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From:   Kees Cook <keescook@chromium.org>
Date:   Fri, 30 Nov 2018 09:09:02 -0800
Message-ID: <CAGXu5jJ7LmHRJJxtH2HD4XEu5hPLtAe=koJbaCmqF9qoSw=sVw@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 5:20 AM Alexander Popov <alex.popov@linux.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@intel.com>
> Signed-off-by: Alexander Popov <alex.popov@linux.com>

Thanks, applied!

-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