[PATCH 2/2] x86, mpx: Give MPX a real config option prompt

From: Dave Hansen
Date: Fri Dec 12 2014 - 13:38:39 EST

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

Give MPX a real config option. The CPUs that support it
(referenced here):


are not available publicly, so we need to make it somewhat
easy to disable.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

b/Documentation/x86/intel_mpx.txt | 6 +++++-
b/arch/x86/Kconfig | 30 ++++++++++++++++++++++++++----
2 files changed, 31 insertions(+), 5 deletions(-)

diff -puN arch/x86/Kconfig~x86-mpx-real-config-option-v4 arch/x86/Kconfig
--- a/arch/x86/Kconfig~x86-mpx-real-config-option-v4 2014-12-12 10:12:53.531938223 -0800
+++ b/arch/x86/Kconfig 2014-12-12 10:12:53.536938449 -0800
@@ -248,10 +248,6 @@ config HAVE_INTEL_TXT
def_bool y
depends on INTEL_IOMMU && ACPI

-config X86_INTEL_MPX
- def_bool y
- depends on CPU_SUP_INTEL
config X86_32_SMP
def_bool y
depends on X86_32 && SMP
@@ -1593,6 +1589,32 @@ config X86_SMAP

If unsure, say Y.

+config X86_INTEL_MPX
+ prompt "Intel MPX (Memory Protection Extensions)"
+ def_bool y
+ depends on CPU_SUP_INTEL
+ ---help---
+ MPX provides hardware features that can be used in
+ conjunction with compiler-instrumented code to check
+ memory references. It is designed to detect buffer
+ overflow or underflow bugs.
+ This option enables running applications which are
+ instrumented or otherwise use MPX. It does not use MPX
+ itself inside the kernel or to protect the kernel
+ against bad memory references.
+ Enabling this option will make the kernel larger:
+ ~8k of kernel text and 36 bytes of data on a 64-bit
+ defconfig. It adds a long to the 'mm_struct' which
+ will increase the kernel memory overhead of each
+ process and adds some branches to paths used during
+ exec() and munmap().
+ For details, see Documentation/x86/intel_mpx.txt
+ If unsure, say Y.
config EFI
bool "EFI runtime service support"
depends on ACPI
diff -puN Documentation/x86/intel_mpx.txt~x86-mpx-real-config-option-v4 Documentation/x86/intel_mpx.txt
--- a/Documentation/x86/intel_mpx.txt~x86-mpx-real-config-option-v4 2014-12-12 10:12:53.532938268 -0800
+++ b/Documentation/x86/intel_mpx.txt 2014-12-12 10:12:53.537938494 -0800
@@ -7,11 +7,15 @@ that can be used in conjunction with com
references, for those references whose compile-time normal intentions are
usurped at runtime due to buffer overflow or underflow.

+You can tell if your CPU supports MPX by looking in /proc/cpuinfo:
+ cat /proc/cpuinfo | grep ' mpx '
For more information, please refer to Intel(R) Architecture Instruction
Set Extensions Programming Reference, Chapter 9: Intel(R) Memory Protection

-Note: Currently no hardware with MPX ISA is available but it is always
+Note: As of December 2014, no hardware with MPX is available but it is
possible to use SDE (Intel(R) Software Development Emulator) instead, which
can be downloaded from
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