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

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Date:	Sun, 26 Jan 2014 16:20:33 +0800
From:	Ren Qiaowei <qiaowei.ren@...el.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/4] Intel MPX support

On 01/26/2014 04:19 PM, Ingo Molnar wrote:
>
> * Qiaowei Ren <qiaowei.ren@...el.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?
>
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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