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 S1752235AbcDKICT (ORCPT <rfc822;w@1wt.eu>);
	Mon, 11 Apr 2016 04:02:19 -0400
Received: from foss.arm.com ([217.140.101.70]:47145 "EHLO foss.arm.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1750718AbcDKICR (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Mon, 11 Apr 2016 04:02:17 -0400
Message-ID: <570B59A5.3090904@arm.com>
Date: Mon, 11 Apr 2016 09:00:37 +0100
From: James Morse <james.morse@arm.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.6.0
MIME-Version: 1.0
To: Kees Cook <keescook@chromium.org>
CC: Linus Torvalds <torvalds@linux-foundation.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Matt Redfearn <matt.redfearn@imgtec.com>,
        Yves-Alexis Perez <corsac@debian.org>, Emrah Demir <ed@abdsec.com>,
        Jonathan Corbet <corbet@lwn.net>, x86@kernel.org,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
        Borislav Petkov <bp@suse.de>, Andy Lutomirski <luto@kernel.org>,
        linux-doc@vger.kernel.org, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com
Subject: Re: [PATCH] Prefer kASLR over Hibernation
References: <20160406194404.GA11150@www.outflux.net>
In-Reply-To: <20160406194404.GA11150@www.outflux.net>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Hi Kees,

On 06/04/16 20:44, Kees Cook wrote:
> When building with both CONFIG_HIBERNATION and CONFIG_RANDOMIZE_BASE,
> one or the other must be chosen at boot-time. Until now, hibernation
> was selected when no choice was made on the command line.
> 
> To make the security benefits of kASLR more widely available to end
> users (since the use of hibernation is becoming more rare and kASLR,
> already available on x86, will be available on arm64 and MIPS soon),
> this changes the default to preferring kASLR over hibernation. Users
> wanting hibernation can turn off kASLR by adding "nokaslr" to the kernel
> command line.

While hibernate isn't yet merged for arm64, it does work with kASLR in v4.6-rc*,
it would be a shame to have to choose at boot time, (but that's my problem to
fix if/when its merged).


> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index fca9254280ee..be5041354b1e 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -1159,6 +1164,13 @@ static int __init kaslr_nohibernate_setup(char *str)
>  	return nohibernate_setup(str);
>  }
>  
> +static int __init nokaslr_hibernate_setup(char *str)
> +{
> +	noresume = 0;
> +	nohibernate = 0;
> +	return 1;
> +}
> +
>  static int __init page_poison_nohibernate_setup(char *str)
>  {
>  #ifdef CONFIG_PAGE_POISONING_ZERO
> @@ -1183,4 +1195,5 @@ __setup("resumewait", resumewait_setup);
>  __setup("resumedelay=", resumedelay_setup);
>  __setup("nohibernate", nohibernate_setup);
>  __setup("kaslr", kaslr_nohibernate_setup);
> +__setup("nokaslr", nokaslr_hibernate_setup);

So one or the other option has to be specified at boot?

The kASLR patches for arm64 in v4.6-rc1 enable kASLR at boot if you chose to
select it at compile time. I guess this patch is preparation for doing the same
on x86?

I didn't hit this kaslr_nohibernate_setup() call during testing because of the
on by default behaviour. Is it worth exposing this via Kconfig? Something like:
ARCH_RANDOMIZE_BASE_DEFAULT_ON ?


Thanks,

James