[PATCH 1/4] tpm_crb: implement driver compliant to CRB over FF-A

Stuart Yoder
2025-02-10T23:22:39Z

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.

Signed-off-by: Stuart Yoder <stuart.yoder@arm.com>
---
drivers/char/tpm/Kconfig | 9 ++
drivers/char/tpm/Makefile | 1 +
drivers/char/tpm/ffa_crb.c | 310 +++++++++++++++++++++++++++++++++++++
drivers/char/tpm/ffa_crb.h | 30 ++++
4 files changed, 350 insertions(+)
create mode 100644 drivers/char/tpm/ffa_crb.c
create mode 100644 drivers/char/tpm/ffa_crb.h

diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
index 0fc9a510e059..f02af3925758 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_FFA_CRB
+ tristate "TPM CRB over Arm FF-A Transport"
+ depends on ARM_FFA_TRANSPORT
+ default y if (TCG_CRB && ARM_FFA_TRANSPORT)
+ 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 ffa_crb.
+
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..7c65368e18db 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-$(CONFIG_TCG_ARM_FFA_CRB) += ffa_crb.o
obj-$(CONFIG_TCG_VTPM_PROXY) += tpm_vtpm_proxy.o
obj-$(CONFIG_TCG_FTPM_TEE) += tpm_ftpm_tee.o
diff --git a/drivers/char/tpm/ffa_crb.c b/drivers/char/tpm/ffa_crb.c
new file mode 100644
index 000000000000..8f11e49956a8
--- /dev/null
+++ b/drivers/char/tpm/ffa_crb.c
@@ -0,0 +1,310 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2024 Arm Ltd.
+ *
+ * Maintained by: <tpmdd-devel@lists.sourceforge.net>
+ *
+ * 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) "FFA_CRB: " fmt
+
+#include <linux/arm_ffa.h>
+#include "ffa_crb.h"
+
+/* TPM service function status codes */
+#define FFA_CRB_OK 0x05000001
+#define FFA_CRB_OK_RESULTS_RETURNED 0x05000002
+#define FFA_CRB_NOFUNC 0x8e000001
+#define FFA_CRB_NOTSUP 0x8e000002
+#define FFA_CRB_INVARG 0x8e000005
+#define FFA_CRB_INV_CRB_CTRL_DATA 0x8e000006
+#define FFA_CRB_ALREADY 0x8e000009
+#define FFA_CRB_DENIED 0x8e00000a
+#define FFA_CRB_NOMEM 0x8e00000b
+
+#define FFA_CRB_VERSION_MAJOR 1
+#define FFA_CRB_VERSION_MINOR 0
+
+/* version encoding */
+#define FFA_CRB_MAJOR_VERSION_MASK GENMASK(30, 16)
+#define FFA_CRB_MINOR_VERSION_MASK GENMASK(15, 0)
+#define FFA_CRB_MAJOR_VERSION(x) ((u16)(FIELD_GET(FFA_CRB_MAJOR_VERSION_MASK, (x))))
+#define FFA_CRB_MINOR_VERSION(x) ((u16)(FIELD_GET(FFA_CRB_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, FFA_CRB_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 FFA_CRB_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, FFA_CRB_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:
+ * FFA_CRB_OK: the TPM service has been notified successfully
+ * FFA_CRB_INVARG: one or more arguments are not valid
+ * FFA_CRB_INV_CRB_CTRL_DATA: CRB control data or locality control
+ * data at the given TPM locality is not valid
