I have Fedora Workstation 42 on a laptop, with untrusted libvirt-managed virtual machines.

I would like to secure the host from the virtual machines, and ensure they are unable to interact with each other.

My system uses SELinux in its default configuration. The output of sestatus:

SELinux status:                 enabled
SELinuxfs mount:                /sys/fs/selinux
SELinux root directory:         /etc/selinux
Loaded policy name:             targeted
Current mode:                   enforcing
Mode from config file:          enforcing
Policy MLS status:              enabled
Policy deny_unknown status:     allowed
Memory protection checking:     actual (secure)
Max kernel policy version:      35

and the output of getsebool -a is as follows:

abrt_anon_write --> off
abrt_handle_event --> on
abrt_upload_watch_anon_write --> on
antivirus_can_scan_system --> off
antivirus_use_jit --> off
auditadm_exec_content --> on
authlogin_nsswitch_use_ldap --> off
authlogin_radius --> off
authlogin_yubikey --> off
awstats_purge_apache_log_files --> off
boinc_execmem --> on
cdrecord_read_content --> off
cluster_can_network_connect --> off
cluster_manage_all_files --> off
cluster_use_execmem --> off
cobbler_anon_write --> off
cobbler_can_network_connect --> off
cobbler_use_cifs --> off
cobbler_use_nfs --> off
collectd_tcp_network_connect --> off
colord_use_nfs --> off
condor_tcp_network_connect --> off
conman_can_network --> off
conman_use_nfs --> off
container_connect_any --> off
container_manage_cgroup --> off
container_modify_selinux_labels --> off
container_read_certs --> off
container_use_cephfs --> off
container_use_devices --> off
container_use_dri_devices --> on
container_use_ecryptfs --> off
container_use_xserver_devices --> off
container_user_exec_content --> on
cron_can_relabel --> off
cron_system_cronjob_use_shares --> off
cron_userdomain_transition --> on
cups_execmem --> off
cvs_read_shadow --> off
daemons_dontaudit_scheduling --> on
daemons_dump_core --> off
daemons_enable_cluster_mode --> off
daemons_use_tcp_wrapper --> off
daemons_use_tty --> off
dbadm_exec_content --> on
dbadm_manage_user_files --> off
dbadm_read_user_files --> off
deny_bluetooth --> off
deny_execmem --> off
deny_ptrace --> off
dhcpc_exec_iptables --> off
dhcpd_use_ldap --> off
dnsmasq_use_ipset --> off
domain_can_mmap_files --> off
domain_can_write_kmsg --> off
domain_fd_use --> on
domain_kernel_load_modules --> on
entropyd_use_audio --> on
exim_can_connect_db --> off
exim_manage_user_files --> off
exim_read_user_files --> off
fcron_crond --> off
fenced_can_network_connect --> off
fenced_can_ssh --> off
fips_mode --> on
ftpd_anon_write --> off
ftpd_connect_all_unreserved --> off
ftpd_connect_db --> off
ftpd_full_access --> off
ftpd_use_cifs --> off
ftpd_use_fusefs --> off
ftpd_use_nfs --> off
ftpd_use_passive_mode --> off
git_cgi_enable_homedirs --> off
git_cgi_use_cifs --> off
git_cgi_use_nfs --> off
git_session_bind_all_unreserved_ports --> off
git_session_users --> off
git_system_enable_homedirs --> off
git_system_use_cifs --> off
git_system_use_nfs --> off
gitosis_can_sendmail --> off
glance_api_can_network --> off
glance_use_execmem --> off
glance_use_fusefs --> off
global_ssp --> off
gluster_anon_write --> off
gluster_export_all_ro --> off
gluster_export_all_rw --> on
gluster_use_execmem --> off
gpg_web_anon_write --> off
gssd_read_tmp --> on
guest_exec_content --> on
haproxy_connect_any --> off
httpd_anon_write --> off
httpd_builtin_scripting --> on
httpd_can_check_spam --> off
httpd_can_connect_ftp --> off
httpd_can_connect_ldap --> off
httpd_can_connect_mythtv --> off
httpd_can_connect_zabbix --> off
httpd_can_manage_courier_spool --> off
httpd_can_network_connect --> off
httpd_can_network_connect_cobbler --> off
httpd_can_network_connect_db --> off
