From 8c3641e957a948f41f0174290096ed7a3b95e703 Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Sun, 7 Jun 2015 11:37:02 -0700 Subject: [PATCH] x86/mpx: Introduce a boot-time disable flag 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 Reviewed-by: Thomas Gleixner Cc: Dave Hansen Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20150607183702.2E8B77AB@viggo.jf.intel.com Signed-off-by: Ingo Molnar --- Documentation/kernel-parameters.txt | 4 ++++ arch/x86/kernel/cpu/common.c | 16 ++++++++++++++++ 2 files changed, 20 insertions(+) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 61ab1628a057..8b7e5c342302 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -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 diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 401ccb03054e..3956858e5312 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -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;