linux-kernel - Re: [PATCH] x86: Configure NX support earlier in setup

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Message-ID: <53BC7210.1000305@gmail.com>
Date:	Tue, 08 Jul 2014 17:34:56 -0500
From:	Stuart Hayes <stuart.w.hayes@...il.com>
To:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, x86@...nel.org
CC:	linux-kernel@...r.kernel.org, matt.fleming@...el.com, bp@...e.de
Subject: Re: [PATCH] x86: Configure NX support earlier in setup_arch

On 7/2/2014 8:47 PM, Stuart Hayes wrote:

> A page fault can crash the kernel very early if an NX bit is set in a
> page table entry, if the CPU doesn't support NX (or if NX support is
> disabled in the CPU).  Move the call to x86_configure_nx() earlier
> than parse_setup_data(), since that calls early_memremap().
> 
> Signed-off-by: Stuart Hayes <stuart.w.hayes@...il.com>
> ---
> 
> --- linux-3.16-rc3/arch/x86/kernel/setup.c.orig	2014-07-02 12:14:50.196308719 -0400
> +++ linux-3.16-rc3/arch/x86/kernel/setup.c	2014-07-02 12:11:11.240301228 -0400
> @@ -940,6 +940,17 @@ void __init setup_arch(char **cmdline_p)
>  
>  	iomem_resource.end = (1ULL << boot_cpu_data.x86_phys_bits) - 1;
>  	setup_memory_map();
> +
> +	/*
> +	 * x86_configure_nx() is called before parse_setup_data() to detect
> +	 * whether hardware doesn't support NX (so that parse_setup_data()
> +	 * can safely call early_memremap() without setting the XD bit in
> +	 * the PTE, which can cause an unrecoverable page fault). It may
> +	 * then be called again from within noexec_setup() during parsing
> +	 * early parameters to honor the respective command line option.
> +	 */
> +	x86_configure_nx();
> +
>  	parse_setup_data();
>  
>  	copy_edd();
> @@ -974,15 +985,6 @@ void __init setup_arch(char **cmdline_p)
>  	strlcpy(command_line, boot_command_line, COMMAND_LINE_SIZE);
>  	*cmdline_p = command_line;
>  
> -	/*
> -	 * x86_configure_nx() is called before parse_early_param() to detect
> -	 * whether hardware doesn't support NX (so that the early EHCI debug
> -	 * console setup can safely call set_fixmap()). It may then be called
> -	 * again from within noexec_setup() during parsing early parameters
> -	 * to honor the respective command line option.
> -	 */
> -	x86_configure_nx();
> -
>  	parse_early_param();
>  
>  	x86_report_nx();


I haven't received any responses... is there a problem with the patch?  Also CCing a couple people.

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