httpd_can_network_memcache --> off
httpd_can_network_redis --> off
httpd_can_network_relay --> off
httpd_can_sendmail --> off
httpd_dbus_avahi --> off
httpd_dbus_sssd --> off
httpd_dontaudit_search_dirs --> off
httpd_enable_cgi --> on
httpd_enable_ftp_server --> off
httpd_enable_homedirs --> off
httpd_execmem --> off
httpd_graceful_shutdown --> off
httpd_manage_ipa --> off
httpd_mod_auth_ntlm_winbind --> off
httpd_mod_auth_pam --> off
httpd_read_user_content --> off
httpd_run_ipa --> off
httpd_run_preupgrade --> off
httpd_run_stickshift --> off
httpd_serve_cobbler_files --> off
httpd_setrlimit --> off
httpd_ssi_exec --> off
httpd_sys_script_anon_write --> off
httpd_tmp_exec --> off
httpd_tty_comm --> off
httpd_unified --> off
httpd_use_cifs --> off
httpd_use_fusefs --> off
httpd_use_gpg --> off
httpd_use_nfs --> off
httpd_use_opencryptoki --> off
httpd_use_openstack --> off
httpd_use_sasl --> off
httpd_verify_dns --> off
icecast_use_any_tcp_ports --> off
init_audit_control --> on
init_create_dirs --> on
irc_use_any_tcp_ports --> off
irqbalance_run_unconfined --> off
irssi_use_full_network --> off
kdumpgui_run_bootloader --> off
keepalived_connect_any --> off
kerberos_enabled --> on
ksmtuned_use_cifs --> off
ksmtuned_use_nfs --> off
logadm_exec_content --> on
logging_syslogd_append_public_content --> off
logging_syslogd_can_sendmail --> off
logging_syslogd_list_non_security_dirs --> off
logging_syslogd_run_nagios_plugins --> off
logging_syslogd_run_unconfined --> off
logging_syslogd_use_tty --> on
login_console_enabled --> on
logrotate_read_inside_containers --> off
logrotate_use_cifs --> off
logrotate_use_fusefs --> off
logrotate_use_nfs --> off
logwatch_can_network_connect_mail --> off
lsmd_plugin_connect_any --> off
mailman_use_fusefs --> off
mcelog_client --> off
mcelog_exec_scripts --> on
mcelog_foreground --> off
mcelog_server --> off
minidlna_read_generic_user_content --> off
mmap_low_allowed --> off
mock_enable_homedirs --> off
mount_anyfile --> on
mozilla_plugin_bind_unreserved_ports --> off
mozilla_plugin_can_network_connect --> on
mozilla_plugin_use_bluejeans --> off
mozilla_plugin_use_gps --> off
mozilla_plugin_use_spice --> off
mozilla_read_content --> off
mpd_enable_homedirs --> off
mpd_use_cifs --> off
mpd_use_nfs --> off
mplayer_execstack --> off
mysql_connect_any --> off
mysql_connect_http --> off
nagios_run_pnp4nagios --> off
nagios_run_sudo --> off
nagios_use_nfs --> off
named_tcp_bind_http_port --> off
named_write_master_zones --> on
neutron_can_network --> off
nfs_export_all_ro --> on
nfs_export_all_rw --> on
nfsd_anon_write --> off
nis_enabled --> off
nscd_use_shm --> on
openfortivpn_can_network_connect --> on
openshift_use_nfs --> off
openvpn_can_network_connect --> on
openvpn_enable_homedirs --> on
openvpn_run_unconfined --> off
pasta_bind_all_ports --> on
pdns_can_network_connect_db --> off
polipo_connect_all_unreserved --> off
polipo_session_bind_all_unreserved_ports --> off
polipo_session_users --> off
polipo_use_cifs --> off
polipo_use_nfs --> off
polyinstantiation_enabled --> off
postfix_local_write_mail_spool --> on
postgresql_can_rsync --> off
postgresql_selinux_transmit_client_label --> off
postgresql_selinux_unconfined_dbadm --> on
postgresql_selinux_users_ddl --> on
pppd_can_insmod --> off
pppd_for_user --> off
privoxy_connect_any --> on
prosody_bind_http_port --> off
puppetagent_manage_all_files --> off
puppetmaster_use_db --> off
racoon_read_shadow --> off
radius_use_jit --> off
redis_enable_notify --> off
rngd_execmem --> off
rpcd_use_fusefs --> off
rsync_anon_write --> off
rsync_client --> off
rsync_export_all_ro --> off
rsync_full_access --> off
rsync_sys_admin --> off
samba_create_home_dirs --> off
samba_domain_controller --> off
samba_enable_home_dirs --> off
samba_export_all_ro --> off
samba_export_all_rw --> off
