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    SubjectRe: [PATCH v3 5/6] x86/ftrace: Use text_poke()
    [ live-patching ML CCed ]

    On Tue, 15 Oct 2019, Peter Zijlstra wrote:

    > On Tue, Oct 15, 2019 at 03:07:40PM +0200, Jessica Yu wrote:
    >
    > > > The fact that it is executable; also the fact that you do it right after
    > > > we mark it ro. Flipping the memory protections back and forth is just
    > > > really poor everything.
    > > >
    > > > Once this ftrace thing is sorted, we'll change x86 to _refuse_ to make
    > > > executable (kernel) memory writable.
    > >
    > > Not sure if relevant, but just thought I'd clarify: IIRC,
    > > klp_module_coming() is not poking the coming module, but it calls
    > > module_enable_ro() on itself (the livepatch module) so it can apply
    > > relocations and such on the new code, which lives inside the livepatch
    > > module, and it needs to possibly do this numerous times over the
    > > lifetime of the patch module for any coming module it is responsible
    > > for patching (i.e., call module_enable_ro() on the patch module, not
    > > necessarily the coming module). So I am not be sure why
    > > klp_module_coming() should be moved before complete_formation(). I
    > > hope I'm remembering the details correctly, livepatch folks feel free
    > > to chime in if I'm incorrect here.
    >
    > You mean it does module_disable_ro() ? That would be broken and it needs
    > to be fixed. Can some livepatch person explain what it does and why?

    Yes, it does. klp_module_coming() calls module_disable_ro() on all
    patching modules which patch the coming module in order to call
    apply_relocate_add(). New (patching) code for a module can be relocated
    only when the relevant module is loaded.

    Miroslav

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