linux-kernel - Re: [PATCH 08/17] x86, mpx: boot-time disable

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Date:	Fri, 27 Mar 2015 16:07:43 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Dave Hansen <dave@...1.net>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
	dave.hansen@...ux.intel.com
Subject: Re: [PATCH 08/17] x86, mpx: boot-time disable

On Thu, Mar 26, 2015 at 11:33:43AM -0700, Dave Hansen wrote:
> 
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> MPX has the _potential_ to cause some issues.  Say part of your init
> system tried to protect one of its components from buffer overflows
> with MPX.  If there were a false positive, it's possible that MPX
> could keep a system from booting.
> 
> MPX could also potentially cause performance issues since it is
> present in hot paths like the unmap path.
> 
> Allow it to be disabled at boot time.
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> ---
> 
>  b/Documentation/kernel-parameters.txt |    4 ++++
>  b/arch/x86/kernel/cpu/common.c        |   16 ++++++++++++++++
>  2 files changed, 20 insertions(+)
> 
> diff -puN arch/x86/kernel/cpu/common.c~x86-mpx-disable-boot-time arch/x86/kernel/cpu/common.c
> --- a/arch/x86/kernel/cpu/common.c~x86-mpx-disable-boot-time	2015-03-26 11:27:31.269400935 -0700
> +++ b/arch/x86/kernel/cpu/common.c	2015-03-26 11:27:31.275401206 -0700
> @@ -172,6 +172,22 @@ static int __init x86_xsaves_setup(char
>  }
>  __setup("noxsaves", x86_xsaves_setup);
>  
> +static int __init x86_mpx_setup(char *s)
> +{
> +	/* require an exact match without trailing characters */
> +	if (strlen(s))
> +		return 0;
> +
> +	/* do not emit a message if the feature is not present */
> +	if (!boot_cpu_has(X86_FEATURE_MPX))
> +		return 1;
> +
> +	setup_clear_cpu_cap(X86_FEATURE_MPX);
> +	printk("nompx: Intel Memory Protection Extensions (MPX) disabled\n");

WARNING: printk() should include KERN_ facility level
#52: FILE: arch/x86/kernel/cpu/common.c:186:
+       printk("nompx: Intel Memory Protection Extensions (MPX) disabled\n");

checkpatch is sometimes right.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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