<snip>
We have a requirement to attach user modules from an unauthorised library
and execute them from an STC which runs APF authorised.
</snip>

You need to reject that requirement. It cannot be accomplished while 
maintaining system integrity. Use of something like "fork" can perhaps 
accomplish the goal without meeting the letter of the requirement.

<snip>
Well, if you want to run unauthorized stuff you would first need to set 
your
job as non-APF by resetting the bit.
</snip>

And if you do that, you must *never* turn the bit back on. Turning of 
JSCBAUTH is a fairly common approach, once the "authorized stuff" has been 
done. But you must then leave it off in order to maintain system 
integrity.

In all likelihood you should NEVER use RSAPF=YES. It is provided so that 
the initiator can attach the jobstep program task. I have no idea why it 
was documented. Way back when, even internal things were documented. Maybe 
when internal-only things were being removed from the books, no one 
realized how internal this one was.

The only z/OS-supported mechanism for authority-decreasing is SYNCH(X). 
And I do intentionally exclude authority-decreasing PC's (e.g., a PC that 
gets control in problem state when the invoker was supervisor state)  from 
what is supported by z/OS. You can't be stopped from doing so, but things 
likely won't behave the way you need if there was a (E)SPIE present. There 
might be cases other than (E)SPIE that similarly would cause anomalous 
behavior. I have no idea if this is documented explicitly. It's just 
something I remember being told long long ago.

Peter Relson
z/OS Core Technology Design


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