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

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Message-ID: <aEgmhwu1RP27yBpw@kernel.org>
Date: Tue, 10 Jun 2025 15:35:19 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: sudeep.holla@....com, peterhuewe@....de, jgg@...pe.ca,
	stuart.yoder@....com, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org
Subject: Re: [PATCH v2 0/2] fix failure of integration IMA with tpm_crb_ffa

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