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Date: Fri, 17 Oct 2003 15:50:28 -0700
From: Andrew Morton <akpm@osdl.org>
To: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC] prevent "dd if=/dev/mem" crash
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Bjorn Helgaas <bjorn.helgaas@hp.com> wrote:
>
> Old behavior:
> 
>     # dd if=/dev/mem of=/dev/null
>     <unrecoverable machine check>

I recently fixed this for ia32 by changing copy_to_user() to not oops if
the source address generated a fault.  Similarly copy_from_user() returns
an error if the destination generates a fault.

In other words: drivers/char/mem.c requires that the architecture's
copy_*_user() functions correctly handle faults on either the source or
dest of the copy.