On 09.11.25 05:43, Jarkko Sakkinen wrote: > 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. >
Means what? Jan -- Siemens AG, Foundational Technologies Linux Expert Center
