NX technology follow-up.

R. Clayton (rclayton@monmouth.edu)
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After poking around a bit, I've found that NX technology is pretty much what I
suspected: a modification to the Intel page-table format to include an
No-eXecute (as opposed to an execute) bit. To maintain backwards compatibility
(the dead hand of the past) the NX bit defaults to 0, allowing execution.

If the CPU supports the NX bit (checking for it and trapping on violations),
then the OS can be patched to enable it.

See

  http://www.uwsg.iu.edu/hypermail/linux/kernel/0406.0/0497.html
  http://en.wikipedia.org/wiki/NX
  http://www.openbsd.org/33.html

for more details. The OpenBSD page describes an alternate way to protect
against stack smashing.

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