Processing Metadata, Policies, and Composite Tags

A method includes receiving, for metadata processing, a current instruction with associated metadata tags. The metadata processing is performed in a metadata processing domain isolated from a code execution domain including the current instruction. Each respective associated metadata tag represents a respective policy of the composite policy. For each respective metadata tag, the method includes determining, in the metadata processing domain and in accordance with the metadata tag and the current instruction, whether a rule exists for the current instruction in a rules cache. The rules cache may include rules on metadata used by the metadata processing to define allowed instructions. The determination of whether a rule exists results in a respective output, which may include generating a new rule and inserting the new rule in the rules cache. Control Status Registers, and associated tags, may be used to accomplish the metadata processing.