On Tue, Jun 10, 2025 at 07:03:32AM +0100, Yeoreum Yun wrote:

To integrate a TPM device that uses CRB over FF-A with the IMA subsystem,
both the tpm_crb and tpm_crb_ffa drivers must be built as built-in
(i.e., ARM_FFA_TRANSPORT=y, CONFIG_TCG_CRB=y, and CONFIG_TCG_CRB_FFA=y),
because IMA itself is built-in and the TPM device must be probed
before ima_init() is invoked during IMA subsystem initialization.

The description of the problem and motivation to solve it should be
first; not the actions taken.

To ensure this works correctly, the following initcalls must be executed in order:
	1.	ffa_init()
	2.	tpm_crb_ffa_driver_init()
	3.	crb_acpi_driver_init()

Unfortunately, the order of these device initcalls cannot be strictly controlled.
As a result:
	1.	ffa_init() may be called after tpm_crb_ffa_driver_init()
	2.	tpm_crb_ffa_driver_init() may be called after crb_acpi_driver_init()

For example, the following initcall sequence may occur:
  0000000000000888 l  .initcall6.init>  crb_acpi_driver_init
  000000000000088c l  .initcall6.init>  tpm_crb_ffa_driver_init

This symbol does not exist.

  0000000000000a9c l  .initcall6.init>  ffa_init

In this situation, the IMA subsystem fails to integrate with the TPM device
because the TPM was not available at the time ima_init() was called.
As a result, you may see the following message in the kernel log:

  | ima: No TPM chip found, activating TPM-bypass!

TPM initializes before IMA, so there should not be a problem.

BR, Jarkko