Re: Compiler alternatives to no-exec (was Re: non exec

Rene Janssen (rjanssen@ns.oke.nl)
Fri, 07 Aug 1998 14:22:58 +0200

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At 06:20 AM 8/7/98 GMT, Linus Torvalds wrote:
>In article <y7rogtxzkdr.fsf@sytry.doc.ic.ac.uk>,
>
>Zero also happens to be very cheap to test against. Total overhead: four
>instructions per function
>
>+ pushl $0
> ...
>+ popl %ecx
>+ testl %ecx,%ecx
>+ jne abort
> ret
>

This is probably not sufficient for all cases. You have to put 2 zero
guard bytes around the return address to be more secure. Overwriting the
returnadress can be done from two directions in theory.

Cheers,

René

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