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) contains the status about the computer and the currently executing job. 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. Programs that do not have privileges are known as "problem" programs. Without protecting the PSW, page tables, or I/O devices, problem 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 Anyone having heard about or seen the effects of malware or ransomware can understand the kind of damage a rogue privileged program do to a computer. Unless you have your own machine (like using the Hercules emulator on Linux, Mac, Raspberry Pi, or Windows, and don't care if something in the virtual environment is damaged), or you know exactly what you're doing, it's probably best to restrict privileged functions to the operating system than allow just anyone to use them willy-nilly. However, because sometimes problem programs in a production environment legitimately have a need to execute privileged instructions or access operating system tables or memory belonging to another process, many installations will install a "private" SVC routine ("private" in that is only set up on that machine, and is not part of the "stock" operating system supplied by the developer) and that SVC either grants privileged state to that process or changes an operating system table to grant the program additional privilege(s). Often the same SVC can be used to reset the request, revoking the privilege. These are the privileged instructions: Legend:         Available on all models unless indicated by (360 only) or (360 & 370 only)         Available on the 370, 390 and z/System         Available on the 390 and z/System         Available only on the z/System Using any of these in a problem (unprivileged) program will cause a protection exception. Using one of these instructions in a privileged program on the wrong class of machine will cause an operation exception. Opcode(Hex) Mnemonic Description 08 SSK Set Storage Key (360 only) 09 ISK Insert Storage Key (360 only) 82 LPSW Load Program Status Word 84 WRD Write Direct (360 only) 85 RDD Read Direct (360 Only) 9C SIO Start I/O (360 Only) 9D TIO Test I/O (360 Only) 9D01 CLRIO CLeaR I/O (370 only) 9E HIO Halt I/O (360 only} 9F TCH Test CHannel (360 & 370 only) B200 CONCS Connect Channel Set B201 DISCS DISconnect Channel Set B202 STIDP Store CPU ID B204 SCK Set Clock B206 SCKC Set Clock Comparator B207 STCKC Store Clock Comparator B208 SPT Set CPU Timer B209 STPT Store CPU Timer B20A SPKA Set PSW Key From Address B20B IPK Insert PSW Key B20D PTLB Purge TLB B210 SPX Set Prefix B211 STPX Store Prefix B212 STAP Store CPU Address B213 RRB Reset Reference Bit B221 IPTE Invalidate Page Table Entry B223 IVSK Insert Virtual Storage Key B224 IAC Insert Address Space Control B225 SSAR Set Secondary ASN B226 EPAR Extract Primary ASN B227 ESAR Extract Secondary ASN B228 PT Program Transfer B229 ISKE Insert Storage Key Extended B22A RRBE Reset Storage Key Extended B22B SSKE Set Storage Key Extended B22C TB Test Block B22E PGIN Page In B22F PGOUT Page Out B230 CSCH Clear SubCHannel B231 HSCH Halt SubCHannel B232 MSCH Modify SubCHannel B233 SSCH Start SubCHannel B234 STSCH Store SubCHannel B235 TSCH Test SubCHannel B236 TPI Test Pending Interruption B237 SAL Set Address Limit B238 RSCH Resume SubCHannel B239 STCRW Store Channel Report Word B23A STCPS Store Channel Path Status B23B RCHP Reset Channel Path B23C SCHM Set Channel Monitor B246 STURA STore Using Real Address B248 PALB Purge ALB B24B LURA Load Using Real Address B254 MVPG Move Page B277 RP Resume Program B2B1 STFL Store Facility List B2B2 LPSWE Load PSW Extended B6 STCTL Store ConTroL B7 LCTL Load ConTroL B905 LURAG Load Using Real Address (64 bit) B925 STURG Store Using Real Address B928 PCKMO Perform Cryptographic Key Mgmt Operations B98E IDTE Invalidate DAT Table Entry B98F CRDTE Compare and Replace DAT Table Entry B99A EPAIR Extract Primary ASN and Instance B99B ESAIR Extract Secondary ASN and Instance B99D ESEA Extract and Set Extended Authority B99E PTI Program Transfer with Instance B99F SSAIR Set Secondary ASN and Instance B9A1 TPEI Test Pending External Interruption B9A2 PTF Perform Topology Function B9AA LPTEA Load Page Table Entry Address B9AE RRBM Reset Reference Bits Multiple B9AF PFMF Perform Frame Management Function E500 LASP Load Address Space Parameters E501 TPROT Test PROTection E502 STRAG STore Real Address Grande EB0F TRACG TRACe Grande EB25 STCTG STore ConTrol (64) EB2F LCTLG Load Control (64)