linux-kernel - Re: [PATCH v4 1/2] firmware: arm_ffa: Change initcall level of ffa_init() to rootfs

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Message-ID: <47dbda783e5919a8137e3781472fe7ae94ee1c73.camel@linux.ibm.com>
Date: Sun, 22 Jun 2025 08:22:41 -0400
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Yeoreum Yun <yeoreum.yun@....com>, 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
Subject: Re: [PATCH v4 1/2] firmware: arm_ffa: Change initcall level of
 ffa_init() to rootfs_initcall

On Wed, 2025-06-18 at 11:23 +0100, Yeoreum Yun wrote:
> The Linux IMA (Integrity Measurement Architecture) subsystem used for secure
> boot, file integrity, or remote attestation cannot be a loadable module
> for few reasons listed below:
> 
>  o Boot-Time Integrity: IMA’s main role is to measure and appraise files
>    before they are used. This includes measuring critical system files during
>    early boot (e.g., init, init scripts, login binaries). If IMA were a module,
>    it would be loaded too late to cover those.
> 
>  o TPM Dependency: IMA integrates tightly with the TPM to record measurements
>    into PCRs. The TPM must be initialized early (ideally before init_ima()),
>    which aligns with IMA being built-in.
> 
>  o Security Model: IMA is part of a Trusted Computing Base (TCB). Making it a
>    module would weaken the security model, as a potentially compromised system
>    could delay or tamper with its initialization.
> 
> IMA must be built-in to ensure it starts measuring from the earliest possible
> point in boot which inturn implies TPM must be initialised and ready to use
> before IMA.
> 
> To enable integration of tpm_event_log with the IMA subsystem, the TPM drivers
> (tpm_crb and tpm_crb_ffa) also needs to be built-in. However with FF-A driver
> also being initialised at device initcall level, it can lead to an
> initialization order issue where:
>  - crb_acpi_driver_init() may run before tpm_crb_ffa_driver()_init and ffa_init()
>  - As a result, probing the TPM device via CRB over FFA is deferred
>  - ima_init() (called as a late initcall) runs before deferred probe completes,
>    IMA fails to find the TPM and logs the below error:
> 
>    |  ima: No TPM chip found, activating TPM-bypass!
> 
> Eventually it fails to generate boot_aggregate with PCR values.
> 
> Because of the above stated dependency, the ffa driver needs to initialised
> before tpm_crb_ffa module to ensure IMA finds the TPM successfully when
> present.
> 
> Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>

Thank you for the well written patch description.

> ---
>  drivers/firmware/arm_ffa/driver.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/arm_ffa/driver.c b/drivers/firmware/arm_ffa/driver.c
> index fe55613a8ea9..1a690b8186df 100644
> --- a/drivers/firmware/arm_ffa/driver.c
> +++ b/drivers/firmware/arm_ffa/driver.c
> @@ -2058,7 +2058,7 @@ static int __init ffa_init(void)
>  	kfree(drv_info);
>  	return ret;
>  }
> -module_init(ffa_init);
> +rootfs_initcall(ffa_init);

LGTM as the driver is always builtin.

Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>

>  
>  static void __exit ffa_exit(void)
>  {