linux-kernel - Re: [PATCH v4 15/16] module: Move where we mark modules RO,X

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Date:   Fri, 25 Oct 2019 11:16:34 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, rostedt@...dmis.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, jeyu@...nel.org,
        live-patching@...r.kernel.org
Subject: Re: [PATCH v4 15/16] module: Move where we mark modules RO,X

On Fri, Oct 25, 2019 at 08:44:56AM +0200, Petr Mladek wrote:
> On Thu 2019-10-24 15:16:34, Peter Zijlstra wrote:

> > Right, that really should be able to run early. Esp. after commit
> > 
> >   11e86dc7f274 ("x86/paravirt: Detect over-sized patching bugs in paravirt_patch_call()")
> > 
> > paravirt patching is unconditional. We _never_ run with the indirect
> > call except very early boot, but modules should have them patched way
> > before their init section runs.
> > 
> > We rely on this for spectre-v2 and friends.
> 
> Livepatching has the same requirement. The module code has to be fully
> livepatched before the module gets actually used.

Right, and that is just saying that all paravirt RELAs (pv_ops) can
basically be deleted from modules.

Which avoids the reported problem in yet another way.

> It means before mod->init() is called and before the module is moved
> into MODULE_STATE_LIVE state.

Funny thing, currently ftrace is running code before all that. It runs
code before klp_module_coming(), before jump_label patching.

My other patch in this thread fixes that.