Asked ASRock about mitigation of Spectre for my ASRock X370 AMD motherboard and this the response I received
18 January 2018 at 04:30 (+11UTC)
___________________

Hi Roy,

Please refer to the AMD’s announcement from following link.
https://www.amd.com/en/corporate/speculative-execution
The customer needs to software/OS update.
It does not affect the BIOS of the AMD motherboard.

Thank you

ASRock America Support Team
__________________

WTF ASRock?