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Intel MPX support

From:  Qiaowei Ren <>
To:  "H. Peter Anvin" <>, Thomas Gleixner <>, Ingo Molnar <>, Dave Hansen <>
Subject:  [PATCH v6 00/10] Intel MPX support
Date:  Wed, 18 Jun 2014 17:44:06 +0800
Message-ID:  <>
Cc:,, Qiaowei Ren <>
Archive-link:  Article

This patchset adds support for the Memory Protection Extensions
(MPX) feature found in future Intel processors.

MPX 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.

MPX provides this capability at very low performance overhead for
newly compiled code, and provides compatibility mechanisms with legacy
software components. MPX architecture is designed allow a machine to
run both MPX enabled software and legacy software that is MPX unaware.
In such a case, the legacy software does not benefit from MPX, but it
also does not experience any change in functionality or reduction in

More information about Intel MPX can be found in "Intel(R) Architecture
Instruction Set Extensions Programming Reference".

To get the advantage of MPX, changes are required in the OS kernel,
binutils, compiler, system libraries support.

New GCC option -fmpx is introduced to utilize MPX instructions.
Currently GCC compiler sources with MPX support is available in a
separate branch in common GCC SVN repository. See GCC SVN page
( for details.

To have the full protection, we had to add MPX instrumentation to all
the necessary Glibc routines (e.g. memcpy) written on assembler, and
compile Glibc with the MPX enabled GCC compiler. Currently MPX enabled
Glibc source can be found in Glibc git repository.

Enabling an application to use MPX will generally not require source
code updates but there is some runtime code, which is responsible for
configuring and enabling MPX, needed in order to make use of MPX.
For most applications this runtime support will be available by linking
to a library supplied by the compiler or possibly it will come directly
from the OS once OS versions that support MPX are available.

MPX kernel code, namely this patchset, has mainly the 2 responsibilities:
provide handlers for bounds faults (#BR), and manage bounds memory.

The high-level areas modified in the patchset are as follow:
1) struct siginfo is extended to include bound violation information.
2) two prctl() commands are added to do performance optimization.

Currently no hardware with MPX ISA is available but it is always
possible to use SDE (Intel(R) software Development Emulator) instead,
which can be downloaded from

Future TODO items:
1) support 32-bit binaries on 64-bit kernels.

Changes since v1:
  * check to see if #BR occurred in userspace or kernel space.
  * use generic structure and macro as much as possible when
    decode mpx instructions.

Changes since v2:
  * fix some compile warnings.
  * update documentation.

Changes since v3:
  * correct some syntax errors at documentation, and document
    extended struct siginfo.
  * for kill the process when the error code of BNDSTATUS is 3.
  * add some comments.
  * remove new prctl() commands.
  * fix some compile warnings for 32-bit.

Changes since v4:
  * raise SIGBUS if the allocations of the bound tables fail.

Changes since v5:
  * hook unmap() path to cleanup unused bounds tables, and use
    new prctl() command to register bounds directory address to
    struct mm_struct to check whether one process is MPX enabled
    during unmap().
  * in order track precisely MPX memory usage, add MPX specific
    mmap interface and one VM_MPX flag to check whether a VMA
    is MPX bounds table.
  * add macro cpu_has_mpx to do performance optimization.
  * sync struct figinfo for mips with general version to avoid
    build issue.

Qiaowei Ren (10):
  x86, mpx: introduce VM_MPX to indicate that a VMA is MPX specific
  x86, mpx: add MPX specific mmap interface
  x86, mpx: add macro cpu_has_mpx
  x86, mpx: hook #BR exception handler to allocate bound tables
  x86, mpx: extend siginfo structure to include bound violation
  mips: sync struct siginfo with general version
  x86, mpx: decode MPX instruction to get bound violation information
  x86, mpx: add prctl commands PR_MPX_REGISTER, PR_MPX_UNREGISTER
  x86, mpx: cleanup unused bound tables
  x86, mpx: add documentation on Intel MPX

 Documentation/x86/intel_mpx.txt      |  127 +++++++++++
 arch/mips/include/uapi/asm/siginfo.h |    4 +
 arch/x86/Kconfig                     |    4 +
 arch/x86/include/asm/cpufeature.h    |    6 +
 arch/x86/include/asm/mmu_context.h   |   16 ++
 arch/x86/include/asm/mpx.h           |   91 ++++++++
 arch/x86/include/asm/processor.h     |   18 ++
 arch/x86/kernel/Makefile             |    1 +
 arch/x86/kernel/mpx.c                |  413 ++++++++++++++++++++++++++++++++++
 arch/x86/kernel/traps.c              |   62 +++++-
 arch/x86/mm/Makefile                 |    2 +
 arch/x86/mm/init_64.c                |    2 +
 arch/x86/mm/mpx.c                    |  247 ++++++++++++++++++++
 fs/proc/task_mmu.c                   |    1 +
 include/asm-generic/mmu_context.h    |    6 +
 include/linux/mm.h                   |    2 +
 include/linux/mm_types.h             |    3 +
 include/uapi/asm-generic/siginfo.h   |    9 +-
 include/uapi/linux/prctl.h           |    6 +
 kernel/signal.c                      |    4 +
 kernel/sys.c                         |   12 +
 mm/mmap.c                            |    2 +
 22 files changed, 1036 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/x86/intel_mpx.txt
 create mode 100644 arch/x86/include/asm/mpx.h
 create mode 100644 arch/x86/kernel/mpx.c
 create mode 100644 arch/x86/mm/mpx.c

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