linux-hardening - Re: [PATCH RFC] gcc-plugins: Handle GCC version mismatch for OOT modules

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Message-ID: <202101260955.F83D191B@keescook>
Date:   Tue, 26 Jan 2021 09:56:10 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-hardening@...r.kernel.org, linux-kbuild@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Justin Forbes <jforbes@...hat.com>,
        Ondrej Mosnacek <omosnace@...hat.com>
Subject: Re: [PATCH RFC] gcc-plugins: Handle GCC version mismatch for OOT
 modules

On Mon, Jan 25, 2021 at 04:19:53PM -0600, Josh Poimboeuf wrote:
> On Mon, Jan 25, 2021 at 02:03:07PM -0800, Kees Cook wrote:
> > On Mon, Jan 25, 2021 at 02:42:10PM -0600, Josh Poimboeuf wrote:
> > > When a GCC version mismatch is detected, print a warning and disable the
> > > plugin.  The only exception is the RANDSTRUCT plugin which needs all
> > > code to see the same struct layouts.  In that case print an error.
> > 
> > I prefer this patch as-is: only randstruct needs a hard failure. The
> > others likely work (in fact, randstruct likely works too).
> 
> I'm curious about this last statement, why would randstruct likely work?
> 
> Even struct module has '__randomize_layout', wouldn't basic module init
> go splat?

No; the seed is part of the generate includes -- you'll get the same
layout with the same seed.

-- 
Kees Cook