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Date: Tue, 25 Jul 2017 10:16:38 +0300
From: Hans Liljestrand <>
To: Kees Cook <>
Cc: "" <>,
	"Reshetova, Elena" <>,
	Dave Hansen <>,
	"H. Peter Anvin" <>
Subject: Re: [RFC PATCH 2/5] gcc-plugins: adds MPXK gcc plugin

On Mon, Jul 24, 2017 at 07:40:57PM -0700, Kees Cook wrote:
>On Mon, Jul 24, 2017 at 6:38 AM, Hans Liljestrand
><> wrote:
>> Adds a gcc-plugin that modifies vanilla GCC MPX instrumentation for
>> in-kernel use. Also adds MPXK_CFLAGS Makefile variable that can be used to
>> selectively enable MPXK for specific kernel objects. This plugin is not
>> enabled kernel-wide and must be explicitly enabled in the appropriate
>> Makefile.
>> The purpose of the plugin is to replace BNDSTX+BNDLDX bound storage with
>> our own mpxk_load_bounds function and to replace memory mainpulating
>> function with corresponding wrapper function. The plugin accomplishes
>> this via the following tasks:
>> - It adds MPXK-wrappers functions for memory altering functions, e.g.
>>   kmalloc, memcpy, etc. This is needed both to check bounds for input
>>   argument pointers and properly set bounds for returned pointers. This
>>   is done by the mpxk_wrappers compiler pass. (This could potentially
>>   be done, for better performance, by direct instrumentation at the call
>>   site.)
>> - Replace BNDLDX calls with mpxk_load_bounds function calls. This
>>   includes two separate cases: free-standing loads handled by the
>>   mpxk_bnd_store pass, and loads in function prologues that are handled
>>   by the mpxk_cfun_args pass. These are needed for situation where the
>>   compile time instrumentation cannot determine a way to statically
>>   propagate the bounds via the stack or registers.
>> - The final mpxk_pass_sweeper removes any remaining BNDLDX/BNDSTX calls.
>Since this creates multiple files for a single plugin, can you instead
>relocate these into a subdirectory (which should be supported by the
>build system already).

Thanks. I was a bit unsure how to organize these in the first place, but a
subdirectory sounds like a good idea. I'll also look at consolidating the 
non-pass files into one.


>Kees Cook
>Pixel Security

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