Re: [PATCH 1/1] stackleak: Register the 'stackleak_cleanup' pass before the 'mach' pass

[Kees Cook]

On Fri, Nov 30, 2018 at 9:09 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> On Fri, Nov 30, 2018 at 5:20 AM Alexander Popov <alex.popov@xxxxxxxxx> 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@xxxxxxxxx>
> > Signed-off-by: Alexander Popov <alex.popov@xxxxxxxxx>
>
> 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 ârelease_taskâ:
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