-----Original Message----- From: Mimi Zohar [mailto:zohar@linux.ibm.com] Sent: Monday, March 2, 2020 2:42 PM To: Roberto Sassu roberto.sassu@huawei.com; James.Bottomley@HansenPartnership.com; jarkko.sakkinen@linux.intel.com; Dmitry Kasatkin dmitry.kasatkin@gmail.com Cc: linux-integrity@vger.kernel.org; linux-security-module@vger.kernel.org; linux-kernel@vger.kernel.org; Silviu Vlasceanu Silviu.Vlasceanu@huawei.com; stable@vger.kernel.org Subject: Re: [PATCH v3 2/8] ima: Switch to ima_hash_algo for boot aggregate
On Tue, 2020-02-11 at 10:09 +0000, Roberto Sassu wrote:
-----Original Message-----
Please find/use a mailer that doesn't include this junk.
I will do. I didn't have the time yet.
On Mon, 2020-02-10 at 11:00 +0100, Roberto Sassu wrote:
boot_aggregate is the first entry of IMA measurement list. Its purpose
is
to link pre-boot measurements to IMA measurements. As IMA was
designed to
work with a TPM 1.2, the SHA1 PCR bank was always selected.
Currently, even if a TPM 2.0 is used, the SHA1 PCR bank is selected. However, the assumption that the SHA1 PCR bank is always available is
not
correct, as PCR banks can be selected with the PCR_Allocate() TPM
command.
This patch tries to use ima_hash_algo as hash algorithm for
boot_aggregate.
If no PCR bank uses that algorithm, the patch tries to find the SHA256
PCR
bank (which is mandatory in the TCG PC Client specification).
Up to here, the patch description matches the code.
If also this bank is not found, the patch selects the first one. If the TPM algorithm of that bank is not mapped to a crypto ID, boot_aggregate is set to
zero.
This comment and the one inline are left over from previous version.
Hi Mimi
actually the code does what is described above. bank_idx is initially set to zero and remains as it is if there is no PCR bank for the default IMA algorithm or SHA256.
Sorry for the delay in continuing to review this patch set. It took a while to write ima-evm-utils regression tests for it.
Dmitry and you were the ones that initiated ima-evm-utils, saying there should a single package for signing files and integrity testing. The features in ima-evm-utils should reflect what is actually upstreamed in the kernel. (Currently there are a few experimental features which were never upstreamed. I'd like to remove them, but am a bit concerned that they are being used.) I'd appreciate your help in keeping ima-evm-utils up to date. It will help simplify upstreaming new kernel features.
My initial patch attempted to use any common TPM and kernel hash algorithm to calculate the boot_aggregate. The discussion with James was pretty clear, which you even stated in the Changelog. Either we use the IMA default hash algorithm, SHA256 for TPM 2.0 or SHA1 for TPM 1.2 for the boot-aggregate.
Ok, I didn't understand fully. I thought we should use the default IMA algorithm and select SHA256 as fallback choice for TPM 2.0 if there is no PCR bank for default algorithm. I additionally implemented the logic to select the first PCR bank if the SHA256 PCR bank is not available but I can remove it.
SHA256 should be the minimum requirement for boot aggregate. The advantage of using the default IMA algorithm is that it will be possible to select stronger algorithms when they are supported by the TPM. We might introduce a new option to specify only the algorithm for boot aggregate, like James suggested to support embedded systems. Let me know which option you prefer.
Thanks
Roberto
HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli