Re: [PATCH v5 2/4] security: ima: introduce IMA_INIT_LATE_SYNC option

[Yeoreum Yun <yeoreum.yun@arm.com>]

On Tue, Jun 02, 2026 at 08:35:52AM -0400, Mimi Zohar wrote:
> On Mon, 2026-06-01 at 15:27 +0100, Yeoreum Yun wrote:
> > To generate the boot_aggregate log in the IMA subsystem with TPM PCR values,
> > the TPM driver must be built as built-in and
> > must be probed before the IMA subsystem is initialized.
> > 
> > However, when the TPM device operates over the FF-A protocol using
> > the CRB interface, probing fails and returns -EPROBE_DEFER if
> > the tpm_crb_ffa device — an FF-A device that provides the communication
> > interface to the tpm_crb driver — has not yet been probed.
> > 
> > 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.
> > 
> > When this occurs, probing the TPM device is deferred.
> > However, the deferred probe can happen after the IMA subsystem
> > has already been initialized, since IMA initialization is performed
> > during late_initcall, and deferred_probe_initcall() is performed
> > at the same level.
> > 
> > And the similar situation is reported on TPM devices attached on SPI
> > bus[0].
> > 
> > To resolve this, introduce IMA_INIT_LATE_SYNC option to initialise
> > IMA at late_inicall_sync so that IMA is initialized with the TPM
> > device probed deferred.
> > 
> > When this option is enabled, modules that access files in the
> > initramfs through usermode helper calls such as request_module()
> > during initcall must not be built-in. Otherwise, IMA may miss
> > measuring those files [1].
> > 
> > Link: https://lore.kernel.org/all/aYXEepLhUouN5f99@earth.li/ [0]
> > Link: https://lore.kernel.org/all/2b3782398cc17ce9d355490a0c42ebce9120a9ae.camel@linux.ibm.com/ [1]
> > Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> 
> Reviewed-by:  Mimi Zohar <zohar@linux.ibm.com>

Thanks!

-- 
Sincerely,
Yeoreum Yun