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Date:   Wed, 15 May 2019 11:12:50 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     Sasha Levin <sashal@kernel.org>
Cc:     peterhuewe@gmx.de, jgg@ziepe.ca, corbet@lwn.net,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-integrity@vger.kernel.org, linux-kernel@microsoft.com,
        thiruan@microsoft.com, bryankel@microsoft.com
Subject: Re: [PATCH v3 1/2] ftpm: firmware TPM running in TEE
Message-ID: <20190515081250.GA7708@linux.intel.com>
References: <20190415155636.32748-1-sashal@kernel.org>
 <20190415155636.32748-2-sashal@kernel.org>
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On Mon, Apr 15, 2019 at 11:56:35AM -0400, Sasha Levin wrote:
> This patch adds support for a software-only implementation of a TPM
> running in TEE.
> 
> There is extensive documentation of the design here:
> https://www.microsoft.com/en-us/research/publication/ftpm-software-implementation-tpm-chip/ .
> 
> As well as reference code for the firmware available here:
> https://github.com/Microsoft/ms-tpm-20-ref/tree/master/Samples/ARM32-FirmwareTPM

The commit message should include at least a brief description what TEE
is.

> 
> Signed-off-by: Thirupathaiah Annapureddy <thiruan@microsoft.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  drivers/char/tpm/Kconfig        |   5 +
>  drivers/char/tpm/Makefile       |   1 +
>  drivers/char/tpm/tpm_ftpm_tee.c | 366 ++++++++++++++++++++++++++++++++
>  drivers/char/tpm/tpm_ftpm_tee.h |  47 ++++
>  4 files changed, 419 insertions(+)
>  create mode 100644 drivers/char/tpm/tpm_ftpm_tee.c
>  create mode 100644 drivers/char/tpm/tpm_ftpm_tee.h
> 
> diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
> index 536e55d3919f..5638726641eb 100644
> --- a/drivers/char/tpm/Kconfig
> +++ b/drivers/char/tpm/Kconfig
> @@ -164,6 +164,11 @@ config TCG_VTPM_PROXY
>  	  /dev/vtpmX and a server-side file descriptor on which the vTPM
>  	  can receive commands.
>  
> +config TCG_FTPM_TEE
> +	tristate "TEE based fTPM Interface"
> +	depends on TEE
> +	---help---
> +	  This driver proxies for fTPM running in TEE
>  
>  source "drivers/char/tpm/st33zp24/Kconfig"
>  endif # TCG_TPM
> diff --git a/drivers/char/tpm/Makefile b/drivers/char/tpm/Makefile
> index a01c4cab902a..c354cdff9c62 100644
> --- a/drivers/char/tpm/Makefile
> +++ b/drivers/char/tpm/Makefile
> @@ -33,3 +33,4 @@ obj-$(CONFIG_TCG_TIS_ST33ZP24) += st33zp24/
>  obj-$(CONFIG_TCG_XEN) += xen-tpmfront.o
>  obj-$(CONFIG_TCG_CRB) += tpm_crb.o
>  obj-$(CONFIG_TCG_VTPM_PROXY) += tpm_vtpm_proxy.o
> +obj-$(CONFIG_TCG_FTPM_TEE) += tpm_ftpm_tee.o
> diff --git a/drivers/char/tpm/tpm_ftpm_tee.c b/drivers/char/tpm/tpm_ftpm_tee.c
> new file mode 100644
> index 000000000000..f33cdfeb5376
> --- /dev/null
> +++ b/drivers/char/tpm/tpm_ftpm_tee.c
> @@ -0,0 +1,366 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) Microsoft Corporation
> + */

There should be at least some description what kind of implementation
this is and something about TEE.

> +
> +#include <linux/of.h>
> +#include <linux/of_platform.h>
> +#include <linux/acpi.h>
> +#include <linux/platform_device.h>
> +#include <linux/tee_drv.h>
> +#include <linux/uuid.h>
> +#include <linux/tpm.h>
> +
> +#include "tpm.h"
> +#include "tpm_ftpm_tee.h"
> +
> +#define DRIVER_NAME "ftpm-tee"
> +
> +/* TA_FTPM_UUID: BC50D971-D4C9-42C4-82CB-343FB7F37896 */
> +static const uuid_t ftpm_ta_uuid =
> +	UUID_INIT(0xBC50D971, 0xD4C9, 0x42C4,
> +		  0x82, 0xCB, 0x34, 0x3F, 0xB7, 0xF3, 0x78, 0x96);

Just wondering why prefixes are here in different order in the comment
and code.

