Description of problem:
The following command line should validate a SEV guest, overriding the CPU model/stepping/family that are otherwise extracted from libvirt.

1. virt-qemu-sev-validate --tik sev_es_dhcert_tik.bin --tek sev_es_dhcert_tek.bin --domain berrange --insecure --debug --cpu-model 1 --cpu-family 25 --cpu-stepping 1
   [DEBUG]: TIK(hex): 5802c018ba97b67cffb6e4634e613727
   [DEBUG]: TEK(hex): 5e766810c034d98345946884483198f0
   File "/usr/bin/virt-qemu-sev-validate", line 1301, in main
   attest(args)
   File "/usr/bin/virt-qemu-sev-validate", line 1262, in attest
   cvm.build_vmsas(args.cpu_family,
   File "/usr/bin/virt-qemu-sev-validate", line 713, in build_vmsas
   ovmf.load(self.firmware)
   File "/usr/bin/virt-qemu-sev-validate", line 469, in load
   actual = content[-48:-32]
   ERROR: 'NoneType' object is not subscriptable

The failure is because when --cpu-family/model/stepping args are provided in combination with --domain, we try to build the VMSA before we've acquired the firmware.

Adding --firmware to the above args is a workaround

1. virt-qemu-sev-validate --tik sev_es_dhcert_tik.bin --tek sev_es_dhcert_tek.bin --domain berrange --insecure --debug --cpu-model 1 --cpu-family 25 --cpu-stepping 1 --firmware /usr/share/edk2/ovmf/OVMF.amdsev.fd
   [DEBUG]: Firmware(sha256): 906a0dcb21704b36758493a7e29b6f4102f50fd0dd800a04742c0f69f3ed6e19
   [DEBUG]: TIK(hex): 5802c018ba97b67cffb6e4634e613727
   [DEBUG]: TEK(hex): 5e766810c034d98345946884483198f0
   [DEBUG]: VMSA CPU 0(sha256): f8b52f775502472e5797d2674d9de21f6abc05dc05e9bc49cbb7b6a13688d5e7
   [DEBUG]: VMSA CPU 1(sha256): bcee5cb289f72882da17abd8dca5e8a7e9f8e2033e7ad96b4db0ab1a383a6487
   [DEBUG]: VM: id=1 name=berrange uuid=99999999-7f0d-44c3-abee-eb1424bb23e7
   [DEBUG]: VMSA(sha256): 0e5246de248812527b171d60d6851f37875ac4b22063f73f4e56d0dc4546d192
   [DEBUG]: Measured-data(sha256): 4a470ecd611f292e0e168828688c9d24539a05131a96ce092397a74c1cbad0d2
   [DEBUG]: Measured-msg(hex): 04013705070000004a470ecd611f292e0e168828688c9d24539a05131a96ce092397a74c1cbad0d2233e47003f79b80fa1177bfe04195f92
   [DEBUG]: Measurement reported(hex): aa0b21bb54bab669025cdefa744c2026ccdae77e9ac25196e0530bb7eb84b353
   [DEBUG]: Measurement computed(hex): aa0b21bb54bab669025cdefa744c2026ccdae77e9ac25196e0530bb7eb84b353
   OK: Looks good to me

Version-Release number of selected component (if applicable):
libvirt-client-qemu-9.5.0-5.el9.x86_64

How reproducible:
Always

Steps to Reproduce:
1. Use virt-qemu-sev-validate with --domain and --cpu-family/model/stepping, and WITHOUT --firmware

Actual results:
Exception trace

Expected results:
Validates guest

Additional info: