commit d82afbfaa839f2d4b86b883fc570f4955a9bec0e
author George Beckstein <becksteing@embeddedplanet.com> Thu Oct 29 17:32:11 2020 -0400
committer Fabio Utzig <utzig@utzig.org> Tue Nov 03 19:16:46 2020 -0300
tree 23996ffee54e2463760cc713a87171db6f3dbb61
parent ea30ef3ca7f6e96cc8c99bfa83a012323003cee5

Mbed-OS porting layer implementation for mcuboot

This PR provides a porting layer implementation and framework for building an mcuboot-based bootloader with Mbed-OS. Some symbols are not provided by the Mbed-OS port within mcuboot, namely:

- The secondary storage device (see below)
- The signing keys
- The encryption keys, if used

Use of this port is demonstrated by the following projects:
- https://github.com/AGlass0fMilk/mbed-mcuboot-demo (a complete mcuboot/Mbed-OS-based bootloader)
- https://github.com/AGlass0fMilk/mbed-mcuboot-blinky (example showing how to make an Mbed-OS application that is bootable by mcuboot)

Memory porting implementation:

The underlying implemenation uses Mbed's BlockDevice API as the storage backend for mcuboot's memory operations. This provides a very flexible way of configuring the location and layout of the secondary flash storage area. To build an mcuboot-based bootloader with Mbed-OS, the user must implement a hook function, mbed::BlockDevice* get_secondary_bd(), to provide the secondary BlockDevice that mcuboot will use.

The signing and encryption keys must also be provided by the user. They can be generated using the existing imgtool utility in the same manner used by Zephyr. There are no automated build steps currently provided by Mbed-OS to sign/encrypt build artifacts.

Known limitations:

The update candidate encryption features have not yet been fully tested. A truly secure implementation will require integration with Mbed's TRNG API in the future to inhibit side-channel attacks on the decryption process.

The TinyCrypt backend is currently only supported for Mbed-OS builds when building with the GCC toolchain. The new cmake-based Mbed-OS build system will fix the underlying issue (file name uniqueness).

Signed-off-by: George Beckstein <becksteing@embeddedplanet.com>
Signed-off-by: Evelyne Donnaes <evelyne.donnaes@arm.com>
Signed-off-by: Lingkai Dong <lingkai.dong@arm.com>

Co-authored-by: Lingkai Dong <lingkai.dong@arm.com>
Co-authored-by: Fabio Utzig <fabio.utzig@nordicsemi.no>