360 Assembly/Privileged Instructions

Privileged Instructions are programming instructions that need to be restrited to the operating system in order to protect system resources, system integrity, or system security. These include, but are not limited to:

• I/O instructions. To make sure two programs do not try to write to a printer, or edit a database record, or other errors that could corrupt files, a program issues I/O requests to the operating system, and it handles these operations.
• Load PSW. The PSW (program status word) con tains the status about the computer and the currently executing job. Without protecting the PSW, programs could
  • Grant themselves privileges
  • Allow themselves to reset their storage key, allowing them to change any memory
  • Rewrite, contaminate or destroy page tables, losing or corrupting other jobs
  • Change the system date and time
  • Halt the machine
• Insert storage key, set storage key. Change or read any memory.
• Page table functions. Contaminate other jobs, lose pages swapped out to disc, corrupt memory and/or other jobs.
• Diagnose. Used by operating systems to issue requests to the hypervisor.

It's probably best to restrict privileged functions to the operating system than allow just anyone to use them willy-nilly.