Messages in this thread | | | Subject | Re: Unexecutable stack | Date | Tue, 28 Dec 1999 16:46:05 +0000 (GMT) | From | Alan Cox <> |
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> Could the designer of the non-executable-stack code please explain how > this works on an ix86 machine? The ix86 can't differentiate > between read and execute in hardware. This means that either the > patch for ix86 is a no-op or, (I shudder), a trap is executed on > every user stack access, and the kernel code does a comparison.
Or the author is smart.. which is the case. The patch changes the ring 3 code segment descriptor to limit below the stack. Executing code on the stack traps via a trampoline detector. It works rather nicely considering the limits the CPU imposes.
On sane machines the kernel does not need to be involved - you can do non executable stack simply by fixing ld.so and glibc a little on many platforms
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