+ * FFA_CRB_DENIED: the TPM has previously disabled locality requests and
+ * command processing at the given locality
+ */
+#define FFA_CRB_START 0x0f000201
+
+struct ffa_crb {
+ struct ffa_device *ffa_dev;
+ u16 major_version;
+ u16 minor_version;
+ struct mutex msg_data_lock;
+ struct ffa_send_direct_data direct_msg_data;
+};
+
+static struct ffa_crb *ffa_crb;
+
+static int ffa_crb_to_linux_errno(int errno)
+{
+ int rc;
+
+ switch (errno) {
+ case FFA_CRB_OK:
+ rc = 0;
+ break;
+ case FFA_CRB_OK_RESULTS_RETURNED:
+ rc = 0;
+ break;
+ case FFA_CRB_NOFUNC:
+ rc = -ENOENT;
+ break;
+ case FFA_CRB_NOTSUP:
+ rc = -EPERM;
+ break;
+ case FFA_CRB_INVARG:
+ rc = -EINVAL;
+ break;
+ case FFA_CRB_INV_CRB_CTRL_DATA:
+ rc = -ENOEXEC;
+ break;
+ case FFA_CRB_ALREADY:
+ rc = -EEXIST;
+ break;
+ case FFA_CRB_DENIED:
+ rc = -EACCES;
+ break;
+ case FFA_CRB_NOMEM:
+ rc = -ENOMEM;
+ break;
+ default:
+ rc = -EINVAL;
+ }
+
+ return rc;
+}
+
+int ffa_crb_init(void)
+{
+ if (ffa_crb == NULL)
+ return -ENOENT;
+
+ if (IS_ERR_VALUE(ffa_crb))
+ return -ENODEV;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(ffa_crb_init);
+
+static int __ffa_crb_send_recieve(unsigned long func_id,
+ unsigned long a0, unsigned long a1, unsigned long a2)
+{
+ int ret;
+ const struct ffa_msg_ops *msg_ops;
+
+ if (ffa_crb == NULL)
+ return -ENOENT;
+
+ msg_ops = ffa_crb->ffa_dev->ops->msg_ops;
+
+ memset(&ffa_crb->direct_msg_data, 0x00,
+ sizeof(struct ffa_send_direct_data));
+
+ ffa_crb->direct_msg_data.data1 = func_id;
+ ffa_crb->direct_msg_data.data2 = a0;
+ ffa_crb->direct_msg_data.data3 = a1;
+ ffa_crb->direct_msg_data.data4 = a2;
+
+ ret = msg_ops->sync_send_receive(ffa_crb->ffa_dev,
+ &ffa_crb->direct_msg_data);
+ if (!ret)
+ ret = ffa_crb_to_linux_errno(ffa_crb->direct_msg_data.data1);
+
+ return ret;
+}
+
+int ffa_crb_get_interface_version(uint16_t *major, uint16_t *minor)
+{
+ int rc;
+
+ if (ffa_crb == NULL)
+ return -ENOENT;
+
+ if (IS_ERR_VALUE(ffa_crb))
+ return -ENODEV;
+
+ if (major == NULL || minor == NULL)
+ return -EINVAL;
+
+ guard(mutex)(&ffa_crb->msg_data_lock);
+
+ rc = __ffa_crb_send_recieve(FFA_CRB_GET_INTERFACE_VERSION, 0x00, 0x00, 0x00);
+ if (!rc) {
+ *major = FFA_CRB_MAJOR_VERSION(ffa_crb->direct_msg_data.data2);
+ *minor = FFA_CRB_MINOR_VERSION(ffa_crb->direct_msg_data.data2);
+ }
+
+ return rc;
+}
+EXPORT_SYMBOL_GPL(ffa_crb_get_interface_version);
+
+int ffa_crb_start(int request_type, int locality)
+{
+ if (ffa_crb == NULL)
+ return -ENOENT;
+
+ if (IS_ERR_VALUE(ffa_crb))
+ return -ENODEV;
+
+ guard(mutex)(&ffa_crb->msg_data_lock);
+
+ return __ffa_crb_send_recieve(FFA_CRB_START, request_type, locality, 0x00);
+}
+EXPORT_SYMBOL_GPL(ffa_crb_start);
+
+static int ffa_crb_probe(struct ffa_device *ffa_dev)
