linux-kernel - Re: [RFC][PATCH 0/8] x86, mpx: Support 32-bit binaries on 64-bit kernels

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Date:	Fri, 12 Dec 2014 12:22:13 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Dave Hansen <dave@...1.net>, linux-kernel@...r.kernel.org
CC:	tglx@...utronix.de, x86@...nel.org
Subject: Re: [RFC][PATCH 0/8] x86, mpx: Support 32-bit binaries on 64-bit
 kernels

On 12/12/2014 11:12 AM, Dave Hansen wrote:
> This is 3.20 material.  I'm hoping to get some comments early
> in case folks have some issues with the way it's being done.
>
> --
>
> The MPX hardware structures differ in layout in 32 and 64-bit
> mode.  A 32-bit binary running on a 64-bit kernel needs the
> 32-bit structures, so we need code which switches between
> the two modes.

The OS community figured out years ago that you aren't supposed to do 
this.  Did everyone forget to tell the hardware people?

:(

--Andy

>
> The first patch is just a documentation update.  The next 5
> patches are really just prepwork.  The meat is in the last 3.
>
> 	x86: make is_64bit_mm() widely available
> 	x86: make __VIRTUAL_MASK safe to use on 32 bit
> 	x86, mpx: we do not allocate the bounds directory
> 	x86, mpx: remove redundant MPX_BNDCFG_ADDR_MASK
> 	x86, mpx: Add temporary variable to reduce masking
> 	x86, mpx: new directory entry to addr helper
> 	x86, mpx: do 32-bit-only cmpxchg for 32-bit apps
> 	x86, mpx: support 32bit binaries on 64bit kernel
>
>   Documentation/x86/intel_mpx.txt    |   12 +++-
>   arch/x86/include/asm/mmu_context.h |   13 +++++
>   arch/x86/include/asm/mpx.h         |    2
>   arch/x86/include/asm/page_types.h  |    8 +++
>   arch/x86/kernel/uprobes.c          |   10 ---
>   arch/x86/mm/mpx.c                  |   93 ++++++++++++++++++++++++++++++-------
>   6 files changed, 107 insertions(+), 31 deletions(-)
>

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