Re: Generic DMA - BUG_ON

From: Russell King
Date: Thu Jan 21 2010 - 12:54:11 EST

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
> > > 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 -
maintainer of:
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