Re: [PATCH v3 0/4] TPM 2.0 fixes in IMA tests

[Petr Vorel <pvorel@suse.cz>]

Hi Jarkko,

can rely on /dev/tpm0 and /dev/tpmrm0 for TPM detection?
i.e.:
/dev/tpmrm0 => TPM 2.0
/dev/tpm0 => both TPM 1.2 or 2.0
none of them => No TPM device

I'm trying to get reliably TPM version (1, 2 or no TPM) for various kernel
versions (including very old ones like 3.x):

So far I have:

cat /sys/class/tpm/tpm0/tpm_version_major

[ -f /sys/class/tpm/tpm0/device/caps -o -f /sys/class/misc/tpm0/device/caps ] => TPM 1.2

[ ! -d /sys/class/tpm/tpm0/ -a ! -d /sys/class/misc/tpm0/ ] => no TPM

Then I grep
dmesg | grep -q 'activating TPM-bypass' => no TPM
dmesg | grep -q '1\.2 TPM (device-id' => TPM 1.2
dmesg | grep -q '2\.0 TPM (device-id' => TPM 2.0

But according to Mimi there are still some TPM 2.0 devices which does not export
sysfs files.

And I'd prefer avoid using dmesg (not on some embedded targets and not sure if
reliable for all TPM devices).

If I understand James's commit fdc915f7f719 ("tpm: expose spaces via a device link /dev/tpmrm<n>")
from v4.12-rc1 correctly /dev/tpmrm0 is really for TPM 2.0. But how to detect it
for v4.0 - v4.11 when /sys/class/tpm detection fails?
I haven't found anything obvious in drivers/char/tpm/tpm2-cmd.c from v4.0.

Thanks for info.

Kind regards,
Petr