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Re: [PEN-TEST] Crusoe chip. (fwd)
From: "Shetron, Richard" <multics () ruserved com>
Date: Wed, 8 Nov 2000 08:18:14 -0500

You might want to look at some of the Multics information at
www.multicians.org regarding security.  IIRC out of the box, Multics
installs at a B2 security level.  Multics had read, execute, write
protection flags on all segments enforced by hardware and used by
software.  Stacks/heaps were alwasy read/write, programs were always
read/execute.

There was also a ring protection as well.  Instead of just user/superviser
modes there were 4 superviser modes and 4 user modes.  A lower security
mode was not allowed to change or access a higher security mode segment
depending on the 'ring brackets'.

From the Multics standpoint, this discussion on stack/heap protection
is late 60's technology and has been in standard use for over 30 years.

Forwarded message:

As Craig said, the good folks on Bugtraq have demonstrated that
preventing execution in the stack doesn't actually add important
protection, it just changes the way you have to mount your attack.

Furthermore, it would break various techniques that various language
implementations use, that legitimately require executing in the
stack. Some compilers like to generate code that installs trampoline
instructions into the stack (I believe this is mostly to help ease
interfacing between wildly different calling conventions); some
compile-n-go implementations might want to execute out of stack
storage.

If there were a real and important security benefit to a non-exec
stack, then the potential compatibility problems could be lived
with, as each could be fixed if the implementor chose. But they
point up a potential cost, and as the only benefit to a non-exec
stack is effectively security through obscurity --- if the attacker
knows you're doing it they can dodge --- it just doesn't seem worth
implementing. Of course the benefit would be greatest if you did a
private, one-off implementation. But implementation costs, and costs
of dealing with any resulting compatibility problems, are the
highest --- because they're not shared --- for such one-offs.

-Bennett


--
Richard Shetron  multics () ruserved com multics () acm rpi edu  NO UCE
What is the Meaning of Life?      There is no meaning,
It's just a consequence of complex carbon based chemistry; don't worry about it
The Super 76, "Free Aspirin and Tender Sympathy", Las Vegas Strip.


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