prevent breaking a chroot() jail?

[Shaya Potter <spotter@cs.columbia.edu>]

I'm trying to develop a way to ensure that one can't break out of a
chroot() jail, even as root.  I'm willing to change the way the syscalls
work (most likely only for a subset of processes, i.e. processes that
are run in the jail end up getting a marker which is passed down to all
their children that causes the syscalls to behave differently).

What should I be aware of?  I figure devices (no need to run mknod in
this jail) and chroot (as per man page), is there any other way of
breaking the chroot jail (at a syscall level or otherwise)?

or is this 100% impossible?

thanks,

shaya