88 lines
3.4 KiB
ReStructuredText
88 lines
3.4 KiB
ReStructuredText
Trusted Firmware-M Integration
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##############################
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The Trusted Firmware-M (TF-M) section contains information about the
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integration between TF-M and Zephyr RTOS. Use this information to help
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understand how to integrate TF-M with Zephyr for Cortex-M platforms and make
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use of its secure run-time services in Zephyr applications.
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Board Definitions
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*****************
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TF-M will be built for the secure processing environment along with Zephyr if
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the :kconfig:option:`CONFIG_BUILD_WITH_TFM` flag is set to ``y``.
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Generally, this value should never be set at the application level, however,
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and all config flags required for TF-M should be set in a board variant with
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the ``_ns`` suffix.
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This board variant must define an appropriate flash, SRAM and peripheral
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configuration that takes into account the initialisation process in the secure
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processing environment. :kconfig:option:`CONFIG_TFM_BOARD` must also be set via
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`modules/trusted-firmware-m/Kconfig.tfm <https://github.com/zephyrproject-rtos/zephyr/blob/main/modules/trusted-firmware-m/Kconfig.tfm>`__
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to the board name that TF-M expects for this target, so that it knows which
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target to build for the secure processing environment.
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Example: ``mps2_an521_ns``
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==========================
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The ``mps2_an521`` target is a dual-core Arm Cortex-M33 evaluation board that,
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when using the default board variant, would generate a secure Zephyr binary.
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The optional ``mps2_an521_ns`` target, however, sets these additional
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kconfig flags that indicate that Zephyr should be built as a
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non-secure image, linked with TF-M as an external project, and optionally the
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secure bootloader:
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* :kconfig:option:`CONFIG_TRUSTED_EXECUTION_NONSECURE` ``y``
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* :kconfig:option:`CONFIG_ARM_TRUSTZONE_M` ``y``
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Comparing the ``mps2_an521.dts`` and ``mps2_an521_ns.dts`` files, we can see
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that the ``_ns`` version defines offsets in flash and SRAM memory, which leave
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the required space for TF-M and the secure bootloader:
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::
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reserved-memory {
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#address-cells = <1>;
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#size-cells = <1>;
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ranges;
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/* The memory regions defined below must match what the TF-M
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* project has defined for that board - a single image boot is
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* assumed. Please see the memory layout in:
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* https://git.trustedfirmware.org/TF-M/trusted-firmware-m.git/tree/platform/ext/target/mps2/an521/partition/flash_layout.h
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*/
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code: memory@100000 {
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reg = <0x00100000 DT_SIZE_K(512)>;
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};
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ram: memory@28100000 {
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reg = <0x28100000 DT_SIZE_M(1)>;
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};
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};
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This reserves 1 MB of code memory and 1 MB of RAM for secure boot and TF-M,
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such that our non-secure Zephyr application code will start at 0x10000, with
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RAM at 0x28100000. 512 KB code memory is available for the NS zephyr image,
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along with 1 MB of RAM.
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This matches the flash memory layout we see in ``flash_layout.h`` in TF-M:
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::
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* 0x0000_0000 BL2 - MCUBoot (0.5 MB)
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* 0x0008_0000 Secure image primary slot (0.5 MB)
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* 0x0010_0000 Non-secure image primary slot (0.5 MB)
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* 0x0018_0000 Secure image secondary slot (0.5 MB)
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* 0x0020_0000 Non-secure image secondary slot (0.5 MB)
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* 0x0028_0000 Scratch area (0.5 MB)
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* 0x0030_0000 Protected Storage Area (20 KB)
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* 0x0030_5000 Internal Trusted Storage Area (16 KB)
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* 0x0030_9000 NV counters area (4 KB)
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* 0x0030_A000 Unused (984 KB)
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``mps2/an521`` will be passed in to Tf-M as the board target, specified via
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:kconfig:option:`CONFIG_TFM_BOARD`.
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