This patch introduces the ram-load mode in addition to the other
upgrade modes (swap strategies, overwrite-only, direct-XIP). When
ram-load is enabled with the MCUBOOT_RAM_LOAD option, mcuboot
selects the newest valid image based on the image version numbers from
the image header, thereafter the selected image loaded to the RAM and
executed from there. Load address is extracted from the image header.
Therefore the images must be linked to the RAM memory region.
The ram-load mode is very similar to the direct-XIP mode, main
difference is to load the newest image to the RAM beforehand the
authentication and execution. Similar to direct-XIP mode either
of the primary and the secondary slots can hold the active image.
Ram-load can be useful in case of a bit more powerful SoC, which
is not constrained in terms of internal RAM. It could be that image
is stored in external and therefore untrusted flash. Loading image
to internal (trusted) RAM is essential from the security point
of view the system. Furthermore execution from internal RAM is much
faster than from external flash.
This patch is based on the RAM_LOADING upgrade strategy which was
first introduced in the Trusted Firmware-M project.
Source TF-M version: TF-Mv1.0.
Change-Id: I95f02ff07c1dee51244ac372284f449c2efab362
Signed-off-by: Tamas Ban <tamas.ban@arm.com>
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