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Assert apps can access only approved HwBinder services
App domains which host arbitrary code must not have access to arbitrary HwBinder services. Such access unnecessarily increases the attack surface. The reason is twofold: 1. HwBinder servers do not perform client authentication because HIDL currently does not expose caller UID information and, even if it did, many HwBinder services either operate at a layer below that of apps (e.g., HALs) or must not rely on app identity for authorization. Thus, to be safe, the default assumption is that a HwBinder service treats all its clients as equally authorized to perform operations offered by the service. 2. HAL servers (a subset of HwBinder services) contain code with higher incidence rate of security issues than system/core components and have access to lower layes of the stack (all the way down to hardware) thus increasing opportunities for bypassing the Android security model. HwBinder services offered by core components (as opposed to vendor components) are considered safer because of point #2 above. Always same-process aka always-passthrough HwBinder services are considered safe for access by these apps. This is because these HALs by definition do not offer any additional access beyond what its client already as, because these services run in the process of the client. This commit thus introduces these two categories of HwBinder services in neverallow rules. Test: mmm system/sepolicy -- this does not change on-device policy Bug: 34454312 Change-Id: I4f5f4dd10b3fc3bb9d262dda532d4a23dcdf061d
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