Messages in this thread | | | Subject | Re: [PATCH v6 7/7] tpm: pass an array of tpm_bank_list structures to tpm_pcr_extend() | From | Roberto Sassu <> | Date | Thu, 13 Dec 2018 08:57:17 +0100 |
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On 12/12/2018 7:27 PM, Jarkko Sakkinen wrote: > On Thu, Dec 06, 2018 at 07:38:30PM +0100, Roberto Sassu wrote: >> On 12/5/2018 1:14 AM, Jarkko Sakkinen wrote: >>> On Tue, Dec 04, 2018 at 09:21:38AM +0100, Roberto Sassu wrote: >>>> The new tpm_bank_list structure has been preferred to the tpm_digest >>>> structure, to let the caller specify the size of the digest (which may be >>>> unknown to the TPM driver). >>> >>> Why is that? Didn't previous commit query these? >> >> Since the TPM driver pads/truncates the first digest passed by the >> caller to extend PCRs for which no digest was provided, it must know >> which amount of data it can use. It is possible that the algorithm of >> the first digest is unknown for the TPM driver, if the caller of >> tpm_pcr_extend() didn't check chip->allocated_banks. >> >> By requiring that the caller passes also the digest size, this problem >> does not arise. It seems reasonable to me to pass this information, as >> the caller calculated the digest and it should know the digest size. > > OK. I noticed something other things that look to alarming: > > 1. The function does not fail if alg_id is not found. This will go > silent.
It is intentional. If alg_id is not found, the PCR is extended with the first digest passed by the caller of tpm_pcr_extend(). If no digest was provided, the PCR is extended with 0s. This is done to prevent that PCRs in unused banks are extended later with fake measurements.
> 2. The function does not fail if there is a mismatch with the digest > sizes.
The data passed by the caller of tpm_pcr_extend() is copied to dummy_hash, which has the maximum length. Then, tpm2_pcr_extend() takes from dummy_hash as many bytes as needed, depending on the current algorithm.
Roberto
> /Jarkko >
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