kern/58087: hyperv provides random seed

[campbell+netbsd%mumble.net@localhost]

>Number:         58087
>Category:       kern
>Synopsis:       hyperv provides random seed
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Mar 29 01:55:00 +0000 2024
>Originator:     Taylor R Campbell
>Release:        current
>Organization:
The NetBSD-V Foundation
>Environment:
>Description:
According to Niels Ferguson, `The Windows 10 random number generation
infrastructure', October 2019, Hyper-V provides an ACPI table called
`OEM0' with a random seed (p. 14):

> * ACPI-OEM0
> 
> The ACPI-OEM0 is an ACPI table with the name OEM0.  The Hyper-V
> hypervisor will create this table with 64 bytes of random data.  The
> random data is derived from the host RNG infrastructure, and a fresh
> value is passed every time a guest is powered up.  OEMs could provide
> this table on physical machines too, but we are not aware of any OEM
> doing that.  The ACPI-OEM0 table is read by winload.  It ensures that
> any VM guest on Hyper-V has good entropy at startup.  (This is
> especially important as many VMs are often launched from the same
> disk image, so they all get the same seedfile data.)

https://download.microsoft.com/download/1/c/9/1c9813b8-089c-4fef-b2ad-ad80e79403ba/Whitepaper%20-%20The%20Windows%2010%20random%20number%20generation%20infrastructure.pdf

We should take advantage of this in NetBSD when booting on
Hyper-V (and make sure to zero it out when exposing the table
through /dev/acpi).
>How-To-Repeat:
boot NetBSD on hyperv
>Fix:
Yes, please!