windows and the application manifest for Mac), as well as documentation.Please make sure you get the version and features flags (such as dynamic_refresh and supported_on) right.
    • Here are the most used attributes. Please note that, all attributes below other than supported_on do not change the code behavior.
      • supported_on: It controls the platform and Chrome milestone the policy supports.
      • dynamic_refresh: It tells admin if the policy value can be changed and taken affected without re-launch Chrome.
      • per_profile: It tells the admin if different policy value can be assigned to different profile.
      • can_be_recommended: It tells the admin if they can set the policy in the recommended level and allow user override it with UI, command line switch or extension.
      • future: It hides the policy from auto-generated templates and documentation. It's used when your policy needs multiple milestone development.
    • The complete list of attributes and their expected values can be found in the policy_templates.json.
    • The textual policy description should include the following:
      • What features of Chrome are affected.
      • Which behavior and/or UI/UX changes the policy triggers.
      • How the policy behaves if it‘s left unset or set to invalid/default values. This may seem obvious to you, and it probably is. However, this information seems to be provided for Windows Group Policy traditionally, and we’ve seen requests from organizations to explicitly spell out the behavior for all possible values and for when the policy is unset.
  3. Create a preference and map the policy value to it.
    • All policy values need to be mapped into a prefs value before being used unless the policy is needed before PrefService initialization.
    • To map the policy:
      1. Create a prefs and register the prefs in Local State or Profile Prefs. Please note that, this must match the per_profile attribute in the policy_templates.json. We also strongly encourage developers to register the prefs with Profile Prefs if possible, because this gives admin more flexiability of policy setup.
      2. Most of policies can be mapped to prefs with kSimplePolicyMap in configuration_policy_handler_list_factory.cc. If the policy needs additional verification or processing, please implement a ConfigurationPolicyHandler to do so.
      3. Test the mapping by adding policy to policy_test_cases.json
  4. Disable the user setting UI when the policy is applied.
    • If your feature can be controlled by GUI in chrome://settings, the associated option should be disabled when the policy controlling it is managed.
      • PrefService:Preference::IsManaged reveals whether a prefs value comes from policy or not.
      • The setting needs an indicator to tell users that the setting is enforced by the administrator.
  5. Support dynamic_refresh if possible.
    • We strongly encourage developers to make their policies support this attribute. It means admin can change the policy value and Chrome will honor the change at run-time wihtout requiring a restart of the browser.
    • Chrome OS does not support non-dynamic user policies.
    • Most of time, this requires a PrefChangeRegistrar to listen to the preference change notification. And update UI or browser behavior right a way.
  6. Adding a device policy for Chrome OS.
    • Most of policies that are used by browser can be shared by desktop and Chrome OS. However, you need few additional steps for device policy on Chrome OS.
      • Add a message for your policy in components/policy/proto/chrome_device_policy.proto. Please note that all proto fields are optional.
      • Update chrome/browser/chromeos/policy/device_policy_decoder_chromeos.{h,cc} for the new policy.
  7. Test the policy.
    • Add a test to verify the policy. You can add a test in chrome/browser/policy/<area>_policy_browsertest.cc or with the policy implementation. For example, a network policy test can be put into chrome/browser/net. Ideally, your test would set the policy, fire up the browser, and interact with the browser just as a user would do to check whether the policy takes effect.
  8. Manually testing your policy.
    • Windows: The simplest way to test is to write the registry keys manually to Software\Policies\Chromium (for Chromium builds) or Software\Policies\Google\Chrome (for Google Chrome branded builds). If you want to test policy refresh, you need to use group policy tools and gpupdate; see Windows Quick Start.
    • Mac: See Mac Quick Start (section “Debugging”)
    • Linux: See Linux Quick Start (section “Set Up Policies”)
    • Chrome OS and Android are more complex to test, as a full end-to-end test requires network transactions to the policy test server. Instructions for how to set up the policy test server and have the browser talk to it are here: Running the cloud policy test server. If you'd just like to do a quick test for Chrome OS, the Linux code is also functional on CrOS, see Linux Quick Start.
  9. If you are adding a new policy that supersedes an older one, verify that the new policy works as expected even if the old policy is set (allowing us to set both during the transition time when Chrome versions honoring the old and the new policies coexist).
  10. If your policy has interactions with other policies, make sure to document, test and cover these by automated tests.

