Messages in this thread | | | Date | Wed, 16 Mar 2005 13:58:04 +0100 | From | Zoltan Menyhart <> | Subject | Re: Mprotect needs arch hook for updated PTE settings |
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An application should not change the protection of its _own_ text region without knowing well the requirements of the given architecture. I do not think we should add anything into the kernel for this case.
I did see /lib/ld-linux-ia64.so.* changing the protection of the text segment of the _victim_ application, when it linked the library references. ld-linux-ia64.so.* changes the protection for the whole text segment (otherwise, as the protection is per VMA, it would result in a VMA fragmentation). The text segment can be huge. There is no reason to flush all the text segment every time when ld-linux-ia64.so.* patches an instruction and changes the protection.
I think the solution should consist of these two measures:
1. Let's say that if an VMA is "executable", then it remains "executable" for ever, i.e. the mprotect() keeps the PROT_EXEC bit. As a result, if a page is faulted in for this VMA in the mean time, the old good mechanism makes sure that the I-caches are flushed.
2. Let's modify ld-linux-<arch>.so.*: having patched an instruction, it should take the appropriate, architecture dependent measure, e.g. for ia64, it should issue an "fc" instruction.
(Who cares for a debugger ? It should know what it does ;-).)
I think there is no need for any extra flushes.
Thanks,
Zoltan Menyhart - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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