samba_load_libgfapi --> off
samba_portmapper --> off
samba_run_unconfined --> off
samba_share_fusefs --> off
samba_share_nfs --> off
sanlock_enable_home_dirs --> off
sanlock_use_fusefs --> off
sanlock_use_nfs --> off
sanlock_use_samba --> off
saslauthd_read_shadow --> off
screen_allow_session_sharing --> off
secadm_exec_content --> on
secure_mode --> off
secure_mode_insmod --> off
secure_mode_policyload --> off
selinuxuser_direct_dri_enabled --> on
selinuxuser_execheap --> off
selinuxuser_execmod --> on
selinuxuser_execstack --> on
selinuxuser_mysql_connect_enabled --> off
selinuxuser_ping --> on
selinuxuser_postgresql_connect_enabled --> off
selinuxuser_rw_noexattrfile --> on
selinuxuser_share_music --> off
selinuxuser_tcp_server --> off
selinuxuser_udp_server --> off
selinuxuser_use_ssh_chroot --> off
smartmon_3ware --> off
smbd_anon_write --> off
spamassassin_can_network --> off
spamd_enable_home_dirs --> on
spamd_update_can_network --> off
squid_bind_snmp_port --> off
squid_connect_any --> on
squid_use_tproxy --> off
ssh_chroot_rw_homedirs --> off
ssh_keysign --> off
ssh_sysadm_login --> off
ssh_use_tcpd --> off
sshd_launch_containers --> off
sslh_can_bind_any_port --> off
sslh_can_connect_any_port --> off
sssd_access_kernel_keys --> off
sssd_connect_all_unreserved_ports --> off
sssd_use_usb --> off
staff_exec_content --> on
staff_use_svirt --> off
swift_can_network --> off
sysadm_exec_content --> on
systemd_socket_proxyd_bind_any --> off
systemd_socket_proxyd_connect_any --> off
telepathy_connect_all_ports --> off
telepathy_tcp_connect_generic_network_ports --> on
tftp_anon_write --> off
tftp_home_dir --> off
tmpreaper_use_cifs --> off
tmpreaper_use_nfs --> off
tmpreaper_use_samba --> off
tomcat_can_network_connect_db --> off
tomcat_read_rpm_db --> off
tomcat_use_execmem --> off
tor_bind_all_unreserved_ports --> off
tor_can_network_relay --> off
tor_can_onion_services --> off
unconfined_chrome_sandbox_transition --> on
unconfined_dyntrans_all --> off
unconfined_login --> on
unconfined_mozilla_plugin_transition --> on
unprivuser_use_svirt --> off
use_ecryptfs_home_dirs --> off
use_fusefs_home_dirs --> off
use_lpd_server --> off
use_nfs_home_dirs --> off
use_samba_home_dirs --> off
use_virtualbox --> on
user_exec_content --> on
varnishd_connect_any --> off
virt_hooks_unconfined --> off
virt_lockd_blk_devs --> off
virt_qemu_ga_manage_ssh --> off
virt_qemu_ga_read_nonsecurity_files --> off
virt_qemu_ga_run_unconfined --> off
virt_read_qemu_ga_data --> off
virt_rw_qemu_ga_data --> off
virt_sandbox_share_apache_content --> off
virt_sandbox_use_all_caps --> on
virt_sandbox_use_audit --> on
virt_sandbox_use_fusefs --> off
virt_sandbox_use_mknod --> off
virt_sandbox_use_netlink --> off
virt_sandbox_use_sys_admin --> off
virt_transition_userdomain --> off
virt_use_comm --> off
virt_use_execmem --> off
virt_use_fusefs --> off
virt_use_glusterd --> off
virt_use_nfs --> on
virt_use_pcscd --> off
virt_use_pulseaudio --> off
virt_use_rawip --> off
virt_use_samba --> off
virt_use_sanlock --> off
virt_use_usb --> on
virt_use_xserver --> off
virtqemud_use_execmem --> on
webadm_manage_user_files --> off
webadm_read_user_files --> off
wine_mmap_zero_ignore --> off
xdm_bind_vnc_tcp_port --> off
xdm_exec_bootloader --> off
xdm_manage_bootloader --> on
xdm_sysadm_login --> off
xdm_write_home --> off
xen_use_nfs --> off
xend_run_blktap --> on
xend_run_qemu --> on
xenstored_use_store_type_domain --> off
xguest_connect_network --> on
xguest_exec_content --> on
xguest_mount_media --> on
xguest_use_bluetooth --> on
xserver_clients_write_xshm --> off
xserver_execmem --> off
xserver_object_manager --> off
zabbix_can_network --> off
zabbix_run_sudo --> off
zarafa_setrlimit --> off
zebra_write_config --> off
zoneminder_anon_write --> off
zoneminder_run_sudo --> off

