linux-kernel - Re: [PATCH] x86, mpx: Ensure unused arguments of prctl() MPX requests are 0

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Date:	Sat, 10 Jan 2015 14:49:07 +0100
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <andi@...stfloor.org>
CC:	mtk.manpages@...il.com, Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Qiaowei Ren <qiaowei.ren@...el.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86, mpx: Ensure unused arguments of prctl() MPX requests
 are 0

On 01/09/2015 07:34 PM, Dave Hansen wrote:
> On 01/09/2015 10:25 AM, Michael Kerrisk (man-pages) wrote:
>> On 9 January 2015 at 18:25, Andi Kleen <andi@...stfloor.org> wrote:
>>> "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com> writes:
>>>> From: Michael Kerrisk <mtk.manpages@...il.com>
>>>>
>>>> commit fe8c7f5cbf91124987106faa3bdf0c8b955c4cf7 added two new prctl()
>>>> operations, PR_MPX_ENABLE_MANAGEMENT and PR_MPX_DISABLE_MANAGEMENT.
>>>> However, no checks were included to ensure that unused arguments
>>>> are zero, as is done in many existing prctl()s and as should be
>>>> done for all new prctl()s. This patch adds the required checks.
>>>
>>> This will break the existing gcc run time, which doesn't zero these
>>> arguments.
>>
>> I'm a little lost here. Weren't these flags new in the
>> as-yet-unreleased 3.19? How does gcc run-time depends on them already?
> 
> These prctl()s have been around in some form or another for a few months
> since the patches had not yet been merged in to the kernel.  There is
> support for them in a set of (yet unmerged) gcc patches, as well as some
> tests which are only internal to Intel.
> 
> This change will, indeed, break those internal tests as well as the gcc
> patches.  As far as I know, the code is not in production anywhere and
> can be changed.  The prctl() numbers have changed while the patches were
> out of tree and it's a somewhat painful process each time it changes.
> It's not impossible, just painful.

So, sounds like thinks can be fixed (with mild inconvenience), and they
should be fixed before 3.19 is actually released.

Cheers,

Michael



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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