From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jarkko Sakkinen Subject: Re: [PATCH v2 2/5] tpm: introduce tpm_pcr_algo_to_crypto() and tpm_pcr_algo_from_crypto() Date: Wed, 31 May 2017 14:40:41 +0300 Message-ID: <20170531114040.p3wwkc3soomweyd5@intel.com> References: <20170505142152.29795-1-roberto.sassu@huawei.com> <20170505142152.29795-3-roberto.sassu@huawei.com> <20170515111629.urjvbhqzohv4vakc@intel.com> <0deed9be-d0c3-3a69-d510-1c8aa3513ba8@huawei.com> <20170520132217.t7n7l2pjn7i63hbm@intel.com> <0b04a33c-248b-6597-473f-c5bc4ccaba62@huawei.com> <20170524173354.puyulkjmio3jgs2l@intel.com> <20170524202523.grpg7ocrwwuzxsbg@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: owner-linux-security-module@vger.kernel.org To: Roberto Sassu Cc: tpmdd-devel@lists.sourceforge.net, linux-ima-devel@lists.sourceforge.net, linux-security-module@vger.kernel.org, keyrings@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: tpmdd-devel@lists.sourceforge.net On Tue, May 30, 2017 at 12:24:21PM +0200, Roberto Sassu wrote: > 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 > > > > > > > > --- > > > > > > > > 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 > > -- > HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 > Managing Director: Bo PENG, Qiuen PENG, Shengli WANG Parameters should be changed when it makes sense to do so. It makes sense in this case. /Jarkko