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    SubjectRe: Mprotect needs arch hook for updated PTE settings
    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/* changing the protection of the text
    segment of the _victim_ application, when it linked the library references.* changes the protection for the whole text segment
    (otherwise, as the protection is per VMA, it would result in a VMA
    The text segment can be huge. There is no reason to flush all the text
    segment every time when* 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.


    Zoltan Menyhart
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