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

tip-bot for Dave Hansen
2014-12-15T15:02:17Z

Commit-ID: 72e9b5fe9bee0826e7ce7599adbdc64e544780ef
Gitweb: http://git.kernel.org/tip/72e9b5fe9bee0826e7ce7599adbdc64e544780ef
Author: Dave Hansen <dave.hansen@linux.intel.com>
AuthorDate: Fri, 12 Dec 2014 10:38:36 -0800
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Mon, 15 Dec 2014 15:58:57 +0100

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

diff --git a/Documentation/x86/intel_mpx.txt b/Documentation/x86/intel_mpx.txt
index 6ca6e2b..818518a 100644
--- 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
--- 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