[pedroaraujo]

TrustZone is an addon that can be used to implement actual security features into a certain device.

It is not attached to ARM's CPUs, not it is mandatory, it is just something that SoC developers can pick up and implement however they want.

[cyphar]

Are there examples of non-TrustZone ARM SoCs? I'm not aware of any, which would make it a moot point about whether a theoretical vendor could make the decision to not includ eit.

[suihkulokki]

The hikey and hikey960 devboards let you build your own code to run in the trustzone - eg the boot chain isn't signed and secure. The trustzone and uefi implemention these boards use is also fully open source.

[qb45]

Maybe we should start with stating that the core of TZ is an execution mode of the ARM CPU privileged above the normal kernel mode, not a separate core running some obscure code. TZ can run any suitable hypervisor or just be left unused. It's nothing like the ME/PSP.

Still, some boards/devices may lock it down, for example by code signing.

[monocasa]

I think it gets obfuscated due to the fact that about the only public information that AMD provides on the PSP is that it uses ARM Trustzone technology.

[bryanbuckley]

Most likely the best you'll get is either a fully usable TrustZone SoC (so you can have your bootloader or linux do what you want) or there are SKUs of SoC where the ROM locks the various TZ registers into certain configurations which is meant to disable any runtime usage of the TZ by higher level SW e.g. bootloader or OS.

If you are making something with the SoC.. it's probably safer to buy the locked down version of the SoC than to mess about with TZ or to leave it open.

[pedroaraujo]

An ARM CPU is hardly comparable to an Intel/AMD CPU. And I don't mean in terms of performance.

The CPUs from Intel/AMD are much more than a simple CPU, they are a complete system on a chip with a lot of more features that go beyond processing power for your system. On the other hand, an ARM CPU is just a simple CPU.

If you want to make comparisons, a more correct one would be between the Intel/AMD CPUs and a Snapdragon processor.

[monocasa]

ARM chips have been full SoCs for far longer than x86 chips have been. It took a while for Intel and AMD to integrate the memory controllers and PCI root complex onto the CPU rather than in the northbridge.

AKAIK, only the Versatile/RealView style boards that an SoC manufacturer would get directly from ARM come with bare ARM chips. Anything other than that is an SoC.

[pedroaraujo]

ARM doesn't design SoCs, ARM designs CPUs.

My point is that an Intel/AMD product is a complete solution while an ARM product is just the very basic implementation of a CPU.

ARM doesn't mandate on anything related to the SoC except for the CPU, everything else related to PCI buses, memories, physical implementation, chipsets, etc, is up to the SoC developer to decide and implement.