Hardware Abstraction Layer

Organization: Arm Limited
Contact: tf-m@lists.trustedfirmware.org
API Version: 0.9

Introduction

TF-M HAL abstracts the hardware-oriented and platform specific operations on the SPE side and provides a set of APIs to the upper layers such as SPM, RoT Service. The HAL aims to cover the platform different aspects whereas common architecturally defined aspects are done generically within the common SPE. In some cases, although the operations are defined architecturally, it may not be possible to generalize implementations because lots of information is only known to platforms. It is more efficient to define a HAL API for those architectural operations as well.

Note

TBSA-M provides the hardware requirements for security purposes. TF-M HAL tries to reference TBSA-M recommendations in the interfaces from the software perspective only. Please reference TBSA-M for your security hardware design.

Design Goals

TF-M HAL is designed to simplify the integration efforts on different platforms.

TF-M HAL is designed to make it easy to use the hardware and develop the SPM and RoT Service which need to access the devices.

TF-M HAL is designed to make the structure clearer and let the TF-M mainly focus on PSA implementation.

Overview

This section provides an overview of the abstraction layer structure.

Here lists a minimal set of necessary functionalities:

Isolation API: Provides the necessary isolation functionalities required by the PSA-FF-M and TBSA-M, and provides APIs to SPM to check the permissions of memory access.

Platform API: Provides the platform initialization, platform-specific memory information, system reset, etc.

Log dev API: Provides the log system functions.

Interrupt API: Provides the interrupt functions.

Note

There is a non-secure HAL that focuses on the mailbox operation API for Dual-core topology. For more information about it, please refer to Mailbox Design in TF-M on Dual-core System.
The minimal set of TF-M HAL is sufficient for Secure Partitions by using customized peripheral interfaces. To provide easier portability for the Secure Partitions, a Secure Partition HAL is provided in this design too.
The debug mechanisms give the external entity the corresponding right to access the system assets. TF-M ensures that the external entity is permitted access to those assets. Currently, TF-M only needs the debug authentication. The whole debug mechanism and related HAL will be enhanced in the future. Please refer to the Debug authentication settings section for more detail.

Design Principles

As TF-M runs on resource-constrained devices, the HAL tries to avoid multiple level abstractions which cost more resources.

Part of the HAL interfaces does not focus on exact hardware operations such as power on/off or PIN manipulation. Instead, the HAL abstracts higher-level interfaces to reserve the implementation flexibility for the platform vendors.

The TF-M HAL should be easy to deprecate APIs and provide compatibilities. Any API incompatibility should be detected during building.

TF-M relies on the HAL APIs to be implemented correctly and trusts the HAL APIs. TFM can provide assertions to detect common programming errors but essentially no further extensive checks will be provided.

Source Files

This section describes the source file of the TF-M HAL, including the header and c files.

tfm_hal_defs.h

This header file contains the definitions of common macros and types used by all HAL APIs. Please refer to Status Codes for detailed definitions.

tfm_hal_[module].[h/c]

All other headers and c files are classified by the modules, such as isolation, platform, interrupt, devices, etc.

Note

There are common files in the platform folder include the implemented HAL APIs. The platform vendors can use them directly but need to implement all the sub APIs.

Status Codes

These are common status and error codes for all HAL APIs.

Types

tfm_hal_status_t

This is a status code to be used as the return type of HAL APIs.

enum tfm_hal_status_t {
    TFM_HAL_ERROR_MEM_FAULT = SCHAR_MIN,
    TFM_HAL_ERROR_MAX_VALUE,
    TFM_HAL_ERROR_BAD_STATE,
    TFM_HAL_ERROR_NOT_SUPPORTED,
    TFM_HAL_ERROR_INVALID_INPUT,
    TFM_HAL_ERROR_NOT_INIT,
    TFM_HAL_ERROR_GENERIC,
    TFM_HAL_SUCCESS = 0
};

Error Codes

Negative values indicate an error. Zero and positive values indicate success.

