linux-kernel - Re: [kernel-hardening] [PATCH v4 3/8] param: convert some "on"/"off" users to strtobool

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Date:	Wed, 27 Jan 2016 14:11:05 -0700
From:	David Brown <david.brown@...aro.org>
To:	kernel-hardening@...ts.openwall.com
Cc:	Ingo Molnar <mingo@...hat.com>, Kees Cook <keescook@...omium.org>,
	Andy Lutomirski <luto@...capital.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Mathias Krause <minipli@...glemail.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Arnd Bergmann <arnd@...db.de>, PaX Team <pageexec@...email.hu>,
	Emese Revfy <re.emese@...il.com>, linux-kernel@...r.kernel.org,
	linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [kernel-hardening] [PATCH v4 3/8] param: convert some "on"/"off"
 users to strtobool

On Tue, Jan 19, 2016 at 10:08:37AM -0800, Kees Cook wrote:

>diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
>index 9cc20af58c76..f5ea98490ffa 100644
>--- a/kernel/time/tick-sched.c
>+++ b/kernel/time/tick-sched.c
>@@ -387,20 +388,14 @@ void __init tick_nohz_init(void)
> /*
>  * NO HZ enabled ?
>  */
>-static int tick_nohz_enabled __read_mostly  = 1;
>+static bool tick_nohz_enabled __read_mostly  = true;
> unsigned long tick_nohz_active  __read_mostly;
> /*
>  * Enable / Disable tickless mode
>  */

Just discovered this conflicts with a recent patch with
CONFIG_NO_HZ_COMMON:

	commit 46373a15f65fe862f31c19a484acdf551f2b442f
	Author: Jean Delvare <jdelvare@...e.de>
	Date:   Mon Jan 11 17:40:31 2016 +0100

	    time: nohz: Expose tick_nohz_enabled

kernel/time/tick-sched.c:390:6: error: conflicting types for ‘tick_nohz_enabled’
	bool tick_nohz_enabled __read_mostly = true;
	     ^
In file included from kernel/time/tick-internal.h:5:0,
                 from kernel/time/tick-sched.c:30:
include/linux/tick.h:101:12: note: previous declaration of ‘tick_nohz_enabled’ was here
	extern int tick_nohz_enabled;
	           ^

Fixing the compilation error, it compiles and boots on arm64, however
it isn't detecting the write (with the lkdtm test).  I'll continue
looking into what's preventing this.

David