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SubjectRe: 64bit port
David Miller wrote:
>
> From: hpa@transmeta.com (H. Peter Anvin)
> Date: 1 May 1999 10:29:25 GMT
>
> No good... it's trivial for the malicious user to bypass the
> simple-minded check. The general problem is uncomputable.
>
> If you mark read-only pages as clean after you scan them, and do
> checks on ITLB misses for pages which have been written to, plus add a
> special hook in the kernel for the dynamic linker to write instruction
> relocations efficiently in the face of this, I believe it can be done
> without too much of a performance hit for dynamic linking.
>

Actually; I believe if you use the state-flipping trick I mentioned
previously, you will have no performance issues, since the dynamic
linker will run with the pages in the writable state. Only when
execution starts will the code pages flip into the execute state.

The downside, of course, is that you don't get the error until at
runtime, but that's the normal behaviour for illegal instructions anyway
(SIGILL).

-hpa

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