On Mon, 2018-11-19 at 09:16 +0100, Roberto Sassu wrote: > On 11/19/2018 5:57 AM, Mimi Zohar wrote: > > On Sun, 2018-11-18 at 09:27 +0200, Jarkko Sakkinen wrote: > >> On Fri, Nov 16, 2018 at 04:55:36PM +0100, Roberto Sassu wrote: > >>> On 11/16/2018 4:03 PM, Jarkko Sakkinen wrote: > >>>> On Wed, Nov 14, 2018 at 04:31:08PM +0100, Roberto Sassu wrote: > >>>>> Currently, tpm_pcr_extend() accepts as an input only a SHA1 digest. > >>>>> > >>>>> This patch modifies the definition of tpm_pcr_extend() to allow other > >>>>> kernel subsystems to pass a digest for each algorithm supported by the TPM. > >>>>> All digests are processed by the TPM in one operation. > >>>>> > >>>>> If a tpm_pcr_extend() caller provides a subset of the supported algorithms, > >>>>> the TPM driver extends the remaining PCR banks with the first digest > >>>>> passed as an argument to the function. > >>>> > >>>> What is the legit use case for this? > >>> > >>> A subset could be chosen for better performance, or when a TPM algorithm > >>> is not supported by the crypto subsystem. > >> > >> Doesn't extending a subset a security concern? > > > > Right, so instead of extending a subset of the allocated banks, all of > > the allocated banks need to be extended, even for those banks that a > > digest was not included. This is no different than what is being done > > today. IMA is currently only calculating the SHA1 hash, padding the > > digest with 0's, and extending the padded value(s) into all of the > > allocated banks. > > The caller of tpm_pcr_extend() could pass a subset of the allocated > banks, but the TPM driver extends all banks as before. Agreed, there should be a clear division. 1) The caller shouldn't need to know anything about the chip->info. 2) The TPM driver should not rely on the caller to supply all the hashes, but verify that all allocated banks are being extended. Mimi > > > > If there is a vulnerability with the hash algorithm, then any bank > > extended with the padded/truncated digest would be susceptible. > > > > IMA will need to become TPM 2.0 aware, calculating and extending > > multiple banks and define a new measurement list format containing the > > multiple digests. > > > > Mimi > > >