> +
> +/*
> + * Note: ftpm_tee_tpm_op_recv and ftpm_tee_tpm_op_send are called from the
> + * same routine tpm_try_transmit in tpm-interface.c. These calls are protected
> + * by chip->tpm_mutex => There is no need for protecting any data shared
> + * between these routines ex: struct ftpm_tee_private
> + */

This documentation block should be removed. It could be in all drivers
and thus this documentation belongs outside of specific HW drivers.

> +
> +/**
> + * ftpm_tee_tpm_op_recv retrieve fTPM response.
> + * @param: chip, the tpm_chip description as specified in driver/char/tpm/tpm.h.
> + * @param: buf,	the buffer to store data.
> + * @param: count, the number of bytes to read.
> + * @return: In case of success the number of bytes received.
> + *	    In other case, a < 0 value describing the issue.
> + */

This should be modified to follow kdoc [1]. It is inconsistent with the
other kdoc comments we have. Now it is all wrong and contains redundant
information. It should be something like

/**
 * ftpm_tee_tpm_op_recv() - retrieve a response from fTPM
 * @chip:	TPM chip associated with the fTPM
 * @buf:	buffer for the received data
 * @count:	number of bytes to read
 *
 * Copy the response from fTPM's internal buffer to the buffer provided
 * by the caller.
 *
 * Return:
 *   0 on success,
 *   -errno on error
 */

> +static int ftpm_tee_tpm_op_recv(struct tpm_chip *chip, u8 *buf, size_t count)
> +{
> +	struct ftpm_tee_private *pvt_data = dev_get_drvdata(chip->dev.parent);
> +	size_t len;
> +
> +	len = pvt_data->resp_len;
> +	if (count < len) {
> +		dev_err(&chip->dev,
> +			"%s:Invalid size in recv: count=%zd, resp_len=%zd\n",
> +			__func__, count, len);
> +		return -EIO;
> +	}
> +
> +	memcpy(buf, pvt_data->resp_buf, len);
> +	pvt_data->resp_len = 0;
> +
> +	return len;
> +}
> +
> +/**
> + * ftpm_tee_tpm_op_send send TPM commands through the TEE shared memory.
> + *
> + * @param: chip, the tpm_chip description as specified in driver/char/tpm/tpm.h
> + * @param: buf,	the buffer to send.
> + * @param: len, the number of bytes to send.
> + * @return: In case of success, returns 0.
> + *	    In other case, a < 0 value describing the issue.
> + */

This should be modified to follow kdoc [1]. It is inconsistent with the
other kdoc comments we have.


