linux-kernel - Re: [PATCH 3/3] powerpc: enable support for GCC plugins

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Message-ID: <CAGXu5jKrU5GR3KDb9M-vtSpY+aRm2B0vGpahVYLtFTWs=g7Big@mail.gmail.com>
Date:   Thu, 8 Dec 2016 10:06:55 -0800
From:   Kees Cook <keescook@...omium.org>
To:     PaX Team <pageexec@...email.hu>
Cc:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Emese Revfy <re.emese@...il.com>,
        Andrew Donnellan <andrew.donnellan@....ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        Brad Spengler <spender@...ecurity.net>,
        Michal Marek <mmarek@...e.com>
Subject: Re: [PATCH 3/3] powerpc: enable support for GCC plugins

On Thu, Dec 8, 2016 at 6:42 AM, PaX Team <pageexec@...email.hu> wrote:
> On 6 Dec 2016 at 17:28, Andrew Donnellan wrote:
>
>> Enable support for GCC plugins on powerpc.
>>
>> Add an additional version check in gcc-plugins-check to advise users to
>> upgrade to gcc 5.2+ on powerpc to avoid issues with header files (gcc <=
>> 4.6) or missing copies of rs6000-cpus.def (4.8 to 5.1 on 64-bit targets).
>
> i don't think that this is the right approach. there's a general and a special
> issue here, both of which need different handling.
>
> the general problem is to detect problems related to gcc plugin headers and
> notify the users about solutions. emitting various messages from a Makefile
> is certainly not a scalable approach, just imagine how it will look when the
> other 30+ archs begin to add their own special cases... if anything, they
> should be documented in Documentation/gcc-plugins.txt (or a new doc if it
> grows too big) and the Makefile message should just point at it.
>
> as for the solutions, the general advice should enable the use of otherwise
> failing gcc versions instead of forcing updating to new ones (though the
> latter is advisable for other reasons but not everyone's in the position to
> do so easily). in my experience all one needs to do is manually install the
> missing files from the gcc sources (ideally distros would take care of it).
>
> the specific problem addressed here can (and IMHO should) be solved in
> another way: remove the inclusion of the offending headers in gcc-common.h
> as neither tm.h nor c-common.h are needed by existing plugins. for background,
> i created gcc-common.h to simplify plugin development across all supportable
> gcc versions i came across over the years, so it follows the 'everything but
> the kitchen sink' approach. that isn't necessarily what the kernel and other
> projects need so they should just use my version as a basis and fork/simplify
> it (even i maintain private forks of the public version).

If removing those will lower the requirement for PPC, that would be
ideal. Otherwise, I'd like to take the practical approach of making
the plugins available on PPC right now, with an eye towards relaxing
the version requirement as people need it.

> as for the location of c-common.h, upstream gcc moved it under c-family in
> 2010 after the release of 4.5, so it should be where gcc-common.h expects
> it and i'm not sure how it ended up at its old location for you.

That is rather odd. What distro was the PPC test done on? (Or were
these manually built gcc versions?)

-Kees

-- 
Kees Cook
Nexus Security