Re: [PATCH v3 5/6] x86/ftrace: Use text_poke()

[Jessica Yu]

+++ Steven Rostedt [15/10/19 09:28 -0400]:
> On Fri, 11 Oct 2019 14:59:03 +0200
> Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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;

As long as we enable x before parse_args(), which this patch does, then
I don't think this change would break anything.