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x86/mpx: Introduce a boot-time disable flag

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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>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave@sr71.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150607183702.2E8B77AB@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Dave Hansen 2015-06-07 11:37:02 -07:00 committed by Ingo Molnar
parent eb099e5bc5
commit 8c3641e957
2 changed files with 20 additions and 0 deletions
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4
Documentation/kernel-parameters.txt
View File

@ -937,6 +937,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
Enable debug messages at boot time. See
Documentation/dynamic-debug-howto.txt for details.
nompx [X86] Disables Intel Memory Protection Extensions.
See Documentation/x86/intel_mpx.txt for more
information about the feature.
eagerfpu= [X86]
on enable eager fpu restore
off disable eager fpu restore

16
arch/x86/kernel/cpu/common.c
View File

@ -144,6 +144,22 @@ DEFINE_PER_CPU_PAGE_ALIGNED(struct gdt_page, gdt_page) = { .gdt = {
} };
EXPORT_PER_CPU_SYMBOL_GPL(gdt_page);
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);
pr_info("nompx: Intel Memory Protection Extensions (MPX) disabled\n");
return 1;
}
__setup("nompx", x86_mpx_setup);
#ifdef CONFIG_X86_32
static int cachesize_override = -1;
static int disable_x86_serial_nr = 1;