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    SubjectRe: [Security] proactive defense: using read-only memory, RO/NX modules

    * Kees Cook <> wrote:

    > Hi,
    > On Mon, Nov 08, 2010 at 07:13:24AM +0100, Ingo Molnar wrote:
    > > * Kees Cook <> wrote:
    > > > While Dan Rosenberg is working to make things harder to locate potential targets
    > > > in the kernel through fixing kernel address leaks[1], I'd like to approach a
    > > > related proactive security measure: enforcing read-only memory for things that
    > > > would make good targets.
    > >
    > > Nice! IMHO we need more of that. (If the readonly section gets big enough in
    > > practice we could perhaps even mark it large-page in the future. It could serve as
    > > an allocator to module code as well - that would probably be a speedup even for
    > > modules.)
    > Well, I can try to extract and send what PaX does, but it seems relatively
    > incompatible with the existing system that uses set_kernel_text_rw() and
    > friends.
    > > > - Modules need to be correctly marked RO/NX. This patch exists[3], but is
    > > > not in mainline. It needs to be in mainline.
    > > [...]
    > > >
    > > > [3];a=commitdiff;h=65187d24fa3ef60f691f847c792e8eaca7e19251
    > >
    > > The reason the RO/NX patch from Siarhei Liakh is not upstream yet is rather mundane:
    > > it introduced regressions - it caused boot crashes on one of my testboxes.
    > >
    > > But there is no fundamental reason why it shouldnt be upstream. We can push it
    > > upstream if the crashes are resolved and if it gets an Ack from Rusty or Linus
    > > for the module bits.
    > Oh, well, yes, that's a good reason. :) Where was this covered? I'd like to help
    > get it reproduced and ironed out.

    Matthieu Castet seems to have dusted off those patches and submitted two of them in
    this mail:

    Subject: [RFC] reworked NX protection for kernel data

    Matthieu, are you still interested in this topic?

    The original, broken patches were these -tip commits:

    1e858c081af5: x86, mm: RO/NX protection for loadable kernel modules
    18c60ddc9eff: x86, mm: NX protection for kernel data
    c226a2feba21: x86, mm: Set first MB as RW+NX
    b29d530510d4: x86, mm: Correcting improper large page preservation

    I reported one of the crashes in:

    Subject: Re: [tip:x86/mm] x86, mm: Set first MB as RW+NX

    on lkml.



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