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TPM GPIO fail: How bad OEM firmware ruins Intel TPM security
In this article I demonstrate a software only attack that allows an operating system to set the PCRs of a discrete TPM device to arbitrary values and unseal any secret that uses a PCR based sealing policy (such as disk encryption keys used by unattended unlock TPM FDE schemes).
This then allows the same software that did the GPIO write operation to derive any desired PCR values similar to the hardware attack, but this time without any physical access to pins on the mainbaord. For one time disk decryption, the tweezer attack is just as effective, and is arguably faster to execute then overwriting the platform's flash. This claim is justified by the statement the NDA-only BIOS writer's guide supposedly includes guidance for OEMs on how and when to set the GPIO lock bits.
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