Security Policy

Overview

Security policies define a combination of runtime and compile time restrictions that apply to a particular build type.

This directory contains a base security policy that may be merged into product specific policies for any build type (_user, _userdebug, _eng), as well as additional policies for _eng builds.

This directory is split up into:

• component_manager_policy_base.json5: The base policies that are reused in all product configurations.
• component_manager_policy.json5: For restricting V2 (.cml) capabilities at runtime & compile time. This file is combined with component_manager_policy_base.json5 for products defined in fuchsia.git.
• subsystems/: Contains component manager policy for platform subsystems included by products' platform Assembly configuration.
• build/: For build time verification configuration such as policy exception, verifying goldens & structured configuration.
• pkgfs/: For the set of pkgfs allowlists.
• zxcrypt: For the configuration type of the block encryption driver. Whether we use a null key (for testing) or the TEE keysafe implementation.

Component V2 (.cml) Protocol Restriction

You will want to add your new protocol to //src/security/component_manager_policy.json5.

This file is compiled into the Zircon Boot Image (ZBI) at the path: /boot/config/component_manager. Any protocols listed in this file will be restricted to route only to the set of target_monikers provided. All other routes will be dropped. Scrutiny will additionally verify at build time that the security policy is enforced for all build types with verifier enable. This provides a very powerful way to restrict sensitive capabilities on the system while being quite straight forward to use.

Case Study: fuchsia.identity.credential.Manager

Let's take a quick look at an existing restricted protocol fuchsia.identity.credential.Manager.

This is the entry in the policy file that restricts this component to only be used by the password_authenticator.

{
    source_moniker: "/core/account/credential_manager",
    source: "component",
    source_name: "fuchsia.identity.credential.Manager",
    capability: "protocol",
    target_monikers: [
        "/core/account/credential_manager",
        "/core/account/password_authenticator",
    ],
},

1. source_moniker: Identify where the component is exposed from; in this case that's, /core/account/credential_manager.
2. source: This is generally just component if you are serving your protocol from that component. It may be that you are working on the component_manager itself in which case you may need the framework capability.
3. capability: Identify the capability type. In this case this is just a protocol but you can also restrict other things like directory or an event. Most of the time it will be a protocol if it is an API that you are restricting.
4. Test it: I suggest leaving the target_moniker blank and running the CL in CQ at this point. This should break if anything is using your capability. If nothing breaks you probably have a typo.
5. target_monikers: In this case the protocol is only being routed to the password_authenticator and so we just provide that one route. Currently there is a bug where we also have to provided the source_moniker in the set of target monikers. This documentation will be updated when that is no longer a requirement.
6. Upload your CL and check it in!