Re: Designated initializers, struct randomization and addressing?

From: Julia Lawall <julia.lawall@lip6.fr>
To: Kees Cook <keescook@chromium.org>
Cc: Joe Perches <joe@perches.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Dan Carpenter <error27@gmail.com>,
	Oleg Drokin <oleg.drokin@intel.com>,
	Andreas Dilger <andreas.dilger@intel.com>,
	James Simmons <jsimmons@infradead.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"John L. Hammond" <john.hammond@intel.com>,
	Emoly Liu <emoly.liu@intel.com>,
	Vitaly Fertman <vitaly_fertman@xyratex.com>,
	Bruno Faccini <bruno.faccini@intel.com>,
	Bruce Korb <bruce.korb@gmail.com>,
	devel@driverdev.osuosl.org
Subject: Re: Designated initializers, struct randomization and addressing?
Date: Wed, 4 Jan 2017 07:27:03 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.20.1701040726310.2004@hadrien> (raw)
In-Reply-To: <CAGXu5jJUHZi5LUxFjG9XfKgipBpGYfdfUXM8q_xEWqQrqtq1Tw@mail.gmail.com>

On Tue, 3 Jan 2017, Kees Cook wrote:

> On Tue, Dec 20, 2016 at 9:29 AM, Joe Perches <joe@perches.com> wrote:
> > On Fri, 2016-12-16 at 17:00 -0800, Kees Cook wrote:
> >> Prepare to mark sensitive kernel structures for randomization by making
> > sure they're using designated initializers.
> >
> > About the designated initializer patches,
> > which by themselves are fine of course,
> > and the fundamental randomization plugin,
> > c guarantees that struct member ordering
> > is as specified.
> >
> > how is the code to be verified so that
> > any use of things like offsetof and any
> > address/indexing is not impacted?
>
> AIUI, offsetof() works correctly in the face of this plugin, since the
> ordering happens before the pass that handles offsetof(). Anything
> that _does not_ use offsetof(), however, needs fixing. Based on the
> work done in grsecurity, I don't see any added offsetof() uses that
> are specific to the randomization plugin.
>
> (Note that the randomization plugin is only on function pointer
> structures, where using an offsetof() should be rare to none, and on
> hand-selected structures, where missing offsetof() should be easy to
> audit.)

What is the precise definition of "function pointer structures"?  Only
function pointers?  At least one function pointer?

thanks,
julia