[PATCH v8 1/5] tpm_crb: ffa_tpm: implement driver compliant to CRB over FF-A

Stuart Yoder
2025-03-12T21:58:37Z

The Arm specification TPM Service CRB over FF-A specification
defines the FF-A messages to interact with a CRB-based TPM
implemented as an FF-A secure partition.

Spec URL:
https://developer.arm.com/documentation/den0138/latest/

This driver is probed when a TPM Secure Partition is
discovered by the FF-A subsystem. It exposes APIs
used by the TPM CRB driver to send notifications to
the TPM.

Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Stuart Yoder <stuart.yoder@arm.com>
---
drivers/char/tpm/Kconfig | 9 +
drivers/char/tpm/Makefile | 1 +
drivers/char/tpm/tpm_crb_ffa.c | 348 +++++++++++++++++++++++++++++++++
drivers/char/tpm/tpm_crb_ffa.h | 25 +++
4 files changed, 383 insertions(+)
create mode 100644 drivers/char/tpm/tpm_crb_ffa.c
create mode 100644 drivers/char/tpm/tpm_crb_ffa.h

diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
index 0fc9a510e059..fe4f3a609934 100644
--- a/drivers/char/tpm/Kconfig
+++ b/drivers/char/tpm/Kconfig
@@ -210,6 +210,15 @@ config TCG_CRB
from within Linux. To compile this driver as a module, choose
M here; the module will be called tpm_crb.

