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

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Message-ID: <CAGXu5j+DLRoVE88a9++jVfEkN90HDiAaDAMnT2TrKqtMZ_yOww@mail.gmail.com>
Date:	Wed, 27 Jan 2016 13:19:19 -0800
From:	Kees Cook <keescook@...omium.org>
To:	David Brown <david.brown@...aro.org>
Cc:	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Ingo Molnar <mingo@...hat.com>,
	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" <x86@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	PaX Team <pageexec@...email.hu>,
	Emese Revfy <re.emese@...il.com>,
	LKML <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 Wed, Jan 27, 2016 at 1:11 PM, David Brown <david.brown@...aro.org> wrote:
> 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;
>                    ^

Thanks! Yeah, I noticed this too when rebasing recently.

> 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.

I'm going to hope it's something easy like CONFIG_DEBUG_RODATA not being set. :)

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security