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Subject[PATCH 3/3] x86/mpx: remove MPX APIs
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From: Dave Hansen <dave.hansen@linux.intel.com>

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@linux.intel.com>
Cc: x86@kernel.org
Cc: Andy Lutomirski <luto@kernel.org>
---

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;
_
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