Storage protection

CICS® uses the storage protection facilities that are available in the operating system to prevent CICS code and control blocks from being overwritten accidentally by your user application programs. To do this, separate dynamic storage areas (DSAs), with separate storage keys, are allocated for your user application programs, and for CICS code and control blocks. Access to a storage area is not permitted unless the access key matches the key for that storage area.

The storage allocated for most CICS code and control blocks is known as CICS-key storage, and the storage allocated for your user application programs is known as user-key storage.

In addition to CICS-key and user-key storage, CICS also uses key-0 storage for separate dynamic storage areas called the read-only DSAs (RDSA and ERDSA). The ERDSA is used for eligible re-entrant CICS and user application programs that are link-edited with the RENT and RMODE(ANY) attributes. The RDSA is used for eligible reentrant CICS and user application programs that are link-edited with the RENT and RMODE(24) attributes. The allocation of key-0 storage for the read-only DSAs is from the same storage limit as the other DSAs, as specified by the DSALIM and EDSALIM system initialization parameters.

Use of the storage protection facilities is optional. You can enable the facilities by using options on the system initialization parameters that are related to storage protection. Between them, you can use these parameters to define or control the following items:
  • The storage key for the common work area (CWAKEY)
  • The storage key for the terminal control table user areas (TCTUAKEY)
  • A storage protection global option (STGPROT)
  • A read-only program storage key option (RENTPGM)
  • A transaction isolation option (TRANISO)

Storage protection, transaction isolation, and command protection protect storage from user application code. They add no benefit to a region where no user code is executed; that is, a pure terminal-owning region (TOR) or a pure file-owning region (FOR) (where no distributed program link (DPL) requests are function-shipped).