x86/mpx: Introduce a boot-time disable flag (8c3641e9) · Commits · 戴 / test

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>

Documentation/kernel-parameters.txt

+4 −0

Original line number	Diff line number	Diff line
		@@ -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

arch/x86/kernel/cpu/common.c

+16 −0

Original line number	Diff line number	Diff line
		@@ -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;

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