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 | Tue, 30 May 2017 12:24:21 +0200 |
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On 5/24/2017 10:25 PM, Jarkko Sakkinen wrote: > On Wed, May 24, 2017 at 10:33:54AM -0700, Jarkko Sakkinen wrote: >> On Mon, May 22, 2017 at 09:21:28AM +0200, Roberto Sassu wrote: >>> 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 >> >> Can you open this up a bit? What is the use case that you canno >> implement? >> >> /Jarkko > > The most important question is: are this used *right now*. If not, it is > a definitive NAK. We don't want any future-proof code to the kernel. > Always do the lowest common denominator in terms of generality and we > will refactor from there when need arises.
This is still being discussed.
If we use crypto IDs, as you suggested, what it should be passed to tpm_pcr_extend()? Or, probably to a new function (Mimi said that changing the parameters of an existing function is not bisect-safe).
Roberto
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