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

Jarkko Sakkinen
2025-03-14T15:02:14Z

On Wed, Mar 12, 2025 at 04:58:24PM -0500, Stuart Yoder wrote:
> 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>

nit: should have been removed given the build issue (to make
apparent the need for review).

> 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)

Yes, this is correct given that it returns false on "vmlinux -> module"
situation ("vmlinux -> vmlinux" and "module -> module" still work).

> +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
>
>

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

[applying next week]

BR, Jarkko