linux-kernel - Re: [PATCH v3 3/4] x86, mpx: add prctl commands PR_MPX_INIT, PR_MPX

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Date:	Mon, 27 Jan 2014 13:54:01 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>,
	Ren Qiaowei <qiaowei.ren@...el.com>,
	Ingo Molnar <mingo@...nel.org>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH v3 3/4] x86, mpx: add prctl commands PR_MPX_INIT, PR_MPX_RELEASE

On 01/26/2014 06:10 PM, H. Peter Anvin wrote:
> On 01/26/2014 05:55 PM, Ren Qiaowei wrote:
>>
>> Peter, you mean we should remove these two call and do what they do in
>> user-space, right?
>>
> 
> Unless we think there is a benefit to the kernel to have a on/off switch
> for the #BR exception (if disabled, all #BR exceptions are signals,
> regardless of source.)

Yes.

For example, wouldn't UML want to have all of this stuff disabled?
Presumably it would much prefer to receive the exception directly.

The same goes for seccomp users -- as it currently stands, this code
allows mmap without a system call.

This probably means that the prctl should (optionally) take a parameter
that fixes the address of the L1 table -- seccomp users would probably
want that.  (Actually, everyone might -- this is going to have weird
results if the L1 table moves.)

--Andy

> 
> There might be, would like other people's opinion.
> 
> 	-hpa
> 
> 

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