We sometimes store sensitive things in the kenv that get zapped, but we
really shouldn't rely on that zapping to actually happen. Most
unprivileged processes don't really need to read from the kernel
environment in the first place, so add a knob that allows it to be
disabled.
Note that we consider jailed root to be unprivileged from this
perspective; they have their own meta/env concepts and we should
encourage users to take advantage of those for passing information to
jails.
Relnotes: yes (The capability to disable unpriv access exists)
"Hey we should do something about that": dch
Reviewed by: imp, ziaee, zlei (all slightly previous version)
Differential Revision: https://reviews.freebsd.org/D57697
(cherry picked from commit 4fd518fcb2)
Kyle Evans
c839c15661