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Date: Thu, 6 Dec 2018 10:25:17 -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 v2 1/1] stackleak: Register the 'stackleak_cleanup' pass
 before the '*free_cfg' pass

On Thu, Dec 6, 2018 at 7:13 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 '*free_cfg' pass. It's the moment when the stack frame size is
> already final, function prologues and epilogues are generated, and the
> machine-dependent code transformations are not done.
>
> [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! I've applied this to me tree and I'll send a pull request soon.

-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..dbd3746 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 "*free_cfg"
> +        * pass. It's the moment when the stack frame size is already final,
> +        * function prologues and epilogues are generated, and the
> +        * machine-dependent code transformations are not done.
>          */
> -       PASS_INFO(stackleak_cleanup, "reload", 1, PASS_POS_INSERT_AFTER);
> +       PASS_INFO(stackleak_cleanup, "*free_cfg", 1, PASS_POS_INSERT_BEFORE);
>
>         if (!plugin_default_version_check(version, &gcc_version)) {
>                 error(G_("incompatible gcc/plugin versions"));
> --
> 2.7.4
>


-- 
Kees Cook

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