Here is the general list. The detailed usages for each error code are described in the API introduction sections.

TFM_HAL_SUCCESS

Status code to indicate general success.

TFM_HAL_ERROR_GENERIC

Status code to indicate an error that does not correspond to any defined failure cause.

TFM_HAL_ERROR_NOT_INIT

Status code to indicate that the module is not initialed.

TFM_HAL_ERROR_INVALID_INPUT

Status code to indicate that the input is invalid.

TFM_HAL_ERROR_NOT_SUPPORTED

Status code to indicate that the requested operation or a parameter is not supported.

TFM_HAL_ERROR_BAD_STATE

Status code to indicate that the requested action cannot be performed in the current state.

TFM_HAL_ERROR_MAX_VALUE

Status code to indicate that the current number has got the max value.

TFM_HAL_ERROR_MEM_FAULT

Status code to indicate that the memory check failed.

API Definition for TF-M SPM

This section describes the APIs defined for TF-M SPM.

Platform API

The platform API is a higher-level abstraction layer of the platform, other than a dedicated API set for the special hardware devices.

APIs

tfm_hal_platform_init()

Prototype

enum tfm_hal_status_t tfm_hal_platform_init(void)

Description

This API performs the platform initializations before the SPM initialization.

The initializations could include but not limited to: - Fault handlers - Reset configurations - Debug init - NVIC init

Parameter

void - None.

Return Values

TFM_HAL_SUCCESS - Init success.
TFM_HAL_ERROR_GENERIC - Generic errors.

tfm_hal_system_reset()

Prototype

void tfm_hal_system_reset(void)

Description

This API performs a system reset.

The platform can uninitialize some resources before reset.

Parameter

void - None

Return Values

void - None

Note

This API should not return.

Isolation API

The PSA-FF-M defines three isolation levels and a memory access rule to provide diverse levels of securitiy. The isolation API provides the functions to implement these requirements.

Memory Access Attributes

The memory access attributes are encoded as bit fields, you can logic OR them to have a combination of the atrributes, for example TFM_HAL_ACCESS_UNPRIVILEGED | TFM_HAL_ACCESS_READABLE is unprivileged readable. The data type is uint32_t.

TFM_HAL_ACCESS_EXECUTABLE

The memory is executable.

#define TFM_HAL_ACCESS_EXECUTABLE (1UL << 0)

TFM_HAL_ACCESS_READABLE

The memory is readable.

#define TFM_HAL_ACCESS_READABLE (1UL << 1)

TFM_HAL_ACCESS_WRITABLE

The memory is writable.

#define TFM_HAL_ACCESS_WRITABLE (1UL << 2)

TFM_HAL_ACCESS_UNPRIVILEGED

The memory is unprivileged mode accessible.

#define TFM_HAL_ACCESS_UNPRIVILEGED (1UL << 3)

TFM_HAL_ACCESS_DEVICE

The memory is a MMIO device.

#define TFM_HAL_ACCESS_DEVICE (1UL << 4)

TFM_HAL_ACCESS_NS

The memory is accessible from NSPE

#define TFM_HAL_ACCESS_NS (1UL << 5)

APIs

tfm_hal_set_up_static_boundaries()

Prototype

enum tfm_hal_status_t tfm_hal_set_up_static_boundaries(void)

Description

This API sets up the static isolation boundaries which are constant throughout the runtime of the system.

The boundaries include:

The SPE boundary between the SPE and the NSPE
The PSA RoT isolation boundary between the PSA Root of Trust and the Application Root of Trust which is for isolation level 2 and 3 only.

Please refer to the PSA-FF-M for the definitions of the isolation boundaries.

Return Values

TFM_HAL_SUCCESS - the isolation boundaries have been set up.
TFM_HAL_ERROR_GENERIC - failed to set up the isolation boundaries.

tfm_hal_update_boundaries()

Prototype

enum tfm_hal_status_t tfm_hal_update_boundaries(
                            const struct partition_load_info_t *p_ldinf,
                            void *p_boundaries);

Description

This API updates the partition isolation boundary for isolation level 2 and 3. The isolation boundary includes the thread privilege and the partition private data. In isolation level 2, the SPM only updates the partition thread privilege. In isolation level 3, the SPM updates the partition thread privilege, and protects each partition’s private data.

