From: Masahiro Yamada <masahiroy@kernel.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kees Cook <keescook@chromium.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Michal Marek <michal.lkml@markovi.net>,
linux-hardening@vger.kernel.org,
Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Justin Forbes <jforbes@redhat.com>,
Ondrej Mosnacek <omosnace@redhat.com>
Subject: Re: [PATCH RFC] gcc-plugins: Handle GCC version mismatch for OOT modules
Date: Tue, 26 Jan 2021 06:44:35 +0900 [thread overview]
Message-ID: <CAK7LNAS+EG9doX3qUmu4M3=mRNmdybSv4180Xnuubiwmsq0Agw@mail.gmail.com> (raw)
In-Reply-To: <20210125212755.jfwlqogpcarmxdgt@treble>
On Tue, Jan 26, 2021 at 6:28 AM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>
> On Tue, Jan 26, 2021 at 06:16:01AM +0900, Masahiro Yamada wrote:
> > On Tue, Jan 26, 2021 at 5:42 AM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > >
> > > When building out-of-tree kernel modules, the build system doesn't
> > > require the GCC version to match the version used to build the original
> > > kernel. That's probably [1] fine.
> > >
> > > In fact, for many distros, the version of GCC used to build the latest
> > > kernel doesn't necessarily match the latest released GCC, so a GCC
> > > mismatch turns out to be pretty common. And with CONFIG_MODVERSIONS
> > > it's probably more common.
> > >
> > > So a lot of users have come to rely on being able to use a different
> > > version of GCC when building OOT modules.
> > >
> > > But with GCC plugins enabled, that's no longer allowed:
> > >
> > > cc1: error: incompatible gcc/plugin versions
> > > cc1: error: failed to initialize plugin ./scripts/gcc-plugins/structleak_plugin.so
> > >
> > > That error comes from the plugin's call to
> > > plugin_default_version_check(), which strictly enforces the GCC version.
> > > The strict check makes sense, because there's nothing to prevent the GCC
> > > plugin ABI from changing -- and it often does.
> > >
> > > But failing the build isn't necessary. For most plugins, OOT modules
> > > will otherwise work just fine without the plugin instrumentation.
> > >
> > > 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.
> > >
> > > [1] Ignoring, for the moment, that the kernel now has
> > > toolchain-dependent kconfig options, which can silently disable
> > > features and cause havoc when compiler versions differ, or even when
> > > certain libraries are missing. This is a separate problem which
> > > also needs to be addressed.
> > >
> > > Reported-by: Ondrej Mosnacek <omosnace@redhat.com>
> > > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> > > ---
> >
> >
> > We are based on the assumption that we use the same
> > compiler for in-tree and out-of-tree.
>
> Sorry, but that assumption isn't based in reality. And it's not
> enforced.
>
> > If people use a different compiler, they must be
> > prepared for any possible problem.
> >
> > Using different compiler flags for in-tree and out-of-tree
> > is even more dangerous.
> >
> > For example, CONFIG_GCC_PLUGIN_RANDSTRUCT is enabled
> > for in-tree build, and then disabled for out-of-tree modules,
> > the struct layout will mismatch, won't it?
>
> If you read the patch you'll notice that it handles that case, when it's
> caused by GCC mismatch.
>
> However, as alluded to in the [1] footnote, it doesn't handle the case
> where the OOT build system doesn't have gcc-plugin-devel installed.
> Then CONFIG_GCC_PLUGIN_RANDSTRUCT gets silently disabled and the build
> succeeds! That happens even without a GCC mismatch.
Ah, sorry.
I responded too early before reading the patch fully.
But, I do not like to make RANDSTRUCT a special case.
I'd rather want to stop building for any plugin.
> > This patch is ugly, and not doing the right thing.
>
> Maybe, but I doubt the solution is to make assumptions.
>
> --
> Josh
>
--
Best Regards
Masahiro Yamada
next prev parent reply other threads:[~2021-01-25 21:48 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-25 20:42 [PATCH RFC] gcc-plugins: Handle GCC version mismatch for OOT modules Josh Poimboeuf
2021-01-25 21:16 ` Masahiro Yamada
2021-01-25 21:27 ` Josh Poimboeuf
2021-01-25 21:44 ` Masahiro Yamada [this message]
2021-01-25 22:07 ` Josh Poimboeuf
2021-01-26 8:13 ` Greg KH
2021-01-26 12:44 ` Justin Forbes
2021-01-26 13:51 ` Greg KH
2021-01-26 14:51 ` Josh Poimboeuf
2021-01-26 15:00 ` Greg KH
2021-01-26 15:15 ` Peter Zijlstra
2021-01-26 15:46 ` Josh Poimboeuf
2021-01-26 16:05 ` Peter Zijlstra
2021-01-26 16:15 ` Justin Forbes
2021-01-26 16:19 ` Josh Poimboeuf
2021-01-26 17:06 ` Greg KH
2021-01-26 17:47 ` Justin Forbes
2021-01-26 16:22 ` David Laight
2021-01-27 18:03 ` Christoph Hellwig
2021-01-26 8:12 ` Greg KH
2021-01-25 22:03 ` Kees Cook
2021-01-25 22:19 ` Josh Poimboeuf
2021-01-26 17:56 ` Kees Cook
2021-01-26 18:43 ` Josh Poimboeuf
2021-01-26 22:59 ` Kees Cook
2021-01-26 23:32 ` Josh Poimboeuf
2021-01-26 1:53 ` Masahiro Yamada
2021-01-26 12:16 ` David Laight
2021-01-27 18:02 ` Christoph Hellwig
2021-01-27 18:38 ` Josh Poimboeuf
2021-01-27 18:43 ` Christoph Hellwig
2021-01-27 18:51 ` Josh Poimboeuf
2021-01-27 22:09 ` David Laight
2021-01-28 14:29 ` Christoph Hellwig
2021-01-28 15:45 ` Josh Poimboeuf
2021-03-02 23:26 ` Josh Poimboeuf
2021-03-03 18:49 ` Masahiro Yamada
2021-03-03 19:15 ` Josh Poimboeuf
2021-03-03 19:25 ` Linus Torvalds
2021-03-03 19:38 ` Josh Poimboeuf
2021-03-03 19:57 ` Linus Torvalds
2021-03-03 20:24 ` Josh Poimboeuf
2021-03-03 20:31 ` Josh Poimboeuf
2021-03-03 20:56 ` Linus Torvalds
2021-03-03 21:45 ` Josh Poimboeuf
2021-03-04 12:27 ` Masahiro Yamada
2021-03-04 15:08 ` Josh Poimboeuf
2021-03-04 15:35 ` Masahiro Yamada
2021-03-04 19:12 ` Linus Torvalds
2021-03-05 2:41 ` Josh Poimboeuf
2021-03-05 2:49 ` Linus Torvalds
2021-03-05 16:03 ` Masahiro Yamada
2021-03-05 19:18 ` Josh Poimboeuf
2021-03-08 9:39 ` David Laight
2021-03-05 15:31 ` Masahiro Yamada
2021-03-03 21:52 ` Kees Cook
2021-03-04 12:26 ` Masahiro Yamada
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