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

Borislav Petkov
2015-03-27T15:09:37Z

On Thu, Mar 26, 2015 at 11:33:43AM -0700, Dave Hansen wrote:
>
> From: Dave Hansen <dave.hansen@linux.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@linux.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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