+{
+ int rc;
+ struct ffa_crb *p;
+
+ /* only one instance of a TPM partition is supported */
+ if (ffa_crb && !IS_ERR_VALUE(ffa_crb))
+ return -EEXIST;
+
+ ffa_crb = ERR_PTR(-ENODEV); // set ffa_crb 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(*ffa_crb), GFP_KERNEL);
+ if (!p)
+ return -ENOMEM;
+ ffa_crb = p;
+
+ mutex_init(&ffa_crb->msg_data_lock);
+ ffa_crb->ffa_dev = ffa_dev;
+ ffa_dev_set_drvdata(ffa_dev, ffa_crb);
+
+ /* 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 = ffa_crb_get_interface_version(&ffa_crb->major_version,
+ &ffa_crb->minor_version);
+ if (rc) {
+ pr_err("failed to get crb interface version. rc:%d", rc);
+ goto out;
+ }
+
+ pr_info("ABI version %u.%u", ffa_crb->major_version,
+ ffa_crb->minor_version);
+
+ if ((ffa_crb->major_version != FFA_CRB_VERSION_MAJOR) ||
+ (ffa_crb->minor_version < FFA_CRB_VERSION_MINOR)) {
+ pr_err("Incompatible ABI version");
+ goto out;
+ }
+
+ return 0;
+
+out:
+ kfree(ffa_crb);
+ ffa_crb = ERR_PTR(-ENODEV);
+ return -EINVAL;
+}
+
+static void ffa_crb_remove(struct ffa_device *ffa_dev)
+{
+ kfree(ffa_crb);
+ ffa_crb = NULL;
+}
+
+static const struct ffa_device_id ffa_crb_device_id[] = {
+ /* 17b862a4-1806-4faf-86b3-089a58353861 */
+ { UUID_INIT(0x17b862a4, 0x1806, 0x4faf,
+ 0x86, 0xb3, 0x08, 0x9a, 0x58, 0x35, 0x38, 0x61) },
+ {}
+};
+
+static struct ffa_driver ffa_crb_driver = {
+ .name = "ffa-crb",
+ .probe = ffa_crb_probe,
+ .remove = ffa_crb_remove,
+ .id_table = ffa_crb_device_id,
+};
+
+module_ffa_driver(ffa_crb_driver);
+
+MODULE_AUTHOR("Arm");
+MODULE_DESCRIPTION("FFA CRB driver");
+MODULE_VERSION("1.0");
+MODULE_LICENSE("GPL");
diff --git a/drivers/char/tpm/ffa_crb.h b/drivers/char/tpm/ffa_crb.h
new file mode 100644
index 000000000000..42327d285165
--- /dev/null
+++ b/drivers/char/tpm/ffa_crb.h
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2024 Arm Ltd.
+ *
+ * Authors:
+ * Stuart Yoder <stuart.yoder@arm.com>
+ *
+ * Maintained by: <tpmdd-devel@lists.sourceforge.net>
+ *
+ * This device driver implements the TPM CRB start method
+ * as defined in the TPM Service Command Response Buffer
+ * Interface Over FF-A (DEN0138).
+ */
+#ifndef _FFA_CRB_H
+#define _FFA_CRB_H
+
+#if IS_ENABLED(CONFIG_TCG_ARM_FFA_CRB)
+int ffa_crb_init(void);
+int ffa_crb_get_interface_version(uint16_t *major, uint16_t *minor);
+int ffa_crb_start(int request_type, int locality);
+#else
+static inline int ffa_crb_init(void) { return 0; }
+static inline int ffa_crb_get_interface_version(uint16_t *major, uint16_t *minor) { return 0; }
+static inline int ffa_crb_start(int request_type, int locality) { return 0; }
+#endif
+
+#define FFA_CRB_START_TYPE_COMMAND 0
+#define FFA_CRB_START_TYPE_LOCALITY_REQUEST 1
+
+#endif
--
2.34.1