[anonym29]

ARM has the exact same problem via TrustZone. Different technical implementation, slightly different known capabilities, but fundamentally, still an unauditable, unremovable ring -3 subsystem that cannot be controlled by the legitimate, lawful owner of the hardware.

[M95D]

It depends on the CPU. For Rockchip we have open source BL31 blob [1] and it's supported by mainline u-boot.

And I think it's ring -2, because it's not a separate CPU.

[1] https://www.collabora.com/news-and-blog/blog/2024/02/21/almo...