tpm2_key_protector: Dump PCRs on policy fail

tpm2_key_protector: Dump PCRs on policy fail

PCR mismatch is one common cause of TPM key unsealing fail. Since the
system may be compromised, it is not safe to boot into OS to get the PCR
values and TPM eventlog for the further investigation.

To provide some hints, GRUB now dumps PCRs on policy fail, so the user
can check the current PCR values. PCR 0~15 are chosen to cover the
firmware, bootloader, and OS.

The sample output:

PCR Mismatch! Check firmware and bootloader before typing passphrase!
TPM PCR [sha256]:
  00: 17401f37710984c1d8a03a81fff3ab567ae9291bac61e21715b890ee28879738
  01: 7a114329ba388445a96e8db2a072785937c1b7a8803ed7cc682b87f3ff3dd7a8
  02: 11c2776849e8e24b7d80c926cbc4257871bffa744dadfefd3ed049ce25143e05
  03: 6c33b362073e28e30b47302bbdd3e6f9cee4debca3a304e646f8c68245724350
  04: 62d38838483ecfd2484ee3a2e5450d8ca3b35fc72cda6a8c620f9f43521c37d1
  05: d8a85cb37221ab7d1f2cc5f554dbe0463acb6784b5b8dc3164ccaa66d8fff0e1
  06: 9262e37cbe71ed4daf815b4a4881fb7251c9d371092dde827557d5368121e10e
  07: 219d542233be492d62b079ffe46cf13396a8c27e520e88b08eaf2e6d3b7e70f5
  08: de1f61c973b673e505adebe0d7e8fb65fde6c24dd4ab4fbaff9e28b18df6ecd3
  09: c1de7274fa3e879a16d7e6e7629e3463d95f68adcfd17c477183846dccc41c89
  10: 0000000000000000000000000000000000000000000000000000000000000000
  11: 0000000000000000000000000000000000000000000000000000000000000000
  12: 0000000000000000000000000000000000000000000000000000000000000000
  13: 0000000000000000000000000000000000000000000000000000000000000000
  14: 9ab9ebe4879a7f4dd00c04f37e79cfd69d0dd7a8bcc6b01135525b67676a3e40
  15: 0000000000000000000000000000000000000000000000000000000000000000
  16: 0000000000000000000000000000000000000000000000000000000000000000
  17: ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
  18: ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
  19: ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
  20: ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
  21: ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
  22: ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
  23: 0000000000000000000000000000000000000000000000000000000000000000
error: failed to unseal sealed key (TPM2_Unseal: 0x99d).
error: no key protector provided a usable key for luks (af16e48f-746b-4a12-aae1-c14dcee429e0).

If the user happens to have the PCR values for key sealing, the PCR dump
can be used to identify the changed PCRs and narrow down the scope for
closer inspection.

Please note that the PCR dump is trustworthy only if the GRUB binary is
authentic, so the user has to check the GRUB binary thoroughly before
using the PCR dump.

Signed-off-by: Gary Lin <glin@suse.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>