linux-kernel - Re: [PATCH v3 5/6] x86/ftrace: Use text

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Message-ID: <20191016092304.GL2294@hirez.programming.kicks-ass.net>
Date:   Wed, 16 Oct 2019 11:23:04 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     Joe Lawrence <joe.lawrence@...hat.com>,
        Jessica Yu <jeyu@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, mhiramat@...nel.org,
        bristot@...hat.com, jbaron@...mai.com,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        mingo@...nel.org, namit@...are.com, hpa@...or.com, luto@...nel.org,
        ard.biesheuvel@...aro.org, jpoimboe@...hat.com,
        live-patching@...r.kernel.org
Subject: Re: [PATCH v3 5/6] x86/ftrace: Use text_poke()

On Wed, Oct 16, 2019 at 08:51:27AM +0200, Miroslav Benes wrote:
> On Tue, 15 Oct 2019, Joe Lawrence wrote:
> 
> > On 10/15/19 10:13 AM, Miroslav Benes wrote:
> > > 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.
> > 
> > FWIW, would the LPC blue-sky2 model (ie, Steve's suggestion @ plumber's where
> > livepatches only patch a single object and updates are kept on disk to handle
> > coming module updates as they are loaded) eliminate those outstanding
> > relocations and the need to perform this late permission flipping?
> 
> Yes, it should, but we don't have to wait for it. PeterZ proposed a 
> different solution to this specific issue in 
> https://lore.kernel.org/lkml/20191015141111.GP2359@hirez.programming.kicks-ass.net/
> 
> It should not be a problem to create a live patch module like that and the 
> code in kernel/livepatch/ is almost ready. Something like 
> module_section_disable_ro(mod, section) (and similar for X protection) 
> should be enough. Module reloads would still require juggling with the 
> protections, but I think it is all feasible.

Just had a browse around the module code, and while the section info is
in load_info, it doesn't get retained for active modules.

So I suppose I'll go add that for KLP enabled things.