System time

Posted Jul 17, 2025 8:32 UTC (Thu) by aaribaud (subscriber, #87304)
In reply to: System time by tux3
Parent article: Linux and Secure Boot certificate expiration

> I have (not so) fond memories of old BIOS systems where removing the battery would reset
> both the settings and clock.
>
> I'm not sure if this is still a thing.</em>

It is not.

For decades now, the BIOS settings are not stored in volatile memory but in the BIOS Flash chip, where they survive as long as they are not reset through a BIOS menu command -- and if that BIOS has a master password set and you don't know it, then you can't enter the BIOS menu, and the only way out is either physically reprogramming the flash chip with a "blank" BIOS, or buying a new motherboard (ask me how I know. Better yet, don't ask).

Plus, about a decade ago, at least one BIOS provider, AMI, provided support for protecting the master password with the TPM, which--if applied by the BIOS vendor--basically removes the "physically reprogramming the flash chip" option.

System time

Posted Jul 18, 2025 0:35 UTC (Fri) by marcH (subscriber, #57642) [Link] (5 responses)

I recently lost all video outputs after trying some "unusual" BIOS settings (lesson learned...)

I realize it's different from a master password lockdown, but I found in the manual a way to reset settings with a jumper (no jumper actually needed, any small piece of metal worked). It worked!

System time

Posted Jul 18, 2025 21:03 UTC (Fri) by Lwnkhz (guest, #178382) [Link] (4 responses)

Not possible on TPM protected systems

System time

Posted Jul 18, 2025 21:18 UTC (Fri) by mjg59 (subscriber, #23239) [Link] (3 responses)

The TPM has nothing whatsoever to do with firmware settings or whether they can be reset.

System time

Posted Jul 18, 2025 22:06 UTC (Fri) by aaribaud (subscriber, #87304) [Link] (2 responses)

> The TPM has nothing whatsoever to do with firmware settings or whether they can be reset.

This rather depends on the context, notably whether and how the BIOS is TPM-protected.

System time

Posted Jul 18, 2025 22:54 UTC (Fri) by mjg59 (subscriber, #23239) [Link] (1 responses)

No, it doesn't. There's no such thing as a TPM-protected BIOS and even if there were that would have nothing to do with the firmware variables which are inherently mutable.

System time

Posted Jul 19, 2025 4:48 UTC (Sat) by aaribaud (subscriber, #87304) [Link]

> No, it doesn't. There's no such thing as a TPM-protected BIOS and even if there were that would have nothing to do with the firmware variables which are inherently mutable.

There appears to be such thing as a TPM-protected BIOS: https://trustedcomputinggroup.org/american-megatrends-sup...

And if there is such a BIOS, then when the master password is set, many settings become immutable.