[v5,0/2] add sysfs exports for TPM 2 PCR registers

Message

James Bottomley Jan. 13, 2021, 11:26 p.m. UTC

This represents v5 which has the spelling mistake fixed and the WARN
on unrecognized TPM hash algorithm becoming a dev_err.

We've had a fairly extensive discussion and iterated to agreement on
the output format, which becomes our ABI being one single compact hex
representation of the hash value per file according to sysfs rules,
with the file hierarchy going under

  /sys/class/tpm/tmp<x>/pcr-<hash>/<pcr number>

So to get the value of PCR 7 in the sha256 bank of the default TPM I'd do

   cat /sys/class/tpm/tpm0/pcr-sha256/7
   2ED93F199692DC6788EFA6A1FE74514AB9760B2A6CEEAEF6C808C13E4ABB0D42

If you need the binary hash of a set of PCRs, as is required for TPM
policy statements that lock to PCRs, you'd use something like:

  cat /sys/class/tpm/tpm0/pcr-sha256/{1,6,7}|xxd -r -p|sha256sum

Which produces the binary hash of PCRs 1, 6 and 7 in that order.

Note that this patch also adds the sha1 bank for TPM 1.2 in the same
manner (one file per PCR) but does not remove the existing pcrs file
which has the space separated all PCRs in one file format of

  PCR-00: 7D 29 CB 08 0C 0F C4 16 7A 0E 9A F7 C6 D3 97 CD C1 21 A7 69 
  PCR-01: 9C B6 79 4C E4 4B 62 97 4C AB 55 13 1A 2F 7E AE 09 B3 30 BE 
  ...

James

---

James Bottomley (2):
  tpm: add sysfs exports for all banks of PCR registers
  ABI: add sysfs description for tpm exports of PCR registers

 Documentation/ABI/stable/sysfs-class-tpm |  14 ++
 drivers/char/tpm/tpm-sysfs.c             | 179 +++++++++++++++++++++++
 include/linux/tpm.h                      |   9 +-
 3 files changed, 201 insertions(+), 1 deletion(-)