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
v3:
- remove end marker change
- replace active_banks static array with pointer to dynamic array
- remove TPM2_ACTIVE_PCR_BANKS
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 (6):
tpm: dynamically allocate active_banks array
tpm: remove definition of TPM2_ACTIVE_PCR_BANKS
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 the output of PCR read contains the correct digest
size
drivers/char/tpm/tpm-chip.c | 1 +
drivers/char/tpm/tpm-interface.c | 34 +++++---
drivers/char/tpm/tpm.h | 19 ++---
drivers/char/tpm/tpm2-cmd.c | 115 ++++++++++++++++++++--------
include/linux/tpm.h | 30 +++++++-
include/linux/tpm_eventlog.h | 12 +--
security/integrity/ima/ima_crypto.c | 10 +--
7 files changed, 145 insertions(+), 76 deletions(-)
--
2.17.1
