linux-kernel - Re: Designated initializers, struct randomization and addressing?

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Message-ID: <alpine.DEB.2.20.1701040726310.2004@hadrien>
Date:   Wed, 4 Jan 2017 07:27:03 +0100 (CET)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Kees Cook <keescook@...omium.org>
cc:     Joe Perches <joe@...ches.com>, LKML <linux-kernel@...r.kernel.org>,
        Dan Carpenter <error27@...il.com>,
        Oleg Drokin <oleg.drokin@...el.com>,
        Andreas Dilger <andreas.dilger@...el.com>,
        James Simmons <jsimmons@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "John L. Hammond" <john.hammond@...el.com>,
        Emoly Liu <emoly.liu@...el.com>,
        Vitaly Fertman <vitaly_fertman@...atex.com>,
        Bruno Faccini <bruno.faccini@...el.com>,
        Bruce Korb <bruce.korb@...il.com>, devel@...verdev.osuosl.org
Subject: Re: Designated initializers, struct randomization and addressing?



On Tue, 3 Jan 2017, Kees Cook wrote:

> On Tue, Dec 20, 2016 at 9:29 AM, Joe Perches <joe@...ches.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