linux-kernel - Re: Generic DMA

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Message-ID: <20100121175317.GA14752@flint.arm.linux.org.uk>
Date:	Thu, 21 Jan 2010 17:53:17 +0000
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	"Steven J. Magnani" <steve@...idescorp.com>
Cc:	Joerg Roedel <joerg.roedel@....com>, monstr@...str.eu,
	linux-kernel@...r.kernel.org, michal.simek@...alogix.com,
	arnd@...db.de, linux-arch@...r.kernel.org,
	fujita.tomonori@....ntt.co.jp, akpm@...ux-foundation.org,
	mingo@...e.hu
Subject: Re: Generic DMA - BUG_ON

On Thu, Jan 21, 2010 at 09:51:37AM -0600, Steven J. Magnani wrote:
> On Wed, 2010-01-20 at 12:00 +0100, Joerg Roedel wrote:
> > On Wed, Jan 20, 2010 at 10:53:50AM +0000, Russell King wrote:
> > > and ops is NULL, then this code will oops; you will get a full register
> > > dump and backtrace.  You can use this information along with markup_oops.pl
> > > to find out where the problem is.
> > 
> > You can't rely on the oops if the code runs in process context. The
> > process may have address 0 mapped which would result in a security hole.
> > We had two of these bugs last year.
> 
> You also can't rely on an oops in a NOMMU environment.

I don't see why implementations where NULL pointer derefs should be
penalized by having additional NULL checks.

Maybe this needs to be a conditional check which can be optimized away
on architectures where NULL dereference always produces an oops.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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