linux-kernel - Re: [PATCH v4 0/2] generate boot_aggregate log in IMA with TPM using CRB over FF-A

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Message-ID: <aFvRI5OwSLLKz300@e129823.arm.com>
Date: Wed, 25 Jun 2025 11:36:19 +0100
From: Yeoreum Yun <yeoreum.yun@....com>
To: Jarkko Sakkinen <jarkko@...nel.org>
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 v4 0/2] generate boot_aggregate log in IMA with TPM using
 CRB over FF-A

Hi Jarkko,

> On Wed, Jun 18, 2025 at 11:23:00AM +0100, Yeoreum Yun wrote:
> > To ensure the TPM device operating over the FF-A protocol with
> > the CRB interface is probed before IMA initialization,
> > the following conditions must be met:
> >
> >    1. The corresponding ffa_device must be registered,
> >       which is done via ffa_init().
> >
> >    2. The tpm_crb_driver must successfully probe this device via
> >       tpm_crb_ffa_init().
> >
> >    3. The tpm_crb driver using CRB over FF-A can then
> >       be probed successfully. (See crb_acpi_add() and
> >       tpm_crb_ffa_init() for reference.)
> >
> > Unfortunately, ffa_init(), tpm_crb_ffa_init(), and crb_acpi_driver_init() are
> > all registered with device_initcall, which means crb_acpi_driver_init() may
> > be invoked before ffa_init() and tpm_crb_ffa_init() are completed.
>
> I get the ffa_init() part i.e, moving it earlier. However for
> tpm_crb_ffa_init() and crb_acpi_driver_init(), modules.dep
> takes care that they are loaded in order.
> For IMA you will need the driver as built-in but that should
> be handled via kernel config, not via code changes.

In the case of "module" built, it's true.
However what I tell here is when "tpm_crb" and "tpm_crb_ffa" is built
as "built-in" in this case, it couldn't make a "dependency" between
the same initcall level: here is the case of this.

0000000000000888 l       .initcall6.init>-------0000000000000000 crb_acpi_driver_init
000000000000088c l       .initcall6.init>-------0000000000000000 tpm_crb_ffa_driver_init

in this case, wihtout code change, the crb_acpi_driver_init()
is failed since tpm_crb_ffa_driver_init() is called later.

and this couldn't be solved with kconfig --
ARM_FFA_TRANSPORT=y && CONFIG_TCG_CRB=y && CONFIG_TCG_CRB_FFA=y.

The Patch #2 is to proing the tpm_crb_ffa as part of
crb_acpi_driver_init() when TPM uses method ARM-FFA.

If there's another suggestion, let me know please.

Thanks

--
Sincerely,
Yeoreum Yun