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The 60 seconds periodic update of the entropy pool >> that the hwrng kthread does triggers this, causing about 4 writes per >> requests. Makes 2 millions per year for a 24/7 device, and that is a lot >> for its backing NV storage. >> >> It is therefore better to make the user intentionally enable this, >> providing a chance to read the warning. >> >> [1] https://github.com/Microsoft/ms-tpm-20-ref >> >> Signed-off-by: Jan Kiszka > > Looking at DRBG_* from [1] I don't see anything you describe. If OPTEE > writes NVRAM, then the implementation is broken. It's not OP-TEE, but it might be indeed an artifact of the reference implementation that the fTPM is using because it is also targeting simulation: https://github.com/microsoft/ms-tpm-20-ref/blob/ee21db0a941decd3cac67925ea3310873af60ab3/TPMCmd/tpm/src/main/ExecCommand.c#L99 (Page 942 in [1]) -> ... -> https://github.com/microsoft/ms-tpm-20-ref/blob/main/TPMCmd/tpm/src/subsystem/Time.c#L68 (Page 1075 in [1]) > > Also AFAIK, it is pre-seeded per power cycle. There's nothing that even > distantly relates on using NVRAM. > > [1] https://trustedcomputinggroup.org/wp-content/uploads/TPM-2.0-1.83-Part-4-Supporting-Routines-Code.pdf > > BR, Jarkko Given how detailed [1] is, we likely need to address that directly there to avoid spreading this issue into fTPMs. Fact is, that there firmware implementations out there which exactly do what [1] suggests: writing to NV every 4 seconds on every command. Jan -- Siemens AG, Foundational Technologies Linux Expert Center