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Re: 2nd Linux kernel patch to remove stack exec
From: linux () MAILHOST UNI-KOBLENZ DE (Systemkennung Linux)
Date: Mon, 14 Apr 1997 00:26:59 +0200


Hi,

It's not really a problem -- everything should run just fine with my patch.
However, the patch will not prevent buffer overflow exploits for those
programs that use trampolines.

This means that as long as libc5 is being used, most (if not all) privileged
processes will have stack execution permission disabled. :)

As for glibc, maybe it is time to change it not to use trampolines?

A patch which does this should now be in the glibc 2.1 development source.

Admited trampolines are a stupid idea because their performance sucks
on many architectures.

AFAIK, they will cause some overhead for maintaining L1 code and data caches
coherency, since the stack frame is usually in the data cache -- resulting in
bad performance.

We're talking about some hundred cycles or more ...

  Ralf



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