Date: Sat, 3 Dec 2005 10:43:14 +0100
From: Heiko Carstens <heiko.carstens@de.ibm.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Al Viro <viro@ftp.linux.org.uk>,
       Vinay Venkataraghavan <raghavanvinay@yahoo.com>,
       linux-kernel@vger.kernel.org
Subject: Re: copy_from_user/copy_to_user question
Message-ID: <20051203094314.GB8135@osiris.boeblingen.de.ibm.com>
References: <20051202224025.39396.qmail@web32108.mail.mud.yahoo.com> <1133572199.32583.93.camel@localhost.localdomain> <20051203013833.GG27946@ftp.linux.org.uk> <1133575346.4894.7.camel@localhost.localdomain>
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> > > > 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.

Heiko
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