Message-ID: <Z670QLo_FefvuNb8@kernel.org>
Date: Fri, 14 Feb 2025 09:44:00 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Stuart Yoder <stuart.yoder@....com>
Cc: linux-integrity@...r.kernel.org, peterhuewe@....de, jgg@...pe.ca,
	sudeep.holla@....com, rafael@...nel.org, lenb@...nel.org,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/5] tpm_crb: implement driver compliant to CRB over
 FF-A

On Thu, Feb 13, 2025 at 06:27:41PM -0600, 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.
> 
> Signed-off-by: Stuart Yoder <stuart.yoder@....com>
> ---
>  drivers/char/tpm/Kconfig       |   9 +
>  drivers/char/tpm/Makefile      |   1 +
>  drivers/char/tpm/tpm_crb_ffa.c | 310 +++++++++++++++++++++++++++++++++
>  drivers/char/tpm/tpm_crb_ffa.h |  30 ++++
>  4 files changed, 350 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..4c85b8c00b12 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
> +	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 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..3bd9fd81ec21
> --- /dev/null
> +++ b/drivers/char/tpm/tpm_crb_ffa.c
> @@ -0,0 +1,310 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2024 Arm Ltd.
> + *
> + * Maintained by: <tpmdd-devel@...ts.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) "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;
> +	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;
> +}
> +
> +int tpm_crb_ffa_init(void)
> +{
> +	if (tpm_crb_ffa == NULL)
> +		return -ENOENT;
> +
> +	if (IS_ERR_VALUE(tpm_crb_ffa))
> +		return -ENODEV;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(tpm_crb_ffa_init);

Should be documented given export [1].

> +
> +static int __tpm_crb_ffa_send_recieve(unsigned long func_id,
> +		unsigned long a0, unsigned long a1, unsigned long a2)
> +{
> +	int ret;
> +	const struct ffa_msg_ops *msg_ops;

Reverse tree-order would be easier for brain.

> +
> +	if (tpm_crb_ffa == NULL)

You probably did not run checkpatch.pl with '--strict', did you? ;-)

> +		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;
> +}
> +
> +int tpm_crb_ffa_get_interface_version(uint16_t *major, uint16_t *minor)
> +{
> +	int rc;
> +
> +	if (tpm_crb_ffa == NULL)
> +		return -ENOENT;
> +
> +	if (IS_ERR_VALUE(tpm_crb_ffa))
> +		return -ENODEV;
> +
> +	if (major == NULL || minor == NULL)
> +		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);

Ditto.

> +
> +int tpm_crb_ffa_start(int request_type, int locality)
> +{
> +	if (tpm_crb_ffa == NULL)
> +		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);

Ditto.

> +
> +static int tpm_crb_ffa_probe(struct ffa_device *ffa_dev)
> +{
> +	int rc;
> +	struct tpm_crb_ffa *p;
> +
> +	/* 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 < 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("FFA CRB driver");
> +MODULE_VERSION("1.0");
> +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..da73c299c48c
> --- /dev/null
> +++ b/drivers/char/tpm/tpm_crb_ffa.h
> @@ -0,0 +1,30 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2024 Arm Ltd.
> + *
> + * Authors:
> + * Stuart Yoder <stuart.yoder@....com>
> + *
> + * Maintained by: <tpmdd-devel@...ts.sourceforge.net>

Please, rip off this authors and maintainers clutter:

1. Git maintains authorship
2. MAINTAINERS takes care of the rest.

> 
> + *
> + * 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_ENABLED(CONFIG_TCG_ARM_CRB_FFA)
> +int tpm_crb_ffa_init(void);
> +int tpm_crb_ffa_get_interface_version(uint16_t *major, uint16_t *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(uint16_t *major, uint16_t *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
> 
> 

[1] https://www.kernel.org/doc/Documentation/kernel-doc-nano-HOWTO.txt

BR, Jarkko

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