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TrustZone MMU Validation

Note: This was originally posted on 19th July 2013 at http://forums.arm.com

I am running code in Secure Mode on a Cortex-A9 platform. The MMU registers within the CP15 are bank switched when secure mode is entered. Is it possible to read READ the normal world TTBR0/1 and TTBCR registers. What is involved in doing this?

Scott Cloutier over 12 years ago

Note: This was originally posted on 19th July 2013 at http://forums.arm.com

Looks to have done the trick! Thanks!
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Peter Harris over 12 years ago

Note: This was originally posted on 19th July 2013 at http://forums.arm.com

Switch into monitor mode
Disable interrupts,
Write NS=1 into the CP15 operation to access the normal world copy of the banked registers
Read values from TTBR/TTBCR into registers
Set NS=0, re-enable interrupts
Return out of monitor mode.

Basically you need NS=1 to access the banked state, and the only place you can do this without changing into the Normal world execution is in monitor mode. The rest of the faffing about with interrupts is just to make this safe.

HTH,
Iso
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