IBM Mainframe Discussion List <IBM-MAIN@BAMA.UA.EDU> wrote on 11/08/2007 08:21:55 PM:
> >Otherwise, as I recall [MVS environments], that page is Key0 > non-fetch protected. > > Not true any more. The upper half of virtual page 0 (aka PSA) is fetch > protected by yet another different, independent protection > mechanism. This is so > that non-key 0 programs cannot look at the upper half of page 0, in which > many register save areas are defined in the z/OS PSA DSECT. There might be > clear text, passwords, or who knows what in a register that would > be visible to > an unauthorized program if such save areas were not fetch-protected somehow. > The lower half of page 0 is in key 0 and not fetch protected. Actually, a PSA frame in MVS is key 0 and fetch protected. MVS sets the Fetch-protection-override Control bit in control register 0 to allow the lower half (offset 0:x'7FF') to be fetched by a non-key 0 program. Jim Mulder z/OS System Test IBM Corp. Poughkeepsie, NY ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
