On Tue Aug 1, 2023 at 9:42 PM EEST, Linus Torvalds wrote: > On Tue, 1 Aug 2023 at 11:28, Jarkko Sakkinen <jarkko@xxxxxxxxxx> wrote: > > > > I would disable it inside tpm_crb driver, which is the driver used > > for fTPM's: they are identified by MSFT0101 ACPI identifier. > > > > I think the right scope is still AMD because we don't have such > > regressions with Intel fTPM. > > I'm ok with that. > > > I.e. I would move the helper I created inside tpm_crb driver, and > > a new flag, let's say "TPM_CHIP_FLAG_HWRNG_DISABLED", which tpm_crb > > sets before calling tpm_chip_register(). > > > > Finally, tpm_add_hwrng() needs the following invariant: > > > > if (chip->flags & TPM_CHIP_FLAG_HWRNG_DISABLED) > > return 0; > > > > How does this sound? I can refine this quickly from my first trial. > > Sounds fine. Mario, it would be good if you could send a fix candidate but take my suggestion for a new TPM chip flag into account, while doing it. Please send it as a separate patch, not attachment to this thread. I can test and ack it, if it looks reasonable. > My only worry comes from my ignorance: do these fTPM devices *always* > end up being enumerated through CRB, or do they potentially look > "normal enough" that you can actually end up using them even without > having that CRB driver loaded? I know that QEMU has TPM passthrough but I don't know how it behaves exactly. > Put another way: is the CRB driver the _only_ way they are visible, or > could some people hit on this through the TPM TIS interface if they > have CRB disabled? I'm not aware of such implementations. > I see, for example, that qemu ends up emulating the TIS layer, and it > might end up forwarding the TPM requests to something that is natively > CRB? > > But again: I don't know enough about CRB vs TIS, so the above may be a > stupid question. > > Linus I would focus exactly what is known not to work and disable exactly that. If someone still wants to enable TPM on such hardware, we can later on add a kernel command-line flag to enforce hwrng. This ofc based on user feedback, not something I would add right now. BR, Jarkko
