Date: Sun, 26 Jan 2014 09:19:12 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Qiaowei Ren <qiaowei.ren@intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 0/4] Intel MPX support
Message-ID: <20140126081912.GA28831@gmail.com>
References: <1390727338-20487-1-git-send-email-qiaowei.ren@intel.com>
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* Qiaowei Ren <qiaowei.ren@intel.com> 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?

> 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,

	Ingo
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