> +static int ftpm_tee_tpm_op_send(struct tpm_chip *chip, u8 *buf, size_t len)
> +{
> +	struct ftpm_tee_private *pvt_data = dev_get_drvdata(chip->dev.parent);
> +	size_t resp_len;
> +	int rc;
> +	u8 *temp_buf;
> +	struct tpm_header *resp_header;
> +	struct tee_ioctl_invoke_arg transceive_args;
> +	struct tee_param command_params[4];
> +	struct tee_shm *shm = pvt_data->shm;
> +
> +	if (len > MAX_COMMAND_SIZE) {
> +		dev_err(&chip->dev,
> +			"%s:len=%zd exceeds MAX_COMMAND_SIZE supported by fTPM TA\n",
> +			__func__, len);
> +		return -EIO;
> +	}
> +
> +	memset(&transceive_args, 0, sizeof(transceive_args));
> +	memset(command_params, 0, sizeof(command_params));
> +	pvt_data->resp_len = 0;
> +
> +	/* Invoke FTPM_OPTEE_TA_SUBMIT_COMMAND function of fTPM TA */
> +	transceive_args = (struct tee_ioctl_invoke_arg) {
> +		.func = FTPM_OPTEE_TA_SUBMIT_COMMAND,
> +		.session = pvt_data->session,
> +		.num_params = 4,
> +	};
> +
> +	/* Fill FTPM_OPTEE_TA_SUBMIT_COMMAND parameters */
> +	command_params[0] = (struct tee_param) {
> +		.attr = TEE_IOCTL_PARAM_ATTR_TYPE_MEMREF_INPUT,
> +		.u.memref = {
> +			.shm = shm,
> +			.size = len,
> +			.shm_offs = 0,
> +		},
> +	};
> +
> +	temp_buf = tee_shm_get_va(shm, 0);
> +	if (IS_ERR(temp_buf)) {
> +		dev_err(&chip->dev, "%s:tee_shm_get_va failed for transmit\n",
> +			__func__);
> +		return PTR_ERR(temp_buf);
> +	}
> +	memset(temp_buf, 0, (MAX_COMMAND_SIZE + MAX_RESPONSE_SIZE));
> +
> +	memcpy(temp_buf, buf, len);
> +
> +	command_params[1] = (struct tee_param) {
> +		.attr = TEE_IOCTL_PARAM_ATTR_TYPE_MEMREF_INOUT,
> +		.u.memref = {
> +			.shm = shm,
> +			.size = MAX_RESPONSE_SIZE,
> +			.shm_offs = MAX_COMMAND_SIZE,
> +		},
> +	};
> +
> +	rc = tee_client_invoke_func(pvt_data->ctx, &transceive_args,
> +					command_params);
> +	if ((rc < 0) || (transceive_args.ret != 0)) {
> +		dev_err(&chip->dev, "%s:SUBMIT_COMMAND invoke error: 0x%x\n",
> +			__func__, transceive_args.ret);
> +		return (rc < 0) ? rc : transceive_args.ret;
> +	}
> +
> +	temp_buf = tee_shm_get_va(shm, command_params[1].u.memref.shm_offs);
> +	if (IS_ERR(temp_buf)) {
> +		dev_err(&chip->dev, "%s:tee_shm_get_va failed for receive\n",
> +			__func__);
> +		return PTR_ERR(temp_buf);
> +	}
> +
> +	resp_header = (struct tpm_header *)temp_buf;
> +	resp_len = be32_to_cpu(resp_header->length);
> +
> +	/* sanity check resp_len */
> +	if (resp_len < TPM_HEADER_SIZE) {
> +		dev_err(&chip->dev, "%s:tpm response header too small\n",
> +			__func__);
> +		return -EIO;
> +	}
> +	if (resp_len > MAX_RESPONSE_SIZE) {
> +		dev_err(&chip->dev,
> +			"%s:resp_len=%zd exceeds MAX_RESPONSE_SIZE\n",
> +			__func__, resp_len);
> +		return -EIO;
> +	}
> +
> +	/* sanity checks look good, cache the response */
> +	memcpy(pvt_data->resp_buf, temp_buf, resp_len);
> +	pvt_data->resp_len = resp_len;
> +
> +	return 0;
> +}
> +
> +static void ftpm_tee_tpm_op_cancel(struct tpm_chip *chip)
> +{
> +	/* not supported */
> +}
> +
> +static u8 ftpm_tee_tpm_op_status(struct tpm_chip *chip)
> +{
> +	return 0;
> +}
> +
> +static bool ftpm_tee_tpm_req_canceled(struct tpm_chip *chip, u8 status)
> +{
> +	return 0;
> +}
> +
> +static const struct tpm_class_ops ftpm_tee_tpm_ops = {
> +	.flags = TPM_OPS_AUTO_STARTUP,
> +	.recv = ftpm_tee_tpm_op_recv,
> +	.send = ftpm_tee_tpm_op_send,
> +	.cancel = ftpm_tee_tpm_op_cancel,
> +	.status = ftpm_tee_tpm_op_status,
> +	.req_complete_mask = 0,
> +	.req_complete_val = 0,
> +	.req_canceled = ftpm_tee_tpm_req_canceled,
