x86, mpx: Give MPX a real config option prompt

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

  https://software.intel.com/en-us/forums/topic/402393

are not available publicly yet. Right now only the software emulator
provides MPX for the general public.

[ tglx: Make it default off. There is no point in having it on right
        now as no hardware and no proper tooling support are available ]

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dave Hansen <dave@sr71.net>
Link: http://lkml.kernel.org/r/20141212183836.2569D58D@viggo.jf.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 26 insertions, 4 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 967dfe0ba85e..cc91e5e55d13 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -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
@@ -1575,6 +1571,32 @@ config X86_SMAP
 
           If unsure, say Y.
 
+config X86_INTEL_MPX
+        prompt "Intel MPX (Memory Protection Extensions)"
+        def_bool n
+        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 N.
+
 config EFI
         bool "EFI runtime service support"
         depends on ACPI