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I am reading about ARM Trustzone at this link. I understand that using TrustZone, one can partition the memory into secure and non-secure regions. Vendors may use this to run a secure OS.

What I am curious about is that what is the granularity support for this partition ? Is it just that there can be a block of memory marked "secure" and there can be only one such block of memory per OS ? Does TrustZone have the capacity to partition memory for individual processes ?

Lets say I have a .so file (hypothetical example) for a Linux application. Could it be possible that the same code in process A could be marked secure in virtual address 0x1000 to 0x2000, while in process B could be marked secure in virtual address 0x5000 to 0x6000 ?

Jake
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1 Answers1

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TrustZone partitioning happens at the physical memory level, so the process-level parts of your question don't really apply. Note that Linux as the non-secure OS can't even see secure memory, so having virtual mappings for inaccessible addresses would be of little use; however the secure OS does have the ability to map both secure and non-secure physical addresses by virtue of the NS bit in its page table entries.

As for how that physical partitioning goes, it depends on the implementation. The TZC-380 your link refers to supports 2-16 regions with a minimum 32KB granularity; its successor the TZC-400 has 9 regions, and goes all the way down to 4KB granularity. Other implementations may be different still, although granularity below 4KB is unlikely since that would be pretty much unusable for the CPU with its MMU on. Also, there are usually some things in a system which are going to be hardwired to the secure memory map only (the TZC's programming interface, for one), and that often includes some dedicated secure SRAM.

Notlikethat
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