From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ville =?iso-8859-1?Q?Syrj=E4l=E4?= <ville.syrjala@linux.intel.com>
Subject: Re: [PATCH] drm/i915: Add to_user_ptr()
Date: Mon, 25 Feb 2013 12:58:01 +0200
Message-ID: <20130225105801.GQ4469@intel.com>
References: <1361542371-28432-1-git-send-email-ville.syrjala@linux.intel.com>
	<m2zjyww1c5.fsf@firstfloor.org>
Mime-Version: 1.0
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
Return-path: <intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org>
Received: from mga02.intel.com (mga02.intel.com [134.134.136.20])
	by gabe.freedesktop.org (Postfix) with ESMTP id 0713EE631E
	for <intel-gfx@lists.freedesktop.org>;
	Mon, 25 Feb 2013 02:58:04 -0800 (PST)
Content-Disposition: inline
In-Reply-To: <m2zjyww1c5.fsf@firstfloor.org>
List-Unsubscribe: <http://lists.freedesktop.org/mailman/options/intel-gfx>,
	<mailto:intel-gfx-request@lists.freedesktop.org?subject=unsubscribe>
List-Archive: <http://lists.freedesktop.org/archives/intel-gfx>
List-Post: <mailto:intel-gfx@lists.freedesktop.org>
List-Help: <mailto:intel-gfx-request@lists.freedesktop.org?subject=help>
List-Subscribe: <http://lists.freedesktop.org/mailman/listinfo/intel-gfx>,
	<mailto:intel-gfx-request@lists.freedesktop.org?subject=subscribe>
Sender: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org
Errors-To: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org
To: Andi Kleen <andi@firstfloor.org>
Cc: intel-gfx@lists.freedesktop.org
List-Id: intel-gfx@lists.freedesktop.org

On Fri, Feb 22, 2013 at 12:16:58PM -0800, Andi Kleen wrote:
> ville.syrjala@linux.intel.com writes:
> =

> > From: Ville Syrj=E4l=E4 <ville.syrjala@linux.intel.com>
> >
> > to_user_ptr() simply casts a pointer passed as u64 from user space
> > to void __user * correctly. Using this lets us get rid of all the
> > tiresome casts.
> =

> The whole point of __user is to track it elsewhere to avoid mistakes,
> which may result in security bugs.
> =

> A __user cast usually means your tracking is not complete, it's
> supposed to be ugly so that you fix the tracking. Prettying
> it defeats that point.
> =

> How about just changing the original field to a pointer and add
> the __user there?

That would introduce 32bit vs. 64bit issues. We pass all user space
pointer as __u64 precisely to avoid such issues.

-- =

Ville Syrj=E4l=E4
Intel OTC