Patent ID: 11023237

Abstract:
An apparatus and method are provided for interpreting permissions associated with a capability. The apparatus has processing circuitry for executing instructions in order to perform operations, and a capability storage element accessible to the processing circuitry and arranged to store a capability used to constrain at least one operation performed by the processing circuitry when executing the instructions. The capability identifies a plurality N of default permissions whose state, in accordance with a default interpretation, is determined from N permission flags provided in the capability. In accordance with the default interpretation, each permission flag is associated with one of the default permissions. The processing circuitry is then arranged to analyse the capability in accordance with an alternative interpretation, in order to derive, from logical combinations of the N permission flags, state for an enlarged set of permissions, where the enlarged set comprises at least N+1 permissions. This provides a mechanism for encoding additional permissions into capabilities without increasing the number of permission flags required, whilst still retaining desirable behaviour.