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, an 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.

  • Deprecating 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:
    • Choose 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 generate 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 feature 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, future_on' anddefault_for_enterprise_users` do not change the code behavior.
      • supported_on and future_on: They control the platforms that the policy supports. supported_on is used for released platforms with milestone range while future_on is used for unreleased platforms. See Launch a policy below for more information.
      • default_for_enterprise_users: Its value is applied as a mandatory policy for managed users on Chrome OS unless a different setting is explicitly set.
      • dynamic_refresh: It tells the admin whether the policy value can be changed and take effect without re-launching Chrome.
      • per_profile: It tells the admin whether different policy values can be assigned to different profiles.
      • can_be_recommended: It tells the admin whether they can mark the policy as recommended and allow the user to override it in the UI, using a command line switch or an extension.
    • 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.
    • See description_guidelines.md for additional guidelines when creating a description, including how various products should be referenced.
  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 flexibility of policy setup.
      2. Most 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 (see instructions).
      4. iOS platform has its own configuration_policy_handler_list_factory.mm and policy_test_cases.json file.
  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 the admin can change the policy value and Chrome will honor the change at run-time without requiring a restart of the browser. Chrome OS does not always support non-dynamic profile policies. Please verify with a Chrome OS policy owner if your profile policy does not support dynamic refresh on Chrome OS.
    • Most of the time, this requires a PrefChangeRegistrar to listen to the preference change notification and update UI or browser behavior right away.
  6. Adding a device policy for Chrome OS.
    • Most policies that are used by the browser can be shared between desktop and Chrome OS. However, you need a few additional steps for a 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/ash/policy/core/device_policy_decoder.{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 on 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.

Launch a policy

  1. When adding a new policy, put the platforms it will be supported in the future_on list.
    • The policy is hidden from any auto-generated template or documentation on those platforms.
    • The policy will also be unavailable on Beta and Stable channel unless it's enabled specifically by EnableExperimentalPolicies policy.
  2. Implement the policy, get launch approval if necessary.
  3. If the policy needs to be tested with small set of users first, keep the platforms in the future_on list and running the tester program with the EnableExperimentalPolicies policy.
  4. Move the launched platforms from future_on to supported_on and set the ‘since_version’ of those platforms to the milestone for which the launch approval was granted.
  5. If the ‘since_version’ is set to a earlier milestone, you need to merge back all necessary commits.

Do not use finch to control policy launch process.

Policies are inherently switches that admins will turn on if they need. Getting inconsistent behavior based on factors outside of their control only causes confusion and is source for support requests. Use the step 3 above if the policy needs external testers before being officially announced.

Deprecating a policy

A policy is deprecated when admins should stop using it. This is often because a new policy was been released that should be used instead.

When marking a policy as deprecated, it still needs to work the same as before in Chrome. If you wish to remove the functionality, you'll need to changed the supported_on field. See “Removing support for a policy” below for more details.

Steps

  1. Update policy_templates.json, marking the policy as deprecated and updating the description to describe when and why the policy as deprecated and what admins should be doing instead.
  2. Update the policy handling code. This is generally ensuring that if the old policy is set, the values are propagated to the new policies if they were unset.
  3. Notify chromium-enterprise@chromium.org to ensure this deprecation is mentioned in the enterprise release notes.

Removing support for a policy

Generally speaking, policies shouldn't be removed from Chrome. Although they can be deprecated fairly easily, removing support for a policy is a much bigger issue, because admins might be relying on that functionality.

The two main reasons for removing support for a policy are:

  1. It was a policy that was always documented as having a limited lifespan, such as an escape hatch policy.
  2. The feature this policy impacts was removed from Chrome.

If the policy was never launched, it can also be deleted from policy_templates.json instead of just being marked as no longer supported. In this case, please remember to add the deleted id to deleted_policy_ids.

If you want to remove support for another reason, please reach out to someone in ENTERPRISE_POLICY_OWNERS to ensure this is okay. The general preference is to leave policies as deprecated, but still supported.

When removing support for a policy, update supported_on to correctly list the last milestone the policy is supported on. Please also set ‘deprecated’ to True if the policy skipped past the deprecation state.

Steps

  1. Update policy_templates.json, marking the policy as no longer supported. Also marking as deprecated if not previously done.
  2. Update the related test in the policy_test_cases.json.
    • If the policy is going to be removed in the current milestone, remove the the test at the same time.
    • If the policy is going to be removed in the future milestone, remove the test after policy support ended.
  3. Remove the policy handling code.
  4. Notify chromium-enterprise@chromium.org to ensure this removal of support is mentioned in the enterprise release notes.

Examples

Here is an example based on the instructions 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 the code that handles existing policy settings, in particular:

  • Make sure the policy metadata 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 (and 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, presubmit checks will be performed on every change to policy_templates.json.

The presubmit checks perform the following verifications:

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

    1. It is an 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 has 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 “unreleasing” 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.
    3. supported_on list is empty.
  2. If the policy is considered unreleased, all changes to it are allowed.

  3. However if the policy is 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 or modify any existing keys 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.
  4. A policy is partially released if both supported_on and future_on list are not empty.

  5. The partially released policy is considered as a released policy and only the future_on list can be modified freely. However, any platform in the supported_on list cannot be moved back to the future_on list.

Cloud Policy

For Googlers only: The Cloud Policy will be maintained by the Admin console team. See instructions here on how to update the Cloud Policy.

Post policy update

Once the policy is added or modified, nothing else needs to be taken care of by the Chromium developers. However, there are a few things that will be updated based on the json file. Please note that there is no ETA for everything listed below.

Targeting features at commercial users

The recommended method to target commercial users is to create a policy to control the behavior of a feature. You can for example create a feature only for consumer users by setting default_for_enterprise_users to false; however, it should only be used when the default enterprise behavior should be different than regular consumer behavior.


Additional Notes

  1. policy_templates.json is actually a Python dictionary even though the file name contains json.
  2. The future_on flag can disable policy on Beta of Stable channel only if the policy value is copied to PrefService in Step 3 of Adding a new policy.