linux-hardening - Re: [PATCH RFC] kbuild: Prevent compiler mismatch with external modules

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Message-ID: <CAHk-=wgh4DaZvTcFfBcDMKc1QXkKjwny_Z0H5JfzdwMTNTBkSw@mail.gmail.com>
Date:   Thu, 28 Jan 2021 13:03:15 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        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>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Miroslav Benes <mbenes@...e.cz>,
        David Laight <David.Laight@...lab.com>,
        Jessica Yu <jeyu@...nel.org>
Subject: Re: [PATCH RFC] kbuild: Prevent compiler mismatch with external modules

On Thu, Jan 28, 2021 at 12:52 PM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> Huh?  Why would you do a "make oldconfig" on a distro-released kernel
> before building an OOT module?

I guarantee you that this patch will *make* people do that.

> Hm?  Are you saying the check is too strict, since GCC9 binaries _might_
> be compatible with GCC10?

I'm saying that your argument about minor and major versions is bogus.

There is absolutely nothing that makes gcc9 object files not
compatible with gcc10.

And this is not just some theoretical issue: this is a fundamental
fact of EVERY SINGLE LIBRARY OUT THERE.

Do you think that when you compile your binaries with gcc-10, you need
to link against a standard library that has been compiled with gcc-10?

I really think the whole compiler version check is purely voodoo programming.

                 Linus