+config TCG_ARM_CRB_FFA
+ tristate "TPM CRB over Arm FF-A Transport"
+ depends on ARM_FFA_TRANSPORT && TCG_CRB
+ default TCG_CRB
+ help
+ If the Arm FF-A transport is used to access the TPM say Yes.
+ To compile this driver as a module, choose M here; the module
+ will be called tpm_crb_ffa.
+
config TCG_VTPM_PROXY
tristate "VTPM Proxy Interface"
depends on TCG_TPM
diff --git a/drivers/char/tpm/Makefile b/drivers/char/tpm/Makefile
index 9bb142c75243..2b004df8c04b 100644
--- a/drivers/char/tpm/Makefile
+++ b/drivers/char/tpm/Makefile
@@ -42,5 +42,6 @@ obj-$(CONFIG_TCG_IBMVTPM) += tpm_ibmvtpm.o
obj-$(CONFIG_TCG_TIS_ST33ZP24) += st33zp24/
obj-$(CONFIG_TCG_XEN) += xen-tpmfront.o
obj-$(CONFIG_TCG_CRB) += tpm_crb.o
+obj-$(CONFIG_TCG_ARM_CRB_FFA) += tpm_crb_ffa.o
obj-$(CONFIG_TCG_VTPM_PROXY) += tpm_vtpm_proxy.o
obj-$(CONFIG_TCG_FTPM_TEE) += tpm_ftpm_tee.o
diff --git a/drivers/char/tpm/tpm_crb_ffa.c b/drivers/char/tpm/tpm_crb_ffa.c
new file mode 100644
index 000000000000..3169a87a56b6
--- /dev/null
+++ b/drivers/char/tpm/tpm_crb_ffa.c
@@ -0,0 +1,348 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2024 Arm Ltd.
+ *
+ * This device driver implements the TPM CRB start method
+ * as defined in the TPM Service Command Response Buffer
+ * Interface Over FF-A (DEN0138).
+ */
+
+#define pr_fmt(fmt) "CRB_FFA: " fmt
+
+#include <linux/arm_ffa.h>
+#include "tpm_crb_ffa.h"
+
+/* TPM service function status codes */
+#define CRB_FFA_OK 0x05000001
+#define CRB_FFA_OK_RESULTS_RETURNED 0x05000002
+#define CRB_FFA_NOFUNC 0x8e000001
+#define CRB_FFA_NOTSUP 0x8e000002
+#define CRB_FFA_INVARG 0x8e000005
+#define CRB_FFA_INV_CRB_CTRL_DATA 0x8e000006
+#define CRB_FFA_ALREADY 0x8e000009
+#define CRB_FFA_DENIED 0x8e00000a
+#define CRB_FFA_NOMEM 0x8e00000b
+
+#define CRB_FFA_VERSION_MAJOR 1
+#define CRB_FFA_VERSION_MINOR 0
+
+/* version encoding */
+#define CRB_FFA_MAJOR_VERSION_MASK GENMASK(30, 16)
+#define CRB_FFA_MINOR_VERSION_MASK GENMASK(15, 0)
+#define CRB_FFA_MAJOR_VERSION(x) ((u16)(FIELD_GET(CRB_FFA_MAJOR_VERSION_MASK, (x))))
+#define CRB_FFA_MINOR_VERSION(x) ((u16)(FIELD_GET(CRB_FFA_MINOR_VERSION_MASK, (x))))
+
+/*
+ * Normal world sends requests with FFA_MSG_SEND_DIRECT_REQ and
+ * responses are returned with FFA_MSG_SEND_DIRECT_RESP for normal
+ * messages.
+ *
+ * All requests with FFA_MSG_SEND_DIRECT_REQ and FFA_MSG_SEND_DIRECT_RESP
+ * are using the AArch32 SMC calling convention with register usage as
+ * defined in FF-A specification:
+ * w0: Function ID (0x8400006F or 0x84000070)
+ * w1: Source/Destination IDs
+ * w2: Reserved (MBZ)
+ * w3-w7: Implementation defined, free to be used below
+ */
+
+/*
+ * Returns the version of the interface that is available
+ * Call register usage:
+ * w3: Not used (MBZ)
+ * w4: TPM service function ID, CRB_FFA_GET_INTERFACE_VERSION
+ * w5-w7: Reserved (MBZ)
+ *
+ * Return register usage:
+ * w3: Not used (MBZ)
+ * w4: TPM service function status
+ * w5: TPM service interface version
+ * Bits[31:16]: major version
+ * Bits[15:0]: minor version
+ * w6-w7: Reserved (MBZ)
+ *
+ * Possible function status codes in register w4:
+ * CRB_FFA_OK_RESULTS_RETURNED: The version of the interface has been
+ * returned.
+ */
+#define CRB_FFA_GET_INTERFACE_VERSION 0x0f000001
+
+/*
+ * Return information on a given feature of the TPM service
+ * Call register usage:
+ * w3: Not used (MBZ)
+ * w4: TPM service function ID, CRB_FFA_START
+ * w5: Start function qualifier
+ * Bits[31:8] (MBZ)
+ * Bits[7:0]
+ * 0: Notifies TPM that a command is ready to be processed
+ * 1: Notifies TPM that a locality request is ready to be processed
+ * w6: TPM locality, one of 0..4
+ * -If the start function qualifier is 0, identifies the locality
+ * from where the command originated.
+ * -If the start function qualifier is 1, identifies the locality
+ * of the locality request
+ * w6-w7: Reserved (MBZ)
+ *
+ * Return register usage:
