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Message-ID: <1465869698.18900.2.camel@ellerman.id.au>
Date: Tue, 14 Jun 2016 12:01:38 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Kees Cook <keescook@...omium.org>, "Austin S. Hemmelgarn"
<ahferroin7@...il.com>
Cc: Emese Revfy <re.emese@...il.com>, Paul Gortmaker
<paul.gortmaker@...driver.com>, Michal Marek <mmarek@...e.com>, Stephen
Rothwell <sfr@...b.auug.org.au>, Sudip Mukherjee
<sudipm.mukherjee@...il.com>, Linux-Next <linux-next@...r.kernel.org>, LKML
<linux-kernel@...r.kernel.org>, "kernel-hardening@...ts.openwall.com"
<kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH] gcc-plugins: disable under COMPILE_TEST
On Mon, 2016-06-13 at 13:11 -0700, Kees Cook wrote:
> On Mon, Jun 13, 2016 at 11:32 AM, Austin S. Hemmelgarn
> <ahferroin7@...il.com> wrote:
> > On 2016-06-12 20:18, Emese Revfy wrote:
> > >
> > > On Sun, 12 Jun 2016 15:25:39 -0700
> > > Kees Cook <keescook@...omium.org> wrote:
> > >
> > > > I don't like this because it means if someone specifically selects
> > > > some plugins in their .config, and the headers are missing, the kernel
> > > > will successfully compile. For many plugins, this results in a kernel
> > > > that lacks the requested security features, and that I really do not
> > > > want to have happening. I'm okay leaving these disabled for compile
> > > > tests for now. We can revisit this once more distros have plugins
> > > > enabled by default.
> > >
> > > You are right. Your patch is safer.
> > >
> > Why not make it so that if COMPILE_TEST is enabled, the build warns if it
> > can't find the headers, otherwise it fails? That way, people who are doing
> > all*config builds but don't have the headers will still get some build
> > coverage, and the people who are enabling it as a security feature will
> > still get build failures.
>
> I don't see a clear way to do this, but if you can find a way to make
> that happen, please send a patch! :)
Another option is to make the top-level option negative, that way when it's
enabled by allmod/yes the plugins are turned off.
So eg. you would have:
config DISABLE_GCC_PLUGINS
bool "Disable building GCC plugins"
default y
...
This makes all the problems with allmod/yes go away, and means you always honor
the users intent - when DISABLE_GCC_PLUGINS=n you can fail the build if you
can't build the plugins.
The downside is the logic's a bit awkward, ie. to enable the plugins you have to
disable the option which disables them.
cheers
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