It's the one distributed with the engine: /usr/share/virtio-win/virtio-win-1.9.16.iso
"2. Virtio-win licence:
This License Agreement ("License") applies to the VirtIO paravirtualized
drivers for Windows(R) ("virtio-win") software ("Program") and any
related
updates or patches to the Program regardless of how you ("User") obtain
such updates or patches.
1. Intellectual Property Rights. The Program is owned by Red Hat and others
and is protected under copyright and other laws. Title to the Program or to
any copy, modification, or merged portion shall remain with the
aforementioned.
The "Red Hat" trademark and the "Shadowman" logo are registered
trademarks of
Red Hat in the U.S. and other countries.
2. Program License Grant. Red Hat grants User a non-exclusive,
non-transferable license to use the Program during the term of and on systems
with fully-paid applicable Red Hat subscription(s) provided User may not:
(a) modify, copy, or create any derivative works of the Program;
(b) decompile, disassemble or reverse engineer the Program (except to the
extent permitted by applicable law);
(c) redistribute, encumber, sell, rent, lease, sublicense, or otherwise
transfer rights to the Program (except to the extent permitted herein); or
(d) remove or alter any trademark, logo, copyright or other proprietary
notices, legends, symbols or labels in the Program. Upon expiration of the
term set forth above, User will promptly remove, delete or destroy all copies
of the Program in its possession."