+ * w3: Not used (MBZ)
+ * w4: TPM service function status
+ * w5-w7: Reserved (MBZ)
+ *
+ * Possible function status codes in register w4:
+ * CRB_FFA_OK: the TPM service has been notified successfully
+ * CRB_FFA_INVARG: one or more arguments are not valid
+ * CRB_FFA_INV_CRB_CTRL_DATA: CRB control data or locality control
+ * data at the given TPM locality is not valid
+ * CRB_FFA_DENIED: the TPM has previously disabled locality requests and
+ * command processing at the given locality
+ */
+#define CRB_FFA_START 0x0f000201
+
+struct tpm_crb_ffa {
+ struct ffa_device *ffa_dev;
+ u16 major_version;
+ u16 minor_version;
+ /* lock to protect sending of FF-A messages: */
+ struct mutex msg_data_lock;
+ struct ffa_send_direct_data direct_msg_data;
+};
+
+static struct tpm_crb_ffa *tpm_crb_ffa;
+
+static int tpm_crb_ffa_to_linux_errno(int errno)
+{
+ int rc;
+
+ switch (errno) {
+ case CRB_FFA_OK:
+ rc = 0;
+ break;
+ case CRB_FFA_OK_RESULTS_RETURNED:
+ rc = 0;
+ break;
+ case CRB_FFA_NOFUNC:
+ rc = -ENOENT;
+ break;
+ case CRB_FFA_NOTSUP:
+ rc = -EPERM;
+ break;
+ case CRB_FFA_INVARG:
+ rc = -EINVAL;
+ break;
+ case CRB_FFA_INV_CRB_CTRL_DATA:
+ rc = -ENOEXEC;
+ break;
+ case CRB_FFA_ALREADY:
+ rc = -EEXIST;
+ break;
+ case CRB_FFA_DENIED:
+ rc = -EACCES;
+ break;
+ case CRB_FFA_NOMEM:
+ rc = -ENOMEM;
+ break;
+ default:
+ rc = -EINVAL;
+ }
+
+ return rc;
+}
+
+/**
+ * tpm_crb_ffa_init - called by the CRB driver to do any needed initialization
+ *
+ * This function is called by the tpm_crb driver during the tpm_crb
+ * driver's initialization. If the tpm_crb_ffa has not been probed
+ * yet, returns -ENOENT in order to force a retry. If th ffa_crb
+ * driver had been probed but failed with an error, returns -ENODEV
+ * in order to prevent further retries.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+int tpm_crb_ffa_init(void)
+{
+ if (!tpm_crb_ffa)
+ return -ENOENT;
+
+ if (IS_ERR_VALUE(tpm_crb_ffa))
+ return -ENODEV;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(tpm_crb_ffa_init);
+
+static int __tpm_crb_ffa_send_recieve(unsigned long func_id,
+ unsigned long a0,
+ unsigned long a1,
+ unsigned long a2)
+{
+ const struct ffa_msg_ops *msg_ops;
+ int ret;
+
+ if (!tpm_crb_ffa)
+ return -ENOENT;
+
+ msg_ops = tpm_crb_ffa->ffa_dev->ops->msg_ops;
+
+ memset(&tpm_crb_ffa->direct_msg_data, 0x00,
+ sizeof(struct ffa_send_direct_data));
+
+ tpm_crb_ffa->direct_msg_data.data1 = func_id;
+ tpm_crb_ffa->direct_msg_data.data2 = a0;
+ tpm_crb_ffa->direct_msg_data.data3 = a1;
+ tpm_crb_ffa->direct_msg_data.data4 = a2;
+
+ ret = msg_ops->sync_send_receive(tpm_crb_ffa->ffa_dev,
+ &tpm_crb_ffa->direct_msg_data);
+ if (!ret)
+ ret = tpm_crb_ffa_to_linux_errno(tpm_crb_ffa->direct_msg_data.data1);
+
+ return ret;
+}
+
+/**
+ * tpm_crb_ffa_get_interface_version() - gets the ABI version of the TPM service
+ * @major: Pointer to caller-allocated buffer to hold the major version
+ * number the ABI
+ * @minor: Pointer to caller-allocated buffer to hold the minor version
+ * number the ABI
+ *
+ * Returns the major and minor version of the ABI of the FF-A based TPM.
+ * Allows the caller to evaluate its compatibility with the version of
+ * the ABI.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+int tpm_crb_ffa_get_interface_version(u16 *major, u16 *minor)
+{
+ int rc;
+
+ if (!tpm_crb_ffa)
+ return -ENOENT;
+
+ if (IS_ERR_VALUE(tpm_crb_ffa))
+ return -ENODEV;
+
+ if (!major || !minor)
+ return -EINVAL;
+
+ guard(mutex)(&tpm_crb_ffa->msg_data_lock);
+
+ rc = __tpm_crb_ffa_send_recieve(CRB_FFA_GET_INTERFACE_VERSION, 0x00, 0x00, 0x00);
+ if (!rc) {
+ *major = CRB_FFA_MAJOR_VERSION(tpm_crb_ffa->direct_msg_data.data2);
+ *minor = CRB_FFA_MINOR_VERSION(tpm_crb_ffa->direct_msg_data.data2);
+ }
+
+ return rc;
+}
+EXPORT_SYMBOL_GPL(tpm_crb_ffa_get_interface_version);
+
+/**
+ * tpm_crb_ffa_start() - signals the TPM that a field has changed in the CRB