The access permissions outside the boundary is platform-dependent.

Parameter

p_ldinf - Partition load information.
p_boundaries - Platform boundary handle for the partition.

Return Values

TFM_HAL_SUCCESS - the isolation boundary has been set up.
TFM_HAL_ERROR_GENERIC - failed to set upthe isolation boundary.

Note

This API is only for platforms using MPU as isolation hardwares. A generic API for all platforms will be introduced in future versions.

tfm_hal_memory_has_access()

Prototype

tfm_hal_status_t tfm_hal_memory_has_access(const uintptr_t base,
                                           size_t size,
                                           uint32_t attr)

Description

This API checks if the memory region defined by base and size has the given access atrributes - attr.

The Attributes include NSPE access, privileged mode, and read-write permissions.

Parameter

base - The base address of the region.
size - The size of the region.
attr - The Memory Access Attributes.

Return Values

TFM_HAL_SUCCESS - The memory region has the access permissions.
TFM_HAL_ERROR_MEM_FAULT - The memory region does not have the access permissions.
TFM_HAL_ERROR_INVALID_INPUT - Invalid inputs.
TFM_HAL_ERROR_GENERIC - An error occurred.

tfm_hal_bind_boundaries()

Prototype

enum tfm_hal_status_t tfm_hal_bind_boundaries(
                                  const struct partition_load_info_t *p_ldinf,
                                  void **pp_boundaries);

Description

This API binds partition with the platform via a boundary handle.

Parameter

p_ldinf - Partition load information.
pp_boundaries - Pointer of a the partition’s platform boundary handle.

Return Values

TFM_HAL_SUCCESS - the handle has been binded successfully.
TFM_HAL_ERROR_GENERIC - failed to bind the handle.

Note

The platform maintains the platform-specific settings for SPM further usage, such as updating partition hardware boundaries or checking resource accessibility. The platform needs to manage the settings with an internal mechanism, and returns a handle to SPM. SPM delivers this handle back to platform when necessary. And SPM checks this handle to decide if the platform-specific settings need to be updated. Hence multiple partitions can have the same handle if they have the same platform-specific settings.

Log API

The log API is used by the TF-M log system. The log device could be uart, memory, usb, etc.

APIs

tfm_hal_output_partition_log()

Prototype

int32_t tfm_hal_output_partition_log(const unsigned char *str, uint32_t len)

Description

This API is called by Secure Partition to output logs.

Parameter

str - The string to output.
len - Length of the string in bytes.

Return Values

Positive values - Number of bytes output.
TFM_HAL_ERROR_NOT_INIT - The log device has not been initialized.
TFM_HAL_ERROR_INVALID_INPUT - Invalid inputs when str is NULL or len is zero.

Note

None.

tfm_hal_output_spm_log()

Prototype

int32_t tfm_hal_output_spm_log(const unsigned char *str, uint32_t len)

Description

This API is called by SPM to output logs.

Parameter

str - The string to output.
len - Length of the string in bytes.

Return Values

Positive numbers - Number of bytes output.
TFM_HAL_ERROR_NOT_INIT - The log device has not been initialized.
TFM_HAL_ERROR_INVALID_INPUT - Invalid inputs when str is NULL or len is zero.

Note

Please check TF-M log system for more information.

Interrupt APIs

The SPM HAL interrupt APIs are intended for operations on Interrupt Controllers of platforms.

APIs for control registers of interrupt sources are not in the scope of this set of APIs. Secure Partitions should define the APIs for managing interrupts with those MMIO registers.

APIs

tfm_hal_irq_enable()

Prototype

enum tfm_hal_status_t tfm_hal_irq_enable(uint32_t irq_num)

Description

This API enables an interrupt from the Interrupt Controller of the platform.

