Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!bryce
From: bryce@cbmvax.commodore.com (Bryce Nesbitt)
Newsgroups: comp.sys.m68k
Subject: How best to subvert MMU write protection?
Message-ID: <10708@cbmvax.commodore.com>
Date: 8 Apr 90 11:07:36 GMT
Reply-To: bryce@commodore.COM (Bryce Nesbitt)
Distribution: comp
Organization: Commodore Technology, West Chester, PA
Lines: 27


:::Questions for any MMU hacks out there:::

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1> I'm using a page table that imposes the same severe write-protection on both
Supervisor and User mode access to a certain area of memory.  From time to
time the Supervisor must write a longword to this area of memory.  I'm
looking for a more efficient way to subvert the protection.

2> Suppose I wanted to subvert not only the WP, but use an unmapped physical
address.  How then?  (( I already tried MOVES with a function code of
$7 -- nice idea but no dice )).



This page table consists entirely of short format invalid descriptors and
early termination descriptors (I don't believe in actual page descriptors :-).
The solution must work on a 68020/68851 or 68030.   Compatibility with the
bargain-basement 68040 MMU would be nice.
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-- 
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{o O} .     Bryce Nesbitt, Commodore-Amiga, Inc.
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