[PATCH 3/3] x86/mpx: remove MPX APIs

[Dave Hansen]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

MPX is being removed from the kernel due to a lack of support
in the toolchain going forward (gcc).

The first thing we need to do is remove the userspace-visible
ABIs so that applications will stop using it.  The most visible
one are the enable/disable prctl()s.  Remove them first.

This is the most minimal and least invasive patch needed to
ensure that apps stop using MPX with new kernels.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
---

 b/include/uapi/linux/prctl.h |    2 +-
 b/kernel/sys.c               |   16 ++--------------
 2 files changed, 3 insertions(+), 15 deletions(-)

diff -puN include/uapi/linux/prctl.h~mpx-remove-apis include/uapi/linux/prctl.h
--- a/include/uapi/linux/prctl.h~mpx-remove-apis	2019-07-05 10:40:49.441907046 -0700
+++ b/include/uapi/linux/prctl.h	2019-07-05 10:40:49.447907046 -0700
@@ -181,7 +181,7 @@ struct prctl_mm_map {
 #define PR_GET_THP_DISABLE	42
 
 /*
- * Tell the kernel to start/stop helping userspace manage bounds tables.
+ * No longer implemented, but left here to ensure the numbers stay reserved:
  */
 #define PR_MPX_ENABLE_MANAGEMENT  43
 #define PR_MPX_DISABLE_MANAGEMENT 44
diff -puN kernel/sys.c~mpx-remove-apis kernel/sys.c
--- a/kernel/sys.c~mpx-remove-apis	2019-07-05 10:40:49.444907046 -0700
+++ b/kernel/sys.c	2019-07-05 10:40:49.448907046 -0700
@@ -103,12 +103,6 @@
 #ifndef SET_TSC_CTL
 # define SET_TSC_CTL(a)		(-EINVAL)
 #endif
-#ifndef MPX_ENABLE_MANAGEMENT
-# define MPX_ENABLE_MANAGEMENT()	(-EINVAL)
-#endif
-#ifndef MPX_DISABLE_MANAGEMENT
-# define MPX_DISABLE_MANAGEMENT()	(-EINVAL)
-#endif
 #ifndef GET_FP_MODE
 # define GET_FP_MODE(a)		(-EINVAL)
 #endif
@@ -2456,15 +2450,9 @@ SYSCALL_DEFINE5(prctl, int, option, unsi
 		up_write(&me->mm->mmap_sem);
 		break;
 	case PR_MPX_ENABLE_MANAGEMENT:
-		if (arg2 || arg3 || arg4 || arg5)
-			return -EINVAL;
-		error = MPX_ENABLE_MANAGEMENT();
-		break;
 	case PR_MPX_DISABLE_MANAGEMENT:
-		if (arg2 || arg3 || arg4 || arg5)
-			return -EINVAL;
-		error = MPX_DISABLE_MANAGEMENT();
-		break;
+		/* No longer implemented: */
+		return -EINVAL;
 	case PR_SET_FP_MODE:
 		error = SET_FP_MODE(me, arg2);
 		break;
_