On Tue, Oct 28, 2025 at 06:46:39AM +0100, Jan Kiszka wrote: > On 27.10.25 20:51, Jarkko Sakkinen wrote: > > On Tue, Oct 21, 2025 at 02:46:15PM +0200, Jan Kiszka wrote: > >> From: Jan Kiszka <[email protected]> > >> > >> As seen with optee_ftpm, which uses ms-tpm-20-ref [1], a TPM may write > >> the current time epoch to its NV storage every 4 seconds if there are > >> commands sent to it. 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 <[email protected]> > > > > 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.
We don't reference code as a certified hardware product, sorry. > > Jan > > -- > Siemens AG, Foundational Technologies > Linux Expert Center BR, Jarkko
