linux-kernel - [PATCH v2 2/2] tpm: tpm_crb_ffa: manually register tpm_crb

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Message-Id: <20250610060334.2149041-3-yeoreum.yun@arm.com>
Date: Tue, 10 Jun 2025 07:03:34 +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 2/2] tpm: tpm_crb_ffa: manually register tpm_crb_ffa driver when it's built-in

To integrate tpm_event_log with IMA subsystem,
tpm_crb and tpm_crb_ffa driver should be built as built-in
(CONFIG_TCG_CRB=y && CONFIG_TCG_CRB_FFA=y) and
TPM device using CRB over FF-A should be probed
before ima_init() which is called as late_initcall.

However, we couldn't control the probing order between
crb_acpi_driver_init() and tpm_crb_ffa_driver_init() that's why
crb_acpi_driver_init() could be called before
tpm_crb_ffa_driver_init() when they're deployed like:

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

In this situation, the TPM device is queued deferred probing
and it can be handled later ima_init() caled in init_ima().

000000000000012c l       .initcall7.init>-0000000000000000 init_ima
000000000000016c l       .initcall7.init>-0000000000000000 deferred_probe_initcall7

When this happen, IMA fails to generate boot_aggregate with
TPM's PCR values so it prints below message:

   | ima: No TPM chip found, activating TPM-bypass!

To resolve this issue, the tpm_crb_ffa_init() function
attempts to probe the tpm_crb_ffa device.
This ensures that the TPM device using CRB over FF-A can be
successfully probed even if crb_acpi_driver_init() is called first.

Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
---
 drivers/char/tpm/tpm_crb_ffa.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/drivers/char/tpm/tpm_crb_ffa.c b/drivers/char/tpm/tpm_crb_ffa.c
index 4ead61f01299..2ef29b66fa5d 100644
--- a/drivers/char/tpm/tpm_crb_ffa.c
+++ b/drivers/char/tpm/tpm_crb_ffa.c
@@ -115,6 +115,7 @@ struct tpm_crb_ffa {
 };

 static struct tpm_crb_ffa *tpm_crb_ffa;
+static struct ffa_driver tpm_crb_ffa_driver;

 static int tpm_crb_ffa_to_linux_errno(int errno)
 {
@@ -168,13 +169,22 @@ static int tpm_crb_ffa_to_linux_errno(int errno)
  */
 int tpm_crb_ffa_init(void)
 {
-	if (!tpm_crb_ffa)
-		return -ENOENT;
+	int ret = 0;

-	if (IS_ERR_VALUE(tpm_crb_ffa))
-		return -ENODEV;
+	if (IS_MODULE(CONFIG_TCG_ARM_CRB_FFA)) {
+		if (!tpm_crb_ffa)
+			ret = -ENOENT;

-	return 0;
+		if (IS_ERR_VALUE(tpm_crb_ffa))
+			ret = -ENODEV;
+
+		return ret;
+	}
+
+	ret = ffa_register(&tpm_crb_ffa_driver);
+	BUG_ON(!ret && !tpm_crb_ffa);
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(tpm_crb_ffa_init);

@@ -369,7 +379,9 @@ static struct ffa_driver tpm_crb_ffa_driver = {
 	.id_table = tpm_crb_ffa_device_id,
 };

+#ifdef MODULE
 module_ffa_driver(tpm_crb_ffa_driver);
+#endif

 MODULE_AUTHOR("Arm");
 MODULE_DESCRIPTION("TPM CRB FFA driver");
--
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}