Re: [GIT pull] x86 mpx support for 3.19

[Dave Hansen]

On 12/10/2014 11:05 AM, Linus Torvalds wrote:
> On Tue, Dec 9, 2014 at 6:08 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> Why would I want to enable this in my kernel when there are no actual
> CPU's out yet that support it? And even when there are, why would I do
> it if the CPU I have doesn't support it?

There's no good reason to enable it except for testing (compile, or
making sure we didn't screw up the #BR code for CPUs without MPX).

Patch is attached to add the following:

> config X86_INTEL_MPX
>         prompt "Intel MPX (Memory Protection Extensions)" if EXPERT
>         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.
> 
>           Enabling this option will make the kernel larger and
>           slightly increase the size of some data structures.
> 
>           If unsure, say Y.



From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

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, so we need to make it somewhat
easy to disable.

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

 b/arch/x86/Kconfig |   19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff -puN arch/x86/Kconfig~x86-mpx-real-config-option arch/x86/Kconfig
--- a/arch/x86/Kconfig~x86-mpx-real-config-option	2014-12-10 11:19:13.638835732 -0800
+++ b/arch/x86/Kconfig	2014-12-10 11:30:27.080209235 -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
@@ -1575,6 +1571,21 @@ config X86_SMAP
 
 	  If unsure, say Y.
 
+config X86_INTEL_MPX
+	prompt "Intel MPX (Memory Protection Extensions)" if EXPERT
+	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.
+
+	  Enabling this option will make the kernel larger and
+	  slightly increase the size of some data structures.
+
+	  If unsure, say Y.
+
 config EFI
 	bool "EFI runtime service support"
 	depends on ACPI
_