In an embodiment, a data processing method comprises, in a computer executing a supervisor program: the supervisor program establishing a plurality of different memory access permissions comprising any combination of read, write, and execute permissions for one or more different regions of memory of a first domain; setting the memory access permissions of a first set of the regions of memory to execute only; in response to a request from a process to read or write a particular region of memory in the first set, performing one or more responsive actions that prevent the process from reading or modifying one or more instructions or one or more embedded immediate values of the particular region of memory. Embodiments provide selective access to executable memory.