linux-kernel - Re: [RFC PATCH 02/12] On Tue, 23 Sep 2008, David Miller wrote:

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Message-ID: <20081005100117.2277d70c@linux.intel.com>
Date:	Sun, 5 Oct 2008 10:01:17 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Jesse Brandeburg <jesse.brandeburg@...il.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	David Miller <davem@...emloft.net>, jesse.brandeburg@...el.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	kkeil@...e.de, agospoda@...hat.com, david.graham@...el.com,
	bruce.w.allan@...el.com, john.ronciak@...el.com,
	chris.jones@...onical.com, tim.gardner@...onical.com,
	airlied@...il.com, Olaf Kirch <okir@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC PATCH 02/12] On Tue, 23 Sep 2008, David Miller wrote:

On Sun, 5 Oct 2008 18:16:29 +0200 (CEST)
Thomas Gleixner <tglx@...utronix.de> wrote:

> On Sun, 5 Oct 2008, Arjan van de Ven wrote:
> > On Sun, 5 Oct 2008 17:55:14 +0200 (CEST)
> > Thomas Gleixner <tglx@...utronix.de> wrote:
> > 
> > > On Sun, 5 Oct 2008, Arjan van de Ven wrote:
> > > > Thomas Gleixner wrote:
> > > > > On Sat, 4 Oct 2008, Jesse Brandeburg wrote:
> > > > > > > Exactly. The access to a ro region results in a fault. I
> > > > > > > have nowhere seen that trigger, but I can reproduce the
> > > > > > > trylock() WARN_ON, which confirms that there is
> > > > > > > concurrent access to the NVRAM registers. The backtrace
> > > > > > > pattern is similar to the one you have seen.
> > > > > > are you still getting WARN_ON *with* all the mutex based
> > > > > > fixes already applied?
> > > > > 
> > > > > The WARN_ON triggers with current mainline. Is there any
> > > > > fixlet in Linus tree missing ?
> > > > > 
> > > > > > with the mutex patches in place (without protection patch)
> > > > > > we are still reproducing the issue, until we apply the
> > > > > > set_memory_ro patch.
> > > > > 
> > > > > That does not make sense to me. If the memory_ro patch is
> > > > > providing _real_ protection then you _must_ run into an access
> > > > > violation. If not, then the patch just papers over the real
> > > > > problem in some mysterious way.
> > > > > 
> > > > 
> > > > not if the bad code is doing copy_to_user .... (or similar)
> > > 
> > > You mean: copy_from_user :) This would require that the e1000e
> > > nvram region is writable via copy_from_user by an e1000e user
> > > space interface. A quick grep does not reviel such a horrible
> > > interface.
> > 
> > I meant a "copy_to_user" to a duff pointer, somewhere in the kernel.
> 
> Hmm, don't we check the *to address on copy_to_user ?
> 

fair point

and we do exception catching for copy_from_user as well on the source,
just by how it's implemented

-- 
Arjan van de Ven 	Intel Open Source Technology Centre
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