Crash a RISC machine from user-mode code:

[Anton Rang]

[ This isn't really a C issue; I'm redirecting it to comp.misc. ]

In article <49041 at seismo.CSS.GOV> stead at beno.CSS.GOV (Richard Stead) writes:
>Do VAX-CISC programmers spend their days branching to random data?

  Nobody that I know of actually does this on *purpose*.  However,
it's not that hard to screw up a program so that it does this.  For
instance, passing the wrong argument (or an uninitialized pointer) to
a routine expecting a function pointer can do it.  Or trashing the
stack by going past array bounds.  Lots of possibilities.

>Or if I ever do, I would fix it pretty damn quick.

  Same here.  Nobody's saying that branching to random data is good.

>Who could possibly care that a random instruction sequence crashes a risc box?

  Well...if I have my own workstation, and always have all my work in
progress saved before I run a program (generally true for the most
part, since I'm paranoid) I don't care that much, though it's still
annoying .  If I'm sharing the machine, I *don't* want it to crash
twice a day because the guy down the hall is trying to find the
stack-clobbering bug in his code.

  Educational environments are even more prone to this.  If you have a
Sun-4/490 shared between 200 users, you don't want somebody to be able
to crash the machine at will ("denial of service" attack).  There are
students out there who will think this is a great joke....

  I hope that the problems shown up by this test can all be fixed in
software; I expect that they can, and that the vendors will do so.  In
general, nothing a user-mode process can do should be able to crash
the machine...otherwise, what's the point of privileged instructions,
kernel mode, etc.?

	Anton
   
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| Anton Rang (grad student) | rang at cs.wisc.edu | UW--Madison |
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