linux-kernel - Re: [PATCH v3 4/4] x86, mpx: extend siginfo structure to include bound violation information

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Date:	Sun, 26 Jan 2014 12:39:55 +0800
From:	Ren Qiaowei <qiaowei.ren@...el.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/4] x86, mpx: extend siginfo structure to include
 bound violation information

On 01/26/2014 12:22 PM, David Rientjes wrote:
> On Sun, 26 Jan 2014, Qiaowei Ren wrote:
>
>> This patch adds new fields about bound violation into siginfo
>> structure. si_lower and si_upper are respectively lower bound
>> and upper bound when bound violation is caused.
>>
>> These fields will be set in #BR exception handler by decoding
>> the user instruction and constructing the faulting pointer.
>> A userspace application can get violation address, lower bound
>> and upper bound for bound violation from this new siginfo structure.
>>
>> Signed-off-by: Qiaowei Ren <qiaowei.ren@...el.com>
>
> Same 32-bit warnings I reported for v2:
>
> arch/x86/kernel/mpx.c: In function ‘do_mpx_bounds’:
> arch/x86/kernel/mpx.c:407:3: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
> arch/x86/kernel/mpx.c:409:3: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
>
> and the documentation says you explicitly want to support this config.
>
> These types of warnings are usually indicative of real problems when
> you're storing upper and lower bits in 32-bit fields after casting them
> from 64-bit values.
>
> I'm also not sure if the added fields to the generic struct siginfo can be
> justified for this.
>
According to MPX spec, for 32-bit case, the upper 32-bits of 64-bits 
bound register are ignored, and so casting to pointer from 64-bit values 
should be not produce any problems.

Thanks,
Qiaowei
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