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Date:   Wed, 16 Oct 2019 11:23:04 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Miroslav Benes <mbenes@suse.cz>
Cc:     Joe Lawrence <joe.lawrence@redhat.com>,
        Jessica Yu <jeyu@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>, x86@kernel.org,
        linux-kernel@vger.kernel.org, mhiramat@kernel.org,
        bristot@redhat.com, jbaron@akamai.com,
        torvalds@linux-foundation.org, tglx@linutronix.de,
        mingo@kernel.org, namit@vmware.com, hpa@zytor.com, luto@kernel.org,
        ard.biesheuvel@linaro.org, jpoimboe@redhat.com,
        live-patching@vger.kernel.org
Subject: Re: [PATCH v3 5/6] x86/ftrace: Use text_poke()
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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.