TPM PCR0 recontruction fails on Pluton fTPM

[Masum Reza]

My Gigabyte UEFI BIOS has an option to select which TPM chip to use. By default it uses AMD fTPM. After manually enabling Pluton fTPM via Gigabyte UEFI, TPM PCR0 reconstruction status changed to Invalid.

Ubuntu Version: 23.10
Kernel: Xanmod 6.6.8, Generic 6.5.0-14
Version: org.freedesktop.fwupd 1.9.5

Log

```
Host Security ID: HSI:1 (v1.9.5)

HSI-1
✔ Fused platform: Locked
✔ Supported CPU: Valid
✔ TPM empty PCRs: Valid
✔ TPM v2.0: Found
✔ UEFI bootservice variables: Locked
✔ UEFI platform key: Valid
✔ UEFI secure boot: Enabled

HSI-2
✔ IOMMU: Enabled
✔ Platform debugging: Locked
✔ SPI write protection: Enabled
✘ TPM PCR0 reconstruction: Invalid

HSI-3
✔ Pre-boot DMA protection: Enabled
✘ SPI replay protection: Not supported
✘ Suspend-to-idle: Disabled
✘ Suspend-to-ram: Enabled

HSI-4
✘ Encrypted RAM: Not supported
✘ Processor rollback protection: Disabled

Runtime Suffix -!
✔ Linux kernel: Untainted
✔ Linux kernel lockdown: Enabled
✔ Linux swap: Encrypted
✔ fwupd plugins: Untainted

The TPM PCR0 differs from reconstruction.
 » https://fwupd.github.io/hsi.html#pcr0-tpm-event-log-reconstruction

Host Security Events
  2023-12-25 18:39:14: ✘ TPM PCR0 reconstruction changed: Valid → Invalid
```

[Seth Arnold (seth-arnold)]

Thanks for the report, Masum.

I'm not sure if this is actually a bug against fwupd or just that fwupd is the tool that reported the change.

And it's entirely possible that this is the correct outcome. If the TPM device changes on a system, it's suddenly a very different system.

Hopefully someone more familiar with what's being done here will have some input; I suspect this is all "working as intended".

Thanks

[Mario Limonciello (superm1)]

The way this works is that the tpm event log is used to attempt to reconstruct pcr0. If it doesn't match the value in the tpm pcr0 then there is a bug or malware.

The same report was brought into fwupd upstream.
Various artifacts were captured and the conclusion is this is a BIOS bug.

It should be reported to the board vendor to be fixed.

https://github.com/fwupd/fwupd/issues/6574

[Seth Arnold (seth-arnold)]

Thanks Mario and Masum for working this through.