RESTRICTING MEMORY AREAS FOR AN INSTRUCTION READ IN DEPENDENCE UPON A HARDWARE MODE AND A SECURITY FLAG

摘要

An apparatus for processing data (2) includes a processor (8), a memory (6) and memory control circuitry (12). The processor (8) operates in a plurality of hardware modes including a privileged mode and a user mode. When operating in the privileged mode, the processor (8) is blocked by the memory control circuitry (12) from fetching instructions from memory address regions (34, 38, 42) within the memory (6) which are writeable within the user mode if a security flag within register (46) is set to indicate that this blocking mechanism is active.