Subject: /dev/mem and kernel security
To: None <amiga@NetBSD.ORG>
From: David Jones <dej@eecg.toronto.edu>
List: amiga
Date: 02/10/1995 15:46:08 
> I have been trying to talk to a board using the /dev/mem interface.
> However, when I open with O_RDWR, it fails with EPERM.  I have tested 

I believe 4.4_Lite has the concept of "kernel security levels".  At level 1,
writes to /dev/mem and /dev/kmem are denied, even to root.  This stops the
"binpatch the kernel" type cracks.