Parameter

irq_num - the interrupt to be enabled with a number

Return Values

TFM_HAL_ERROR_INVALID_INPUT - the irq_num exceeds The maximum
supported number of external interrupts.
TFM_HAL_ERROR_GENERIC - failed to enable the interrupt.
TFM_HAL_SUCCESS - the interrupt is successfully enabled.

tfm_hal_irq_disable()

Prototype

enum tfm_hal_status_t tfm_hal_irq_disable(uint32_t irq_num)

Description

This API disables an interrupt from the Interrupt Controller of the platform.

Parameter

irq_num - the interrupt to be disabled with a number

Return Values

TFM_HAL_ERROR_INVALID_INPUT - the irq_num exceeds The maximum
supported number of external interrupts.
TFM_HAL_ERROR_GENERIC - failed to disable the interrupt.
TFM_HAL_SUCCESS - the interrupt is successfully disabled.

tfm_hal_irq_clear_pending()

Prototype

enum tfm_hal_status_t tfm_hal_irq_clear_pending(uint32_t irq_num)

Description

This API clears an active and pending interrupt.

Parameter

irq_num - the interrupt to be disabled with a number

Return Values

TFM_HAL_ERROR_INVALID_INPUT - the irq_num exceeds The maximum
supported number of external interrupts.
TFM_HAL_ERROR_GENERIC - failed to clear the pending interrupt.
TFM_HAL_SUCCESS - the pending interrupt has been cleared.

Initializations

Prototype

enum tfm_hal_status_t {source_symbol}_init(void *p_pt,
                                           struct irq_load_info_t *p_ildi)

The {source_symbol} is:

irq_{source}, if the source attribute of the IRQ in Partition manifest is a number
Lowercase of source attribute, if source is a symbolic name

Description

Each interrupt has an initialization function individually. The SPM calls the functions while loading the Partitions.

The following initializations are required for each interrupt:

Setting the priority. The value must between 0 to 0x80 exclusively.
Ensuring that the interrupt targets the Secure State.
Saving the input parameters for future use.

Platforms can have extra initializations as well.

Parameter

p_pt - pointer to Partition runtime struct of the owner Partition
p_ildi - pointer to irq_load_info_t struct of the interrupt

Note

Please refer to the :doc: IRQ intergration guide<tfm_secure_irq_integration_guide> for more information.

API Definition for Secure Partitions

The Secure Partition (SP) HAL mainly focuses on two parts:

Peripheral devices. The peripherals accessed by the TF-M default Secure Partitions.

Secure Partition abstraction support. The Secure Partition data that must be provided by the platform.

The Secure Partition abstraction support will be introduced in the peripheral API definition.

ITS and PS flash API

There are two kinds of flash:

Internal flash. Accessed by the PSA Internal Trusted Storage (ITS) service.

External flash. Accessed by the PSA Protected Storage (PS) service.

The ITS HAL for the internal flash device is defined in the tfm_hal_its.h header and the PS HAL in the tfm_hal_ps.h header.

Macros

Internal Trusted Storage

TFM_HAL_ITS_FLASH_DRIVER

Defines the identifier of the CMSIS Flash ARM_DRIVER_FLASH object to use for ITS. It must have been allocated by the platform and will be declared extern in the HAL header.

TFM_HAL_ITS_PROGRAM_UNIT

Defines the size of the ITS flash device’s physical program unit (the smallest unit of data that can be individually programmed to flash). It must be equal to TFM_HAL_ITS_FLASH_DRIVER.GetInfo()->program_unit, but made available at compile time so that filesystem structures can be statically sized.

TFM_HAL_ITS_FLASH_AREA_ADDR

Defines the base address of the dedicated flash area for ITS.

TFM_HAL_ITS_FLASH_AREA_SIZE

Defines the size of the dedicated flash area for ITS in bytes.

TFM_HAL_ITS_SECTORS_PER_BLOCK

Defines the number of contiguous physical flash erase sectors that form a logical filesystem erase block.

