Subject: Re: copy_from_user/copy_to_user question
From: Steven Rostedt <rostedt@goodmis.org>
To: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Al Viro <viro@ftp.linux.org.uk>,
       Vinay Venkataraghavan <raghavanvinay@yahoo.com>,
       linux-kernel@vger.kernel.org
In-Reply-To: <20051203094314.GB8135@osiris.boeblingen.de.ibm.com>
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Date: Sat, 03 Dec 2005 07:14:45 -0500
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On Sat, 2005-12-03 at 10:43 +0100, Heiko Carstens wrote:
> > > > > Secondly, they seem to use memcpy as opposed to using
> > > > > copy_to_user/copy_from_user which is also very
> > > > > dangerous.
> > > > 
> > > > If they are grabbing data from user context into kernel (or vise versa)
> > > > that could easily cause an oops.  Not to mention it is a security risk.
> > > 
> > > Not to mention it simply won't work on a many platforms, no matter what...
> > 
> > Hmm, I've only worked with a few platforms (i386, x86_64, ppc, mips, and
> > a little arm but I don't remember that much).  I believe that a memcpy
> > could work on all these platforms (error prone of course, but if the
> > memory is mapped its OK).  When entering a system call, the kernel still
> > has access to the memory locations assigned to the user.
> 
> Won't work at all on platforms that have distinct address spaces for user
> and kernel space. E.g. on s390/s390x it wouldn't work. And yes, there are
> special instructions to copy data between address spaces.

Thanks for the update.  That's why I love working in an open
environment.  You learn something new every day ;)

-- Steve


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