[Info-vax] How dangerous is it to be able to get into DCL supervisor mode ?

[VAXman- at SendSpamHere.ORG]

In article <ojg99i$vm8$2 at dont-email.me>, David Froble <davef at tsoft-inc.com> writes:
>VAXman- @SendSpamHere.ORG wrote:
>> In article <ojegsn$kf$1 at dont-email.me>, Simon Clubley <clubley at remove_me.eisner.decus.org-Earth.UFP> writes:
>>> On 2017-07-03, VAXman-  @SendSpamHere.ORG <VAXman- at SendSpamHere.ORG> wrote:
>>>> When in exec mode, one can invoke $CMKRNL and execute code in kernel
>>>> mode without possessing the privies needed for $CMKRNL because there
>>>> is a check for the previous mode being exec.  There's nothing similar
>>>> for $CMEXEC from supervisor mode.  It sure would have removed a few
>>>> hurdles for me when writing my DCL Debugger had that been the case.
>>>>
>>> Thanks Brian.
>>>
>>> There's still the bit about being able to set the privilege bits
>>> in supervisor mode however.
>>>
>>> However, if supervisor mode lets you do that, then that would seem to
>>> defeat the whole point of actually _having_ a supervisor mode. :-)
>> 
>> Because I'm already in supervisor mode with the debugger, I'll check on
>> this but I have some other issues that I need to focus on first.  Also,
>> it's US In-Dependence Day here.
>> 
>
>What do you do in the DCL debugger when the image is interrupted?  Such as 
>CTRL-Y?  I'm going to assume that you don't leave the process in supervisor mode?

*I* don't do anything!  DCL does it! ;)  The debugger is a tiny, relatively
speaking, piece of code that is actived by LOGINOUT.EXE instead of DCL.  It
then activates DCL with a simple intercept in one strategic location.  Save
for that, you have DCL running.  Whatever it does, it does; nothing changes
because of the debugger.  I took extreme precautions to INSURE that there's
no way to exploit my DCL debugger for nefarious malfeasance!



>Which causes me to be curious.  What happens after CTRL-Y and then "CONTINUE"?

The image, assuming it had no CTRL-Y handler if its own to invoke its rundown
or exit, will continue running where it was interrupted. 
-- 
VAXman- A Bored Certified VMS Kernel Mode Hacker    VAXman(at)TMESIS(dot)ORG

I speak to machines with the voice of humanity.