Rinat Sadretdinow wrote in a message to Detlef Engert:

 DE> Nothing in OS/2 stops you from entering 32-bit segments and retaining
 DE> IOPL privileges after you went through a 16-bit ring-2 callgate. The
 DE> only problem is to set up or find a proper ring-2 32-bit code
 DE> selector, but it's possible - rest assured.

 RS> Thank you for advice. I will try this as soon as possible.

Note that there is no way to make the necessary set up except from Ring 0,
in which case all of this is pointless.  Since OS/2 provides a facility for
loading a 16-bit segment with IOPL, and for calling into such a 16-bit
segment from a 32-bit segment, you should use the provided facilities.

It is possible to do all sorts of equally foolish things from Ring 0 code,
such as mapping a selector to run Ring 3 code at Ring 0 privilege, and I
have seen things like this done.  My opinion is that such a trick is an
example of programming incompetence, since it completely bypasses the
memory protection architecture of OS/2.  More to the point, it accomplishes
nothing that could not be done using a proper design.
 
-- Mike


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