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    SubjectRe: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap()
    On Fri, Apr 07, 2017 at 09:14:29AM -0700, Andy Lutomirski wrote:
    > I think we're approaching this all wrong, actually. The fact that x86
    > has this CR0.WP thing is arguably a historical accident, and the fact
    > that PaX uses it doesn't mean that PaX is doing it the best way for
    > upstream Linux.
    >
    > Why don't we start at the other end and do a generic non-arch-specific
    > implementation: set up an mm_struct that contains an RW alias of the
    > relevant parts of rodata and use use_mm to access it. (That is,
    > get_fs() to back up the old fs, set_fs(USER_DS),
    > use_mm(&rare_write_mm), do the write using copy_to_user, undo
    > everything.)

    FWIW, I completely agree with this approach.

    That's largely the approach arm64 would have to take regardless (as per
    Hoeun's patches), and having a consistent common implementation would be
    desireable.

    There are a couple of other complications to handle (e.g. a perf
    interrupt coming in and trying to read from the mapping), but I think we
    can handle that generically.

    Thanks,
    Mark.

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