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    SubjectRe: [PATCH v3 5/6] x86/ftrace: Use text_poke()
    On Fri, 11 Oct 2019 14:59:03 +0200
    Peter Zijlstra <peterz@infradead.org> wrote:

    > On Thu, Oct 10, 2019 at 07:28:19PM +0200, Peter Zijlstra wrote:
    >
    > > Really the best solution is to move all the poking into
    > > ftrace_module_init(), before we mark it RO+X. That's what I'm going to
    > > do for jump_label and static_call as well, I just need to add that extra
    > > notifier callback.
    >
    > OK, so I started writing that patch... or rather, I wrote the patch and
    > started on the Changelog when I ran into trouble describing why we need
    > it.
    >
    > That is, I'm struggling to explain why we cannot flip
    > prepare_coming_module() and complete_formation().
    >
    > Yes, it breaks ftrace, but I'm thinking that is all it breaks. So let me
    > see if we can cure that.

    You are mainly worried about making text that is executable into
    read-write again. What if we kept my one patch that just changed the
    module in ftrace_module_enable() from read-only to read-write, but
    before we ever set it executable.

    Jessica, would this patch break anything?

    It moves the setting of the module execution to after calling both
    ftrace_module_enable() and klp_module_coming().

    This would make it possible to do the module code and still keep with
    the no executable code becoming writable.

    -- Steve

    diff --git a/kernel/module.c b/kernel/module.c
    index ff2d7359a418..6e2fd40a6ed9 100644
    --- a/kernel/module.c
    +++ b/kernel/module.c
    @@ -3728,7 +3728,6 @@ static int complete_formation(struct module *mod, struct load_info *info)

    module_enable_ro(mod, false);
    module_enable_nx(mod);
    - module_enable_x(mod);

    /* Mark state as coming so strong_try_module_get() ignores us,
    * but kallsyms etc. can see us. */
    @@ -3751,6 +3750,11 @@ static int prepare_coming_module(struct module *mod)
    if (err)
    return err;

    + /* Make module executable after ftrace is enabled */
    + mutex_lock(&module_mutex);
    + module_enable_x(mod);
    + mutex_unlock(&module_mutex);
    +
    blocking_notifier_call_chain(&module_notify_list,
    MODULE_STATE_COMING, mod);
    return 0;
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