When I first launched libvirt, a new network was created, and a new zone showed up in the output of firewall-cmd --get-active-zones:

FedoraWorkstation (default)
  interfaces: wlp0s20f3
libvirt
  interfaces: virbr0

I inspected the configuration of this zone, firewall-cmd --permanent --info-zone libvirt, and some services, including ssh and tftp, are listed after services:. I made sure to remove what seemed extraneous to me, and right now my permanent configuration is:

firewall-cmd --permanent --info-zone libvirt
libvirt
  target: ACCEPT
  ingress-priority: 0
  egress-priority: 0
  icmp-block-inversion: no
  interfaces:
  sources:
  services: dhcp dhcpv6 dns
  ports:
  protocols: icmp ipv6-icmp
  forward: no
  masquerade: no
  forward-ports:
  source-ports:
  icmp-blocks:
  rich rules:
    rule priority="32767" reject

and non-permanent configuration (firewall-cmd --info-zone libvirt) looks like this:

  target: ACCEPT
  ingress-priority: 0
  egress-priority: 0
  icmp-block-inversion: no
  interfaces: virbr0
  sources:
  services: dhcp dhcpv6 dns
  ports:
  protocols: icmp ipv6-icmp
  forward: no
  masquerade: no
  forward-ports:
  source-ports:
  icmp-blocks:
  rich rules:
    rule priority="32767" reject

When I create new untrusted libvirt domains, I make sure to add:

<clipboard copypaste="no"/>
<filetransfer enable="no"/>

to the configuration of "Display Spice" in virt-manager, and remove all virtual devices that aren't used, such as USB redirectors and sound cards. I also install the domains with /usr/share/edk2/ovmf/OVMF_CODE_4M.secboot.qcow2 firmware, though I am not sure if the domain running in UEFI SecureBoot mode affects anything. I would greatly appreciate advice here.

What else can I do to secure the host system from untrusted virtual machines?

In addition, I would like to secure them from each other.

As of right now, I manually configure FirewallD inside every such machine to only allow connections from host, but this doesn't really scale, so I would appreciate advice on how to configure this on the host's side.

Thank you!