Examples

Here is an example based on the instruction above. It's a good, simple place to get started: https://chromium-review.googlesource.com/c/chromium/src/+/1742209

Modifying existing policies

If you are planning to modify an existing policy, please send out a one-pager to client- and server-side stakeholders explaining the planned change.

There are a few noteworthy pitfalls that you should be aware of when updating code that handles existing policy settings, in particular:

  • Make sure the policy meta data is up-to-date, in particular supported_on, and the feature flags.
  • In general, don‘t change policy semantics in a way that is incompatible (as determined by user/admin-visible behavior) with previous semantics. **In particular, consider that existing policy deployments may affect both old and new browser versions, and both should behave according to the admin’s intentions**.
  • An important pitfall is that adding an additional allowed value to an enum policy may cause compatibility issues. Specifically, an administrator may use the new policy value, which makes older Chrome versions that may still be deployed (which don't understand the new value) fall back to the default behavior. Carefully consider if this is OK in your case. Usually, it is preferred to create a new policy with the additional value and deprecate the old one.
  • Don't rely on the cloud policy server for policy migrations because this has been proven to be error prone. To the extent possible, all compatibility and migration code should be contained in the client.
  • It is OK to expand semantics of policy values as long as the previous policy description is compatible with the new behavior (see the “extending enum” pitfall above however).
  • It is OK to update feature implementations and the policy description when Chrome changes as long as the intended effect of the policy remains intact.
  • The process for removing policies is to deprecate them first, wait a few releases (if possible) and then drop support for them. Make sure you put the deprecated flag if you deprecate a policy.

Presubmit Checks when Modifying Existing Policies

To enforce the above rules concerning policy modification and ensure no backwards incompatible changes are introduced, there will be presubmit checks performed on every change to policy_templates.json.

The presubmit checks perform the following verifications:

  1. It verifies if a policy is considered un-released before allowing a change. A policy is considered un-released if any of the following conditions are true:

    1. Is the unchanged policy marked as future: true.
    2. All the supported_versions of the policy satisfy any of the following conditions
      1. The unchanged supported major version is >= the current major version stored in the VERSION file at tip of tree. This covers the case of a policy that was just recently been added but has not yet been released to a stable branch.
      2. The changed supported version == unchanged supported version + 1 and the changed supported version is equal to the version stored in the VERSION file at tip of tree. This check covers the case of “un-releasing” a policy after a new stable branch has been cut but before a new stable release has rolled out. Normally such a change should eventually be merged into the stable branch before the release.

  2. If the policy is considered un-released, all changes to it are allowed.

  3. However if the policy is not un-released then the following verifications are performed on the delta between the original policy and the changed policy.

    1. Released policies cannot be removed.
    2. Released policies cannot have their type changed (e.g. from bool to Enum).
    3. Released policies cannot have the future: true flag added to it. This flag can only be set on a new policy.
    4. Released policies can only add additional supported_on versions. They cannot remove or modify existing values for this field except for the special case above for determining if a policy is released. Policy support end version (adding “-xx” ) can however be added to the supported_on version to specify that a policy will no longer be supported going forward (as long as the initial supported_on version is not changed).
    5. Released policies cannot be renamed (this is the equivalent of a delete + add).
    6. Released policies cannot change their device_only flag. This flag can only be set on a new policy.
    7. Released policies with non dict types cannot have their schema changed.
      1. For enum types this means values cannot be renamed or removed (these should be marked as deprecated instead).
      2. For int types, we will allow making the minimum and maximum values less restrictive than the existing values.
      3. For string types, we will allow the removal of the “pattern” property to allow the validation to be less restrictive.
      4. We will allow addition to any list type values only at the end of the list of values and not in the middle or at the beginning (this restriction will cover the list of valid enum values as well).
      5. These same restrictions will apply recursively to all property schema definitions listed in a dictionary type policy.
    8. Released dict policies cannot remove and modify any existing key in their schema. They can only add new keys to the schema.
      1. Dictionary policies can have some of their “required” fields removed in order to be less restrictive.

Cloud Policy

For googlers only: Cloud Policy will be maintained by the Admin console team, see instruction here about updating the cloud policy.

Post policy update

Once the policy is added or modified, there is nothing else needs to be taken care of by the Chromium developers. However, there are few things will be updated based on the json file. Please note that, there is to ETA for everything listed below.

Additional Notes

  1. policy_templates.json is actually a python dictionary even the file name contains json.