From owner-freebsd-hackers  Tue Jul 29 20:32:58 1997
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To: Michael Smith <msmith@atrad.adelaide.edu.au>
cc: freebsd-hackers@FreeBSD.ORG
Subject: Re: Location of copyin() and copyout().. 
In-reply-to: Your message of "Wed, 30 Jul 1997 12:52:18 +0930."
             <199707300322.MAA17715@genesis.atrad.adelaide.edu.au> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Tue, 29 Jul 1997 20:33:55 -0700
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>So, I write a function linux_i386_modify_ldt(), which lives in the
>linux emulation module.  It takes the Linux i386_modify_ldt() syscall,
>converts the arguments to the right format, and tries to call
>i386_set_ldt().
>
>Only it _can't_, because the latter is using copyin(), and cannot access
>the argument structure in kernel space.

   Ah, now I understand. Yes, copyin/out do page protection checking and will
not allow a copyout to kernel memory or a copyin from kernel memory (since
kernel memory is protected against users).

-DG

David Greenman
Core-team/Principal Architect, The FreeBSD Project