Low Address Protection only applies to the first 512 bytes of PSA. An authorized program can alter the remaining 7/8 of this page without having to change a control register. There is also another protection applied to the upper half of PSA that requires key 0 to fetch the data. This prevents unauthorized users from looking at some control blocks in which registers are stored which could possibly not belong to the currently active program.
Bill Fairchild Franklin, TN ----- Original Message ----- From: "Steve Thompson" <sthomp...@us.ibm.com> To: IBM-MAIN@LISTSERV.UA.EDU Sent: Thursday, June 27, 2013 11:01:57 AM Subject: Re: z/OS subroutine in assembler, used in both batch & CICS , making r e-entrant From: Tom Marchant <m42tom-ibmm...@yahoo.com> Date: 06/27/2013 10:46 AM On Wed, 26 Jun 2013 22:45:50 -0700, Ed Jaffe wrote: >AFAIK, there is only one 4K range of virtual addresses guaranteed to >generate 0C4 now and forever: 7FFFF000 - 7FFFFFFF. I didn't know that. Is it documented anywhere? The 4K range from 00000000 - 00000FFF is key 0 storage and, as such, is protected from stores by unauthorized programs. -- Tom Marchant ------------------------------- Look in the z/Arch book (Principles) for LAP. It even prevents authorized programs from writing into the "PSA". [Low Address Protection ?] You have to set the LAP bit off in a CR to be able to update that area. Regards, Steve Thompson ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
