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Date: Fri, 30 Nov 2018 09:12:26 -0800
From: Kees Cook <keescook@...omium.org>
To: Alexander Popov <alex.popov@...ux.com>
Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>, Jann Horn <jannh@...gle.com>, 
	Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...en8.de>, Thomas Gleixner <tglx@...utronix.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Steven Rostedt <rostedt@...dmis.org>, 
	Peter Zijlstra <peterz@...radead.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Florian Weimer <fweimer@...hat.com>, Richard Sandiford <richard.sandiford@....com>, 
	Segher Boessenkool <segher@...nel.crashing.org>, amonakov@...ras.ru, 
	Tycho Andersen <tycho@...ho.ws>, Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>, 
	Emese Revfy <re.emese@...il.com>, Thomas Garnier <thgarnie@...gle.com>, Ingo Molnar <mingo@...nel.org>, 
	Will Deacon <will.deacon@....com>, Alexei Starovoitov <ast@...nel.org>, 
	Ard Biesheuvel <ard.biesheuvel@...aro.org>, "H. Peter Anvin" <hpa@...or.com>, 
	"David S. Miller" <davem@...emloft.net>, 
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, gcc@....gnu.org, 
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] stackleak: Register the 'stackleak_cleanup' pass
 before the 'mach' pass

On Fri, Nov 30, 2018 at 9:09 AM Kees Cook <keescook@...omium.org> wrote:
>
> On Fri, Nov 30, 2018 at 5:20 AM Alexander Popov <alex.popov@...ux.com> wrote:
> >
> > Currently the 'stackleak_cleanup' pass deleting a CALL insn is executed
> > after the 'reload' pass. That allows gcc to do some weird optimization in
> > function prologues and epilogues, which are generated later [1].
> >
> > Let's avoid that by registering the 'stackleak_cleanup' pass before
> > the 'mach' pass, which performs the machine dependent code transformations.
> > It's the moment when the stack frame size is final and function prologues
> > and epilogues are already generated.
> >
> > [1] https://www.openwall.com/lists/kernel-hardening/2018/11/23/2
> >
> > Reported-by: kbuild test robot <lkp@...el.com>
> > Signed-off-by: Alexander Popov <alex.popov@...ux.com>
>
> Thanks, applied!

Eek, no, this is breaking my build badly:

*** WARNING *** there are active plugins, do not report this as a bug
unless you can reproduce it without enabling any plugins.
Event                            | Plugins
PLUGIN_START_UNIT                | stackleak_plugin
kernel/exit.c: In function ‘release_task’:
kernel/exit.c:228:1: internal compiler error: Segmentation fault
 }

Failing with:

gcc (Ubuntu 7.3.0-16ubuntu3) 7.3.0

-Kees

>
> -Kees
>
> > ---
> >  scripts/gcc-plugins/stackleak_plugin.c | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/scripts/gcc-plugins/stackleak_plugin.c b/scripts/gcc-plugins/stackleak_plugin.c
> > index 2f48da9..6f41b32 100644
> > --- a/scripts/gcc-plugins/stackleak_plugin.c
> > +++ b/scripts/gcc-plugins/stackleak_plugin.c
> > @@ -363,10 +363,12 @@ __visible int plugin_init(struct plugin_name_args *plugin_info,
> >                                                 PASS_POS_INSERT_BEFORE);
> >
> >         /*
> > -        * The stackleak_cleanup pass should be executed after the
> > -        * "reload" pass, when the stack frame size is final.
> > +        * The stackleak_cleanup pass should be executed before the "mach"
> > +        * pass, which performs the machine dependent code transformations.
> > +        * It's the moment when the stack frame size is already final and
> > +        * function prologues and epilogues are generated.
> >          */
> > -       PASS_INFO(stackleak_cleanup, "reload", 1, PASS_POS_INSERT_AFTER);
> > +       PASS_INFO(stackleak_cleanup, "mach", 1, PASS_POS_INSERT_BEFORE);
> >
> >         if (!plugin_default_version_check(version, &gcc_version)) {
> >                 error(G_("incompatible gcc/plugin versions"));
> > --
> > 2.7.4
> >
>
>
> --
> Kees Cook



-- 
Kees Cook

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