> +};
> +
> +/*
> + * Check whether this driver supports the fTPM TA in the TEE instance
> + * represented by the params (ver/data) to this function.
> + */
> +static int ftpm_tee_match(struct tee_ioctl_version_data *ver, const void *data)
> +{
> +	/*
> +	 * Currently this driver only support GP Complaint OPTEE based fTPM TA
> +	 */
> +	if ((ver->impl_id == TEE_IMPL_ID_OPTEE) &&
> +		(ver->gen_caps & TEE_GEN_CAP_GP))
> +		return 1;
> +	else
> +		return 0;
> +}
> +
> +/*
> + * Undo what has been done in ftpm_tee_probe
> + */
> +static void ftpm_tee_deinit(struct ftpm_tee_private *pvt_data)
> +{
> +	/* Release the chip */
> +	tpm_chip_unregister(pvt_data->chip);
> +
> +	/* frees chip */
> +	if (pvt_data->chip)
> +		put_device(&pvt_data->chip->dev);
> +
> +	if (pvt_data->ctx) {
> +		/* Free the shared memory pool */
> +		tee_shm_free(pvt_data->shm);
> +
> +		/* close the existing session with fTPM TA*/
> +		tee_client_close_session(pvt_data->ctx, pvt_data->session);
> +
> +		/* close the context with TEE driver */
> +		tee_client_close_context(pvt_data->ctx);
> +	}
> +
> +	/* memory allocated with devm_kzalloc() is freed automatically */
> +}
> +
> +/**
> + * ftpm_tee_probe initialize the fTPM
> + * @param: pdev, the platform_device description.
> + * @return: 0 in case of success.
> + *	 or a negative value describing the error.
> + */
> +static int ftpm_tee_probe(struct platform_device *pdev)
> +{
> +	int rc;
> +	struct tpm_chip *chip;
> +	struct device *dev = &pdev->dev;
> +	struct ftpm_tee_private *pvt_data = NULL;
> +	struct tee_ioctl_open_session_arg sess_arg;
> +
> +	pvt_data = devm_kzalloc(dev, sizeof(struct ftpm_tee_private),
> +				GFP_KERNEL);
> +	if (!pvt_data)
> +		return -ENOMEM;
> +
> +	dev_set_drvdata(dev, pvt_data);
> +
> +	/* Open context with TEE driver */
> +	pvt_data->ctx = tee_client_open_context(NULL, ftpm_tee_match, NULL,
> +						NULL);
> +	if (IS_ERR(pvt_data->ctx)) {
> +		dev_err(dev, "%s:tee_client_open_context failed\n", __func__);
> +		return -EPROBE_DEFER;
> +	}
> +
> +	/* Open a session with fTPM TA */
> +	memset(&sess_arg, 0, sizeof(sess_arg));
> +	memcpy(sess_arg.uuid, ftpm_ta_uuid.b, TEE_IOCTL_UUID_LEN);
> +	sess_arg.clnt_login = TEE_IOCTL_LOGIN_PUBLIC;
> +	sess_arg.num_params = 0;
> +
> +	rc = tee_client_open_session(pvt_data->ctx, &sess_arg, NULL);
> +	if ((rc < 0) || (sess_arg.ret != 0)) {
> +		dev_err(dev, "%s:tee_client_open_session failed, err=%x\n",
> +			__func__, sess_arg.ret);
> +		rc = -EINVAL;
> +		goto out_tee_session;
> +	}
> +	pvt_data->session = sess_arg.session;
> +
> +	/* Allocate dynamic shared memory with fTPM TA */
> +	pvt_data->shm = tee_shm_alloc(pvt_data->ctx,
> +				(MAX_COMMAND_SIZE + MAX_RESPONSE_SIZE),
> +				TEE_SHM_MAPPED | TEE_SHM_DMA_BUF);
> +	if (IS_ERR(pvt_data->shm)) {
> +		dev_err(dev, "%s:tee_shm_alloc failed\n", __func__);
> +		rc = -ENOMEM;
> +		goto out_shm_alloc;
> +	}
> +
> +	/* Allocate new struct tpm_chip instance */
> +	chip = tpm_chip_alloc(dev, &ftpm_tee_tpm_ops);
> +	if (IS_ERR(chip)) {
> +		dev_err(dev, "%s:tpm_chip_alloc failed\n", __func__);
> +		rc = PTR_ERR(chip);
> +		goto out_chip_alloc;
> +	}
> +
> +	pvt_data->chip = chip;
> +	pvt_data->chip->flags |= TPM_CHIP_FLAG_TPM2;
> +
> +	/* Create a character device for the fTPM */
> +	rc = tpm_chip_register(pvt_data->chip);
> +	if (rc) {
> +		dev_err(dev, "%s:tpm_chip_register failed with rc=%d\n",
> +			__func__, rc);
> +		goto out_chip;
> +	}
> +
> +	return 0;
