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

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Message-ID: <52E6D72B.1060005@zytor.com>
Date:	Mon, 27 Jan 2014 14:01:15 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>,
	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 01/27/2014 01:54 PM, Andy Lutomirski wrote:
> 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.)
> 

That seems like a good argument.  If the table has been moved by
userspace we can deliver the signal as a violation.

	-hpa


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