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-implement... .

As well as reference code for the firmware available here: https://github.com/Microsoft/ms-tpm-20-ref/tree/master/Samples/ARM32-Firmwar...

Tested-by: Thirupathaiah Annapureddy thiruan@microsoft.com Signed-off-by: Thirupathaiah Annapureddy thiruan@microsoft.com Co-authored-by: Sasha Levin sashal@kernel.org 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 | 350 ++++++++++++++++++++++++++++++++ drivers/char/tpm/tpm_ftpm_tee.h | 40 ++++ 4 files changed, 396 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 88a3c06fc153..17bfbf9f572f 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 && OPTEE + ---help--- + This driver proxies for firmware TPM 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..74766a4d3280 --- /dev/null +++ b/drivers/char/tpm/tpm_ftpm_tee.c @@ -0,0 +1,350 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) Microsoft Corporation + * + * Implements a firmware TPM as described here: + * https://www.microsoft.com/en-us/research/publication/ftpm-software-implement... + * + * A reference implementation is available here: + * https://github.com/microsoft/ms-tpm-20-ref/tree/master/Samples/ARM32-Firmwar... + */ + +#include <linux/acpi.h> +#include <linux/of.h> +#include <linux/of_platform.h> +#include <linux/platform_device.h> +#include <linux/tee_drv.h> +#include <linux/tpm.h> +#include <linux/uuid.h> + +#include "tpm.h" +#include "tpm_ftpm_tee.h" + +/* + * TA_FTPM_UUID: BC50D971-D4C9-42C4-82CB-343FB7F37896 + * + * Randomly generated, and must correspond to the GUID on the TA side. + * Defined here in the reference implementation: + * https://github.com/microsoft/ms-tpm-20-ref/blob/master/Samples/ARM32-Firmwar... + */ +static const uuid_t ftpm_ta_uuid = + UUID_INIT(0xBC50D971, 0xD4C9, 0x42C4, + 0x82, 0xCB, 0x34, 0x3F, 0xB7, 0xF3, 0x78, 0x96); + +/** + * ftpm_tee_tpm_op_recv - retrieve fTPM response. + * @chip: the tpm_chip description as specified in driver/char/tpm/tpm.h. + * @buf: the buffer to store data. + * @count: the number of bytes to read. + * + * Return: + * In case of success the number of bytes received. + * On failure, -errno. + */ +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. + * @chip: the tpm_chip description as specified in driver/char/tpm/tpm.h + * @buf: the buffer to send. + * @len: the number of bytes to send. + * + * Return: + * In case of success, returns 0. + * On failure, -errno + */ +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; +} + +/** + * ftpm_tee_probe - initialize the fTPM + * @pdev: the platform_device description. + * + * Return: + * On success, 0. On failure, -errno. + */ +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)) { + if (ERR_PTR(pvt_data->ctx) == -ENOENT) + return -EPROBE_DEFER; + dev_err(dev, "%s: tee_client_open_context failed\n", __func__); + return ERR_PTR(pvt_data->ctx); + } + + /* 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 + * @pdev: the platform_device description. + * + * Return: + * 0 always. + */ +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 = "ftpm-tee", + .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..f98daa7bf68c --- /dev/null +++ b/drivers/char/tpm/tpm_ftpm_tee.h @@ -0,0 +1,40 @@ +/* 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/tpm.h> +#include <linux/uuid.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; +}; + +#endif /* __TPM_FTPM_TEE_H__ */

This patch adds basic documentation to describe the new fTPM driver.

Signed-off-by: Sasha Levin sashal@kernel.org --- Documentation/security/tpm/index.rst | 1 + Documentation/security/tpm/tpm_ftpm_tee.rst | 27 +++++++++++++++++++++ 2 files changed, 28 insertions(+) create mode 100644 Documentation/security/tpm/tpm_ftpm_tee.rst

diff --git a/Documentation/security/tpm/index.rst b/Documentation/security/tpm/index.rst index af77a7bbb070..15783668644f 100644 --- a/Documentation/security/tpm/index.rst +++ b/Documentation/security/tpm/index.rst @@ -4,4 +4,5 @@ Trusted Platform Module documentation

.. toctree::

+ tpm_ftpm_tee tpm_vtpm_proxy diff --git a/Documentation/security/tpm/tpm_ftpm_tee.rst b/Documentation/security/tpm/tpm_ftpm_tee.rst new file mode 100644 index 000000000000..8c2bae16e3d9 --- /dev/null +++ b/Documentation/security/tpm/tpm_ftpm_tee.rst @@ -0,0 +1,27 @@ +============================================= +Firmware TPM Driver +============================================= + +This document describes the firmware Trusted Platform Module (fTPM) +device driver. + +Introduction +============ + +This driver is a shim for firmware implemented in ARM's TrustZone +environment. The driver allows programs to interact with the TPM in the same +way they would interact with a hardware TPM. + +Design +====== + +The driver acts as a thin layer that passes commands to and from a TPM +implemented in firmware. The driver itself doesn't contain much logic and is +used more like a dumb pipe between firmware and kernel/userspace. + +The firmware itself is based on the following paper: +https://www.microsoft.com/en-us/research/wp-content/uploads/2017/06/ftpm1.pd... + +When the driver is loaded it will expose ``/dev/tpmX`` character devices to +userspace which will enable userspace to communicate with the firmware TPM +through this device.