> +
> +out_chip:
> +	put_device(&pvt_data->chip->dev);
> +out_chip_alloc:
> +	tee_shm_free(pvt_data->shm);
> +out_shm_alloc:
> +	tee_client_close_session(pvt_data->ctx, pvt_data->session);
> +out_tee_session:
> +	tee_client_close_context(pvt_data->ctx);
> +
> +	return rc;
> +}
> +
> +/**
> + * ftpm_tee_remove remove the TPM device
> + * @param: pdev, the platform_device description.
> + * @return: 0 in case of success.
> + */
> +static int ftpm_tee_remove(struct platform_device *pdev)
> +{
> +	struct ftpm_tee_private *pvt_data = dev_get_drvdata(&pdev->dev);
> +
> +	/* Release the chip */
> +	tpm_chip_unregister(pvt_data->chip);
> +
> +	/* frees chip */
> +	put_device(&pvt_data->chip->dev);
> +
> +	/* Free the shared memory pool */
> +	tee_shm_free(pvt_data->shm);
> +
> +	/* close the existing session with fTPM TA*/
> +	tee_client_close_session(pvt_data->ctx, pvt_data->session);
> +
> +	/* close the context with TEE driver */
> +	tee_client_close_context(pvt_data->ctx);
> +
> +        /* memory allocated with devm_kzalloc() is freed automatically */
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id of_ftpm_tee_ids[] = {
> +	{ .compatible = "microsoft,ftpm" },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, of_ftpm_tee_ids);
> +
> +static struct platform_driver ftpm_tee_driver = {
> +	.driver = {
> +		.name = DRIVER_NAME,
> +		.of_match_table = of_match_ptr(of_ftpm_tee_ids),
> +	},
> +	.probe = ftpm_tee_probe,
> +	.remove = ftpm_tee_remove,
> +};
> +
> +module_platform_driver(ftpm_tee_driver);
> +
> +MODULE_AUTHOR("Thirupathaiah Annapureddy <thiruan@microsoft.com>");
> +MODULE_DESCRIPTION("TPM Driver for fTPM TA in TEE");
> +MODULE_LICENSE("GPL v2");
> diff --git a/drivers/char/tpm/tpm_ftpm_tee.h b/drivers/char/tpm/tpm_ftpm_tee.h
> new file mode 100644
> index 000000000000..9de513e72dbb
> --- /dev/null
> +++ b/drivers/char/tpm/tpm_ftpm_tee.h
> @@ -0,0 +1,47 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) Microsoft Corporation
> + */
> +
> +#ifndef __TPM_FTPM_TEE_H__
> +#define __TPM_FTPM_TEE_H__
> +
> +#include <linux/tee_drv.h>
> +#include <linux/uuid.h>
> +#include <linux/tpm.h>
> +
> +/* The TAFs ID implemented in this TA */
> +#define FTPM_OPTEE_TA_SUBMIT_COMMAND  (0)
> +#define FTPM_OPTEE_TA_EMULATE_PPI     (1)
> +
> +/* max. buffer size supported by fTPM  */
> +#define  MAX_COMMAND_SIZE       4096
> +#define  MAX_RESPONSE_SIZE      4096
> +
> +/**
> + * struct ftpm_tee_private - fTPM's private data
> + * @chip:     struct tpm_chip instance registered with tpm framework.
> + * @state:    internal state
> + * @session:  fTPM TA session identifier.
> + * @resp_len: cached response buffer length.
> + * @resp_buf: cached response buffer.
> + * @ctx:      TEE context handler.
> + * @shm:      Memory pool shared with fTPM TA in TEE.
> + */
> +struct ftpm_tee_private {
> +	struct tpm_chip *chip;
> +	u32 session;
> +	size_t resp_len;
> +	u8 resp_buf[MAX_RESPONSE_SIZE];
> +	struct tee_context *ctx;
> +	struct tee_shm *shm;
> +};
> +
> +/*
> + * Note: ftpm_tee_tpm_op_recv and ftpm_tee_tpm_op_send are called from the
> + * same routine tpm_try_transmit in tpm-interface.c. These calls are protected
> + * by chip->tpm_mutex => There is no need for protecting any data shared
> + * between these routines ex: struct ftpm_tee_private
> + */

This comment should be removed.

> +
> +#endif /* __TPM_FTPM_TEE_H__ */
> -- 
> 2.19.1
> 

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

/Jarkko