Hi Joel, On Tue, 2020-09-29 at 06:14 +0000, Joel Stanley wrote: > On Fri, 25 Sep 2020 at 18:19, Mimi Zohar <zo...@linux.ibm.com> wrote: > > > > Hi Nayna, > > > > On Wed, 2020-09-23 at 14:25 -0400, Nayna Jain wrote: > > > Currently, skiroot_defconfig CONFIG_I2C_OPAL is built as a loadable > > > module rather than builtin, even if CONFIG_I2C=y is defined. This > > > results in a delay in the TPM initialization, causing IMA to go into > > > TPM bypass mode. As a result, the IMA measurements are added to the > > > measurement list, but do not extend the TPM. Because of this, it is > > > impossible to verify or attest to the system's integrity, either from > > > skiroot or the target Host OS. > > > > The patch description is good, but perhaps we could provide a bit more > > context before. > > > > The concept of trusted boot requires the measurement to be added to the > > measurement list and extend the TPM, prior to allowing access to the > > file. By allowing access to a file before its measurement is included > > in the measurement list and extended into the TPM PCR, a malicious file > > could potentially prevent its own measurement from being added. As the > > PCRs are tamper proof, measuring and extending the TPM prior to giving > > access to the file, guarantees that all file measurements are included > > in the measurement list, including the malicious file. > > > > IMA needs to be enabled before any files are accessed in order to > > verify a file's integrity and extend the TPM with the file > > measurement. Queueing file measurements breaks the measure and extend, > > before usage, trusted boot paradigm. > > > > The ima-evm-utils package includes a test for walking the IMA > > measurement list, calculating the expected TPM PCRs, and comparing the > > calculated PCR values with the physical TPM. Testing is important to > > ensure the TPM is initialized prior to IMA. Failure to validate the > > IMA measurement list may indicate IMA went into TPM bypass mode, like > > in this case. > > Thanks for the explanation Mimi. It's lucky that the TPM drivers can > be loaded early enough! > > Should we add something like this to security/integrity/ima/Kconfig? > > select I2C_OPAL if PPC_POWERNV > > It's generally frowned upon to select user visible symbols, but IMA > does this for the TCG options already.
The other examples enable the TPM. I2C_OPAL is dependent on I2C being builtin. I'm not sure if this select is complete, nor if this is where it belongs. Mimi
