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

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Date:   Sat, 6 Mar 2021 01:03:32 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-hardening@...r.kernel.org,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Justin Forbes <jforbes@...hat.com>,
        Ondrej Mosnacek <omosnace@...hat.com>,
        Frank Eigler <fche@...hat.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH RFC] gcc-plugins: Handle GCC version mismatch for OOT modules

On Fri, Mar 5, 2021 at 11:41 AM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> On Thu, Mar 04, 2021 at 11:12:42AM -0800, Linus Torvalds wrote:
> > On Thu, Mar 4, 2021 at 7:36 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
> > >
> > > All the kernel-space objects are rebuilt
> > > when the compiler is upgraded.
> >
> > I very much NAK'ed that one. Why did that go in?
> >
> > Or maybe I NAK'ed another version of it (I think the one I NAK'ed was
> > from Josh), and didn't realize that there were multiple ones.
>
> This thread is making me dizzy,

Me too.

> Ok.  So it sounds like the best/easiest option is the original patch in
> this thread:  when building an external module with a GCC mismatch, just
> disable the GCC plugin, with a warning (or an error for randstruct).

Just for clarification,
I believe "the original patch" pointed to this one:
https://lore.kernel.org/lkml/efe6b039a544da8215d5e54aa7c4b6d1986fc2b0.1611607264.git.jpoimboe@redhat.com/

This is dead. Please do not come back to this.
See negative comments not only from me,
but also from Greg, Peter, Christoph.



> but I think the patch you NAK'ed from me
> was different.  It just added an error on GCC mismatch with external
> modules:
>
>   https://lkml.kernel.org/r/fff056a7c9e6050c2d60910f70b6d99602f3bec4.1611863075.git.jpoimboe@redhat.com
>
> though I think you were ok with downgrading it to a warning.

I think this was not NAKed.

At first, Linus NAKed it, but I think it was
just because of some misunderstanding.

I do not have an objection about checking
compiler version difference for external module
builds.

I was pointing out some mistakes in the Makefile implementation.
(I would say "not that way" even with your second trial).


--
Best Regards
Masahiro Yamada