Honneywell multics? from panels. the inline phots in this message folks -smecc

Noel Chiappa jnc at mercury.lcs.mit.edu
Thu Mar 17 08:03:27 CDT 2016

    > From: Mouse

    > As for buffer overruns, the point there is that a buffer overrun
    > clobbers memory addressed higher than the buffer. If the stack grows
    > down, this can overwrite stack frames and/or callers' locals.

Oh, right. Duhhhh! Buffers typically grow upward, no matter which direction
the stack grows. So the two directions for stack growth aren't purely a

Of course, in Multics, especially with AIM (Access Isolation Mechanism),
stack buffer attacks are much less dangerous. E.g. even without AIM, the
attacker can't load code into the stack, and return to it - generally the
stack segment had execute permission turned off.

And AIM really limits what 'bad' code can get up to. I keep ranting about
it's pointless to expect programmers to write code without security flaws, it
needs to be built in to the low levels of the system (one of Multics' many
lessons - it wasn't _really_ secure until the 6180 moved the ring stuff into
hardware, instead of simulating it in software, as on the 645). And so as
long as we continue to allow Web pages to contain 'active' content (i.e.
code), so that random code from all over the planet gets loaded into our
computers and run, browsers will neve be secure; they need to be run in an
AIM box.


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