linux-kernel - Re: [PATCH v4 0/6] tpm: retrieve digest size of unknown algorithms from TPM

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Date:   Thu, 8 Nov 2018 15:51:40 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>
Cc:     zohar@...ux.ibm.com, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, silviu.vlasceanu@...wei.com
Subject: Re: [PATCH v4 0/6] tpm: retrieve digest size of unknown algorithms
 from TPM

On Tue, Nov 06, 2018 at 04:01:53PM +0100, Roberto Sassu wrote:
> 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
> 

You should rebase your series to the latest upstream.

/Jarkko