Messages in this thread | | | Subject | Re: [PATCH v2 2/5] tpm: introduce tpm_pcr_algo_to_crypto() and tpm_pcr_algo_from_crypto() | From | Roberto Sassu <> | Date | Mon, 22 May 2017 09:21:28 +0200 |
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On 5/20/2017 3:22 PM, Jarkko Sakkinen wrote: > On Mon, May 15, 2017 at 04:22:22PM +0200, Roberto Sassu wrote: >> On 5/15/2017 1:16 PM, Jarkko Sakkinen wrote: >>> On Fri, May 05, 2017 at 04:21:49PM +0200, Roberto Sassu wrote: >>>> tpm_pcr_algorithms() returns to its callers the IDs of the hash algorithms >>>> supported by the TPM. This patch introduces tpm_pcr_algo_to_crypto(), >>>> so that the callers can use the crypto subsystem to calculate the digest >>>> to be passed to tpm_pcr_extend(). >>>> >>>> tpm_pcr_algo_from_crypto(), implemented for completeness, is instead used >>> >>> What do you mean by completeness? Please, never add unused stuff. >>> >>>> by tpm2_seal_trusted() to perform the opposite conversion. >>>> >>>> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> >>>> --- >>>> v2 >>>> >>>> - fixed return values of tpm2_pcr_algo_to_crypto() and >>>> tpm2_pcr_algo_from_crypto() if TPM support is disabled in the kernel >>> >>> Change Log only to the cover letter. >>> >>>> drivers/char/tpm/tpm-interface.c | 51 ++++++++++++++++++++++++++++++++++++++++ >>>> drivers/char/tpm/tpm2-cmd.c | 42 +++++++++------------------------ >>>> include/linux/tpm.h | 13 ++++++++++ >>>> 3 files changed, 75 insertions(+), 31 deletions(-) >>> >>> This commit is just deadly wrong in so many ways. >>> >>> I would suggest to make extend always just take crypto ID in so you >>> don't have to add these bizarre conversion functions. >> >> The reason of this choice (as I explained in the cover letter) >> is that TPM users might want to produce an event log with >> the TCG format (which includes the TPM algorithm ID). Also, >> TPM IDs should be preferred because, with them, TPM users >> can calculate a digest directly with the TPM. >> >> Taking crypto IDs means relying on the fact that there >> is always a mapping between TPM IDs and crypto IDs. >> Otherwise, tpm_pcr_algorithms() cannot return the algorithms >> to its callers and PCRs cannot be extended. If TPM IDs are used, >> TPM users have two alternatives: calculate the digest with >> the TPM, or pass a SHA1 digest to tpm_pcr_extend(), so that >> it can be padded to extend remanining PCR banks. >> >> However, this second option will work only when the TPM driver >> determines the size of an algorithm without relying on the crypto >> subsystem. At the moment, if a TPM ID is not mapped to a crypto ID, >> tpm2_pcr_extend() ignores the digest. >> >> Roberto > > What if tpm_pcr_algorithms would convert TPM IDs to crypto IDs? > > Externally other subsystems would have to then deal with only crypto > IDs.
Then, other subsystems cannot:
- use the TPM to calculate a digest - create an event log with the TCG format
Roberto
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