port-amd64/52896: amd64 kernel seems to have RWX mappings

[coypu%sdf.org@localhost]

>Number:         52896
>Category:       port-amd64
>Synopsis:       amd64 kernel seems to have RWX mappings
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    port-amd64-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Jan 03 22:30:00 +0000 2018
>Originator:     coypu
>Release:        NetBSD 8.99.9
>Organization:
>Environment:
NetBSD localhost 8.99.9 NetBSD 8.99.9 (GENERIC) #9: Sat Dec  9 18:35:18 IST 2017  fly@localhost:/home/fly/obj/sys/arch/amd64/compile/GENERIC amd64

>Description:
# pmap 0
(omitting non RWX mappings)
FFFF800000000000 471856K read/write/exec     [ anon ]
FFFF80001CCCC000 4150224K read/write/exec     [ anon ]
FFFF80011A1C0000 524288K read/write/exec     [ pager_map ]
FFFF80013A1DA000   1200K read/write/exec     [ phys_map ]
FFFF80013EEA9000   8192K read/write/exec     [ ubc_pager ]
FFFF80013F6AD000   4096K read/write/exec     [ exec_map ]

it's possible pmap (the program) is wrong, but it seems like any executable mapping is also writable.
>How-To-Repeat:

>Fix: