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From:   Kees Cook <keescook@chromium.org>
Date:   Fri, 30 Nov 2018 09:12:26 -0800
Message-ID: <CAGXu5jKcRLcAg7r-E-9LMjK0YisLJp2TVYoiBwE+4ctYzi5wkg@mail.gmail.com>
Subject: Re: [PATCH 1/1] stackleak: Register the 'stackleak_cleanup' pass
 before the 'mach' pass
To:     Alexander Popov <alex.popov@linux.com>
Cc:     Kernel Hardening <kernel-hardening@lists.openwall.com>,
        Jann Horn <jannh@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Florian Weimer <fweimer@redhat.com>,
        Richard Sandiford <richard.sandiford@arm.com>,
        Segher Boessenkool <segher@kernel.crashing.org>,
        amonakov@ispras.ru, Tycho Andersen <tycho@tycho.ws>,
        Laura Abbott <labbott@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Emese Revfy <re.emese@gmail.com>,
        Thomas Garnier <thgarnie@google.com>,
        Ingo Molnar <mingo@kernel.org>,
        Will Deacon <will.deacon@arm.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "David S. Miller" <davem@davemloft.net>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        gcc@gcc.gnu.org, LKML <linux-kernel@vger.kernel.org>
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On Fri, Nov 30, 2018 at 9:09 AM Kees Cook <keescook@chromium.org> wrote:
>
> On Fri, Nov 30, 2018 at 5:20 AM Alexander Popov <alex.popov@linux.com> wr=
ote:
> >
> > 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 transformati=
ons.
> > It's the moment when the stack frame size is final and function prologu=
es
> > and epilogues are already generated.
> >
> > [1] https://www.openwall.com/lists/kernel-hardening/2018/11/23/2
> >
> > Reported-by: kbuild test robot <lkp@intel.com>
> > Signed-off-by: Alexander Popov <alex.popov@linux.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 =E2=80=98release_task=E2=80=99:
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-plugi=
ns/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 "ma=
ch"
> > +        * pass, which performs the machine dependent code transformati=
ons.
> > +        * It's the moment when the stack frame size is already final a=
nd
> > +        * 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


--=20
Kees Cook