[v3,0/5] tpm: retrieve digest size of unknown algorithms from TPM

Message

Roberto Sassu Oct. 30, 2018, 3:47 p.m. UTC

The TPM driver currently relies on the crypto subsystem to determine the
digest size of supported TPM algorithms. In the future, TPM vendors might
implement new algorithms in their chips, and those algorithms might not
be supported by the crypto subsystem.

Usually, vendors provide patches for the new hardware, and likely
the crypto subsystem will be updated before the new algorithm is
introduced. However, old kernels might be updated later, after patches
are included in the mainline kernel. This would leave the opportunity
for attackers to misuse PCRs, as PCR banks with an unknown algorithm
are not extended.

This patch set provides a long term solution for this issue. If a TPM
algorithm is not known by the crypto subsystem, the TPM driver retrieves
the digest size from the TPM with a PCR read. All the PCR banks are
extended, even if the algorithm is not yet supported by the crypto
subsystem.

PCR bank information (TPM algorithm ID, digest size, crypto subsystem ID)
is stored in the tpm_chip structure and available for users of the TPM
driver.

Changelog

v2:
- change the end marker of the active_banks array
- check digest size from output of PCR read command
- remove count parameter from tpm_pcr_read() and tpm2_pcr_read()

v1:
- modify definition of tpm_pcr_read()
- move hash algorithms and definition of tpm2_digest to include/linux/tpm.h

Roberto Sassu (5):
  tpm: change the end marker of the active_banks array to zero
  tpm: rename and export tpm2_digest and tpm2_algorithms
  tpm: modify tpm_pcr_read() definition to pass a TPM hash algorithm
  tpm: retrieve digest size of unknown algorithms with PCR read
  tpm: ensure that output of PCR read contains the correct digest size

 drivers/char/tpm/tpm-interface.c    | 19 ++++--
 drivers/char/tpm/tpm.h              | 18 ++----
 drivers/char/tpm/tpm2-cmd.c         | 99 +++++++++++++++++++++--------
 include/linux/tpm.h                 | 30 ++++++++-
 include/linux/tpm_eventlog.h        |  9 +--
 security/integrity/ima/ima_crypto.c | 10 +--
 6 files changed, 122 insertions(+), 63 deletions(-)