From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1762798AbcALQra (ORCPT <rfc822;w@1wt.eu>);
	Tue, 12 Jan 2016 11:47:30 -0500
Received: from mail.skyhub.de ([78.46.96.112]:42441 "EHLO mail.skyhub.de"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1759655AbcALQrZ (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Tue, 12 Jan 2016 11:47:25 -0500
Date: Tue, 12 Jan 2016 17:47:11 +0100
From: Borislav Petkov <bp@alien8.de>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, live-patching@vger.kernel.org,
        Michal Marek <mmarek@suse.cz>, Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andi Kleen <andi@firstfloor.org>, Pedro Alves <palves@redhat.com>,
        Namhyung Kim <namhyung@gmail.com>,
        Bernd Petrovitsch <bernd@petrovitsch.priv.at>,
        Chris J Arges <chris.j.arges@canonical.com>,
        Andrew Morton <akpm@linux-foundation.org>, Jiri Slaby <jslaby@suse.cz>,
        Arnaldo Carvalho de Melo <acme@kernel.org>
Subject: Re: [PATCH v15 13/25] x86/reboot: Add ljmp instructions to stacktool
 whitelist
Message-ID: <20160112164711.GD22699@pd.tnic>
References: <cover.1450442274.git.jpoimboe@redhat.com>
 <c0c1a92df921961cae5cce208247bb8d8a975d6d.1450442274.git.jpoimboe@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <c0c1a92df921961cae5cce208247bb8d8a975d6d.1450442274.git.jpoimboe@redhat.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, Dec 18, 2015 at 06:39:27AM -0600, Josh Poimboeuf wrote:
> stacktool reports a false positive warning for the ljmp instruction in
> machine_real_restart().  Normally, ljmp isn't allowed in a function, but
> this is a special case where it's jumping into real mode.
> 
> Add the jumps to a whitelist which tells stacktool to ignore them.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> ---
>  arch/x86/kernel/reboot.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
> index 02693dd..1ea1c5e 100644
> --- a/arch/x86/kernel/reboot.c
> +++ b/arch/x86/kernel/reboot.c
> @@ -9,6 +9,7 @@
>  #include <linux/sched.h>
>  #include <linux/tboot.h>
>  #include <linux/delay.h>
> +#include <linux/stacktool.h>
>  #include <acpi/reboot.h>
>  #include <asm/io.h>
>  #include <asm/apic.h>
> @@ -97,11 +98,13 @@ void __noreturn machine_real_restart(unsigned int type)
>  
>  	/* Jump to the identity-mapped low memory code */
>  #ifdef CONFIG_X86_32
> -	asm volatile("jmpl *%0" : :
> +	asm volatile(STACKTOOL_IGNORE_INSN
> +		     "jmpl *%0;" : :
>  		     "rm" (real_mode_header->machine_real_restart_asm),
>  		     "a" (type));
>  #else
> -	asm volatile("ljmpl *%0" : :
> +	asm volatile(STACKTOOL_IGNORE_INSN
> +		     "ljmpl *%0" : :
>  		     "m" (real_mode_header->machine_real_restart_asm),
>  		     "D" (type));
>  #endif

Well, I can't say that I'm crazy about all those new tools adding
markers to unrelated kernel code.

Can't you teach stacktool to ignore the whole machine_real_restart()
function simply?

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.