Re: [PATCH v3 0/4] Intel MPX support

[Ren Qiaowei]

On 01/26/2014 04:19 PM, Ingo Molnar wrote:
> * Qiaowei Ren <qiaowei.ren@xxxxxxxxx> wrote:
>
> > 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
> > performance.
> >
> > 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
> > (http://gcc.gnu.org/svn.html) 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.
>
> AFAICS the kernel side implementation causes no runtime overhead for
> non-MPX workloads, and also causes no runtime overhead for non-MPX
> hardware, right?
Yes.

> > 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
> > http://software.intel.com/en-us/articles/intel-software-development-emulator
> >
> >
> > 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.
> >
> > Qiaowei Ren (4):
> >    x86, mpx: add documentation on Intel MPX
> >    x86, mpx: hook #BR exception handler to allocate bound tables
> >    x86, mpx: add prctl commands PR_MPX_INIT, PR_MPX_RELEASE
> >    x86, mpx: extend siginfo structure to include bound violation
> >      information
> >
> >   Documentation/x86/intel_mpx.txt    |  226 ++++++++++++++++++++
> >   arch/x86/Kconfig                   |    4 +
> >   arch/x86/include/asm/mpx.h         |   63 ++++++
> >   arch/x86/include/asm/processor.h   |   16 ++
> >   arch/x86/kernel/Makefile           |    1 +
> >   arch/x86/kernel/mpx.c              |  415 ++++++++++++++++++++++++++++++++++++
> >   arch/x86/kernel/traps.c            |   61 +++++-
> >   include/uapi/asm-generic/siginfo.h |    9 +-
> >   include/uapi/linux/prctl.h         |    6 +
> >   kernel/signal.c                    |    4 +
> >   kernel/sys.c                       |   12 +
> >   11 files changed, 815 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
>
> Ok, this summary was pretty good - it addresses my prior objections
> wrt. submission quality. Once the details are fleshed out this sure
> looks like a useful feature.
Thanks. I apologize for previous submission.

Thanks,
Qiaowei
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