Protected Storage

TFM_HAL_PS_FLASH_DRIVER

Defines the identifier of the CMSIS Flash ARM_DRIVER_FLASH object to use for PS. It must have been allocated by the platform and will be declared extern in the HAL header.

TFM_HAL_PS_PROGRAM_UNIT

Defines the size of the PS flash device’s physical program unit (the smallest unit of data that can be individually programmed to flash). It must be equal to TFM_HAL_PS_FLASH_DRIVER.GetInfo()->program_unit, but made available at compile time so that filesystem structures can be statically sized.

TFM_HAL_PS_FLASH_AREA_ADDR

Defines the base address of the dedicated flash area for PS.

TFM_HAL_PS_FLASH_AREA_SIZE

Defines the size of the dedicated flash area for PS in bytes.

TFM_HAL_PS_SECTORS_PER_BLOCK

Defines the number of contiguous physical flash erase sectors that form a logical filesystem erase block.

Optional definitions

The TFM_HAL_ITS_FLASH_AREA_ADDR, TFM_HAL_ITS_FLASH_AREA_SIZE and TFM_HAL_ITS_SECTORS_PER_BLOCK definitions are optional. If not defined, the platform must implement tfm_hal_its_fs_info() instead.

Equivalently, tfm_hal_its_ps_info() must be implemented by the platform if TFM_HAL_ITS_FLASH_AREA_ADDR, TFM_HAL_ITS_FLASH_AREA_SIZE or TFM_HAL_ITS_SECTORS_PER_BLOCK is not defined.

Objects

ARM_DRIVER_FLASH

The ITS and PS HAL headers each expose a CMSIS Flash Driver instance.

extern ARM_DRIVER_FLASH TFM_HAL_ITS_FLASH_DRIVER

extern ARM_DRIVER_FLASH TFM_HAL_PS_FLASH_DRIVER

The CMSIS Flash Driver provides the flash primitives ReadData(), ProgramData() and EraseSector() as well as GetInfo() to access flash device properties such as the sector size.

Types

tfm_hal_its_fs_info_t

Struct containing information required from the platform at runtime to configure the ITS filesystem.

struct tfm_hal_its_fs_info_t {
    uint32_t flash_area_addr;
    size_t flash_area_size;
    uint8_t sectors_per_block;
};

Each attribute is described below:

flash_area_addr - Location of the block of flash to use for ITS

flash_area_size - Number of bytes of flash to use for ITS

sectors_per_block - Number of erase sectors per logical FS block

tfm_hal_ps_fs_info_t

Struct containing information required from the platform at runtime to configure the PS filesystem.

struct tfm_hal_ps_fs_info_t {
    uint32_t flash_area_addr;
    size_t flash_area_size;
    uint8_t sectors_per_block;
};

Each attribute is described below:

flash_area_addr - Location of the block of flash to use for PS

flash_area_size - Number of bytes of flash to use for PS

sectors_per_block - Number of erase sectors per logical FS block

Functions

tfm_hal_its_fs_info()

Prototype

enum tfm_hal_status_t tfm_hal_its_fs_info(struct tfm_hal_its_fs_info_t *fs_info);

Description

Retrieves the filesystem configuration parameters for ITS.

Parameter

fs_info - Filesystem config information

Return values

TFM_HAL_SUCCESS - The operation completed successfully
TFM_HAL_ERROR_INVALID_INPUT - Invalid parameter

Note

This function should ensure that the values returned do not result in a security compromise. The block of flash supplied must meet the security requirements of Internal Trusted Storage.

tfm_hal_ps_fs_info()

Prototype

enum tfm_hal_status_t tfm_hal_ps_fs_info(struct tfm_hal_ps_fs_info_t *fs_info);

Description

Retrieves the filesystem configuration parameters for PS.

Parameter

fs_info - Filesystem config information

Return values

TFM_HAL_SUCCESS - The operation completed successfully
TFM_HAL_ERROR_INVALID_INPUT - Invalid parameter

Note

This function should ensure that the values returned do not result in a security compromise.