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>

diff --git a/Documentation/x86/intel_mpx.txt b/Documentation/x86/intel_mpx.txt
index 6ca6e2b..818518a 100644 (file)
--- a/Documentation/x86/intel_mpx.txt
+++ b/Documentation/x86/intel_mpx.txt
@@ -7,11 +7,15 @@ that can be used in conjunction with compiler changes to check memory
 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
 Extensions.
 
-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
 http://software.intel.com/en-us/articles/intel-software-development-emulator

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 967dfe0..cc91e5e 100644 (file)
--- 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