Re: [PATCH 1/1] tpm: add sysfs exports for all banks of PCR registers

[Mimi Zohar <zohar@linux.ibm.com>]

Hi James,

On Mon, 2020-07-20 at 08:00 -0700, James Bottomley wrote:
> use macro magic to create sysfs per hash groups with 24 PCR files in
> them one for each possible agile hash of the TPM.  The files are
> plugged in to a read function which is TPM version agnostic, so this
> works also for TPM 1.2 although the hash is only sha1 in that case.
> For every hash the TPM supports, a group named pcr-<hash> is created
> and each of the PCR read files placed under it.
> 
> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

Nice!  Being able to read the TPM 2.0 PCRs, without requiring a TSS,
will really simplify regression testing - re-calculating the IMA
"boot_aggregate" and verifying the IMA measurement list.

With the following code snippet all of the PCRs for all the exported
TPM banks are displayed, but unfortunately the digests are not ordered
or prefixed with the PCR.

banks=$(echo -n $(ls -d /sys/class/tpm/tpm0/pcr-*))

for bank in ${banks[@]}; do
        echo "$bank:"
        find "${bank}/" -type f -exec cat {} \;
        echo " "
done

Either this code snippet needs to be fixed or, perhaps, instead of
returning just the digest, the digest could be prefixed with the PCR
number (eg. PCR-00:<digest>).

FYI, with this patch on a system with TPM 1.2, IMA goes into TPM-
bypass mode.

From dmesg (with some extra debugging):
tpm_chip_register: tpm_add_legacy_sysfs failed
tpm_tis: probe of 00:05 failed with error -2

Mimi