A system is provided to perform secure operations. The system includes an I/O subsystem, a memory subsystem and processors. The processors are operative to execute processes in trusted execution environments (TEEs) and rich execution environments (REEs). Each of the TEEs and the REEs is identified by a corresponding access identifier (AID) and protected by a corresponding system resource protection unit (SRPU). The corresponding SRPU of a TEE includes instructions, when executed by a corresponding processor, cause the corresponding processor to control access to the TEE using a data structure including allowed AIDs and pointers to memory locations accessible by the allowed AIDs.