linux-kernel - Re: [PATCH] [x86] detect and report lack of NX protections

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Date:	Tue, 20 Oct 2009 08:43:35 +0900
From:	Arjan van de Ven <arjan@...radead.org>
To:	Kees Cook <kees.cook@...onical.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Pekka Enberg <penberg@...helsinki.fi>,
	Jan Beulich <jbeulich@...ell.com>,
	Vegard Nossum <vegardno@....uio.no>,
	Yinghai Lu <yinghai@...nel.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [x86] detect and report lack of NX protections

On Mon, 19 Oct 2009 11:42:34 -0700
Kees Cook <kees.cook@...onical.com> wrote:

> It is possible for x86_64 systems to lack the NX bit (see
> check_efer()) either due to the hardware lacking support or the BIOS
> having turned off the CPU capability, so NX status should be
> reported.  Additionally, anyone booting NX-capable CPUs in 32bit mode
> without PAE will lack NX functionality, so this change provides
> feedback for that case as well.
> 
> Signed-off-by: Kees Cook <kees.cook@...onical.com>
> ---
>  arch/x86/mm/init.c     |   10 ++++++++++
>  arch/x86/mm/setup_nx.c |    2 ++
>  2 files changed, 12 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index 73ffd55..8472293 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -149,6 +149,16 @@ unsigned long __init_refok
> init_memory_mapping(unsigned long start, set_nx();
>  	if (nx_enabled)
>  		printk(KERN_INFO "NX (Execute Disable) protection:
> active\n");
> +	else if (cpu_has_pae)
> +#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
> +		/* PAE kernel, PAE CPU, without NX */
> +		printk(KERN_WARNING "Warning: NX (Execute Disable)
> protection "
> +		       "missing in CPU or disabled in BIOS!\n");
> +#else
> +		/* 32bit non-PAE kernel, PAE CPU */
> +		printk(KERN_WARNING "Warning: NX (Execute Disable)
> protection "
> +		       "cannot be enabled: non-PAE kernel!\n");
> +#endif

can we please not use "Warning" for something like this in the
message...

lets keep "Warning" for real WARN_ON() kind of events.
--
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