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

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Message-ID: <alpine.DEB.2.02.1401252010400.10325@chino.kir.corp.google.com>
Date:	Sat, 25 Jan 2014 20:22:58 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Qiaowei Ren <qiaowei.ren@...el.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 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.