kern/53599: Can't enter ddb using USB keyboard because console

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         53599
>Category:       kern
>Synopsis:       Can't enter ddb using USB keyboard because console
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Sep 12 13:05:00 +0000 2018
>Originator:     Andreas Gustafsson
>Release:        NetBSD 8.0
>Organization:
>Environment:
System: NetBSD
Architecture: x86_64
Machine: amd64
>Description:

When I plug a USB keyboard into a USB port on a HP DL360 G7 running a
GENERIC kernel from the NetBSD/amd64 8.0 release and hit ctrl-alt-esc,
nothing happens.

Apparently this is because the call to console_debugger() in wskbd.c
is inside "if (sc->sc_isconsole)", and sc_isconsole is false.  The
dmesg says:

  pckbd0 at pckbc1 (kbd slot)
  pckbc1: using irq 1 for kbd slot
  wskbd0 at pckbd0: console keyboard
  [...]
  uhidev0 at uhub0 port 1 configuration 1 interface 0
  uhidev0: HP (0x3f0) Virtual Keyboard (0x7029), rev 1.10/0.02, addr 2, iclass 3/1
  ukbd0 at uhidev0
  wskbd1 at ukbd0 mux 1
  wskbd1: connecting to wsdisplay0
  [...]
  uhidev2 at uhub3 port 1 configuration 1 interface 0
  uhidev2: Hewlett-Packard Company (0x3f0) HP USB Smart Card Keyboard (0x1024), rev 2.00/5.35, addr 2, iclass 3/1
  ukbd1 at uhidev2
  wskbd2 at ukbd1 mux 1
  wskbd2: connecting to wsdisplay0

The machine does not have a PS/2 keyboard connector.  The keyboard I
plugged in and tried to enter ddb from is the one attached as wskbd2.

I realize that there is a tradeoff between security and debuggability
here, but at least there should be a simple and documented way to
configure the system to allow ddb to be entered from any USB keyboard
without having to build a custom kernel.  If there already is one,
please enlighten me...

>How-To-Repeat:

>Fix: