linux-kernel - [PATCH v2 0/2] fix failure of integration IMA with tpm_crb

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Message-Id: <20250610060334.2149041-1-yeoreum.yun@arm.com>
Date: Tue, 10 Jun 2025 07:03:32 +0100
From: Yeoreum Yun <yeoreum.yun@....com>
To: jarkko@...nel.org,
	sudeep.holla@....com,
	peterhuewe@....de,
	jgg@...pe.ca,
	stuart.yoder@....com
Cc: linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-integrity@...r.kernel.org,
	Yeoreum Yun <yeoreum.yun@....com>
Subject: [PATCH v2 0/2] fix failure of integration IMA with tpm_crb_ffa

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.

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
  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!

To resolve this issue:
  Patch #1: change the initcall level of ffa_init() to rootfs_initcall,
            so that the FF-A device is created before any FF-A drivers are loaded.

  Patch #2: call ffa_register() in tpm_crb_ffa_init() when it is built as built-in,
            ensuring that the Secure Partition used by tpm_crb_ffa
            is already registered when the TPM device is probed.

==============
Patch History
==============
  Since v1:
     - rewrite commit message.
     - https://lore.kernel.org/all/20250606105754.1202649-1-yeoreum.yun@arm.com/


Yeoreum Yun (2):
  firmware: arm_ffa: Change initcall level of ffa_init() to
    rootfs_initcall
  tpm: tpm_crb_ffa: maunally register tpm_crb_ffa driver when it's
    built-in

 drivers/char/tpm/tpm_crb_ffa.c    | 22 +++++++++++++++++-----
 drivers/firmware/arm_ffa/driver.c |  2 +-
 2 files changed, 18 insertions(+), 6 deletions(-)

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