Prodesk 600 G4 BIOS is locked from downgrading BIOS version

[danwat123]

I have a number of Prodesk 600 G4 Prodesk boxes with an i5-8500 CPU. Upon running the Windows-based  BIOS updater to downgrade  to version 2.02 from 2.2 or so, it reboots to start the process. It fails. "BIOS Update did not proceed because the system administrator has locked the BIOS version. Next screen upon fail; "BIOS pudate denied by system policy. Cancelling the system BIOS update. 

I have tried removing CMOS battery, removing BIOS password jumper (even though that is not the issue), the yello button on the motherboard.. What is the solution? it is not the data on the SSD it is a new blank drive. Is there a way to remove this protection? I need to downgrade in order to enable CPU undervolting to increase efficiency.

[DGroves]

when hp prevents a bios downgrade there is usually a very good reason for this ranging from severe security flaws in older revisions to bios structure incompatibility between old/new bios and so on

in your case HP plainly states on their bios 02.27.00 Rev.A page for your system:

NOTE: Due to HP Sure Admin feature support, system is not compatible with 02.12.00 or older BIOS version once it is enabled, attempts to install older BIOS versions will be blocked.

This BIOS upgrade package also includes the following firmware versions:
EC/SIO F/W 7.9.52
Cypress PD FW (CCG5) 6.8.0
Intel Legacy VBIOS 9.2.1014
Intel GOP EFI Driver 9.0.1075
GbE Version 0054 (I219LM)
PXE option ROM 0.1.13
PXE UEFI Driver 0.0.19
ME Firmware Corporate v12.0.94.2380 (Production)

- Updates Intel MCU for compatibility enhancement
- Enhancement to address security vulnerabilities CVE-2023-28389, CVE-2023-27502 and CVE-2023-32633

please explain just why you think a older bios will give you something useable that a newer one will not i find no differences between bios versions related to undervolting

https://support.hp.com/nz-en/drivers/hp-prodesk-600-g4-small-form-factor-pc/21341193

[danwat123]

Needs to be newer than 2.12, so I downloaded 2.14 (there is no 2.13 here https://support.hp.com/nz-en/drivers/swdetails/hp-prodesk-600-g4-small-form-factor-pc/21341193/swIte... ) it did apply. But, undervolting is still disabled because the release date of this BIOS is  November 2020, post-PlunderVolt, which was patched sometime in 2019 most likely. These Skylake-class CPUs can be undervolted stable often to 140mV with Throttlestop, and almostall to 110mV reducing power consumption of my farm but the 600 G4 is the model  I have trouble with. Prodesk 400 G5 for instance I don't believe I've ever not been able to rollback BIOS to get Undervolt enabled. I am not concerned with security. These machines do nothing at all but stock Windows 10 and BOINC 247365. Thanks for the research!

If I could disable Sure-start someway?