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: Sat, 20 May 2017 16:22:17 +0300 Message-ID: <20170520132217.t7n7l2pjn7i63hbm@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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <0deed9be-d0c3-3a69-d510-1c8aa3513ba8@huawei.com> 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 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. That would favor "memcpy" (or it would become a for loop) for 1/5. /Jarkko