+ * @request_type: Identifies whether the change to the CRB is in the command
+ * fields or locality fields.
+ * @locality: Specifies the locality number.
+ *
+ * Used by the CRB driver
+ * that might be useful to those using or modifying it. Begins with
+ * empty comment line, and may include additional embedded empty
+ * comment lines.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+int tpm_crb_ffa_start(int request_type, int locality)
+{
+ if (!tpm_crb_ffa)
+ return -ENOENT;
+
+ if (IS_ERR_VALUE(tpm_crb_ffa))
+ return -ENODEV;
+
+ guard(mutex)(&tpm_crb_ffa->msg_data_lock);
+
+ return __tpm_crb_ffa_send_recieve(CRB_FFA_START, request_type, locality, 0x00);
+}
+EXPORT_SYMBOL_GPL(tpm_crb_ffa_start);
+
+static int tpm_crb_ffa_probe(struct ffa_device *ffa_dev)
+{
+ struct tpm_crb_ffa *p;
+ int rc;
+
+ /* only one instance of a TPM partition is supported */
+ if (tpm_crb_ffa && !IS_ERR_VALUE(tpm_crb_ffa))
+ return -EEXIST;
+
+ tpm_crb_ffa = ERR_PTR(-ENODEV); // set tpm_crb_ffa so we can detect probe failure
+
+ if (!ffa_partition_supports_direct_recv(ffa_dev)) {
+ pr_err("TPM partition doesn't support direct message receive.\n");
+ return -EINVAL;
+ }
+
+ p = kzalloc(sizeof(*tpm_crb_ffa), GFP_KERNEL);
+ if (!p)
+ return -ENOMEM;
+ tpm_crb_ffa = p;
+
+ mutex_init(&tpm_crb_ffa->msg_data_lock);
+ tpm_crb_ffa->ffa_dev = ffa_dev;
+ ffa_dev_set_drvdata(ffa_dev, tpm_crb_ffa);
+
+ /* if TPM is aarch32 use 32-bit SMCs */
+ if (!ffa_partition_check_property(ffa_dev, FFA_PARTITION_AARCH64_EXEC))
+ ffa_dev->ops->msg_ops->mode_32bit_set(ffa_dev);
+
+ /* verify compatibility of TPM service version number */
+ rc = tpm_crb_ffa_get_interface_version(&tpm_crb_ffa->major_version,
+ &tpm_crb_ffa->minor_version);
+ if (rc) {
+ pr_err("failed to get crb interface version. rc:%d", rc);
+ goto out;
+ }
+
+ pr_info("ABI version %u.%u", tpm_crb_ffa->major_version,
+ tpm_crb_ffa->minor_version);
+
+ if (tpm_crb_ffa->major_version != CRB_FFA_VERSION_MAJOR ||
+ (tpm_crb_ffa->minor_version > 0 &&
+ tpm_crb_ffa->minor_version < CRB_FFA_VERSION_MINOR)) {
+ pr_err("Incompatible ABI version");
+ goto out;
+ }
+
+ return 0;
+
+out:
+ kfree(tpm_crb_ffa);
+ tpm_crb_ffa = ERR_PTR(-ENODEV);
+ return -EINVAL;
+}
+
+static void tpm_crb_ffa_remove(struct ffa_device *ffa_dev)
+{
+ kfree(tpm_crb_ffa);
+ tpm_crb_ffa = NULL;
+}
+
+static const struct ffa_device_id tpm_crb_ffa_device_id[] = {
+ /* 17b862a4-1806-4faf-86b3-089a58353861 */
+ { UUID_INIT(0x17b862a4, 0x1806, 0x4faf,
+ 0x86, 0xb3, 0x08, 0x9a, 0x58, 0x35, 0x38, 0x61) },
+ {}
+};
+
+static struct ffa_driver tpm_crb_ffa_driver = {
+ .name = "ffa-crb",
+ .probe = tpm_crb_ffa_probe,
+ .remove = tpm_crb_ffa_remove,
+ .id_table = tpm_crb_ffa_device_id,
+};
+
+module_ffa_driver(tpm_crb_ffa_driver);
+
+MODULE_AUTHOR("Arm");
+MODULE_DESCRIPTION("TPM CRB FFA driver");
+MODULE_LICENSE("GPL");
diff --git a/drivers/char/tpm/tpm_crb_ffa.h b/drivers/char/tpm/tpm_crb_ffa.h
new file mode 100644
index 000000000000..645c41ede10e
--- /dev/null
+++ b/drivers/char/tpm/tpm_crb_ffa.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2024 Arm Ltd.
+ *
+ * This device driver implements the TPM CRB start method
+ * as defined in the TPM Service Command Response Buffer
+ * Interface Over FF-A (DEN0138).
+ */
+#ifndef _TPM_CRB_FFA_H
+#define _TPM_CRB_FFA_H
+
+#if IS_REACHABLE(CONFIG_TCG_ARM_CRB_FFA)
+int tpm_crb_ffa_init(void);
+int tpm_crb_ffa_get_interface_version(u16 *major, u16 *minor);
+int tpm_crb_ffa_start(int request_type, int locality);
+#else
+static inline int tpm_crb_ffa_init(void) { return 0; }
+static inline int tpm_crb_ffa_get_interface_version(u16 *major, u16 *minor) { return 0; }
+static inline int tpm_crb_ffa_start(int request_type, int locality) { return 0; }
+#endif
+
+#define CRB_FFA_START_TYPE_COMMAND 0
+#define CRB_FFA_START_TYPE_LOCALITY_REQUEST 1
+
+#endif
--
2.34.1