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What is the relationship between the region defined by SAU/IDAU and the region exempt from memory attribution?

Information in this article applies to:

  • ARMv8-M

Problem/Question

What is the relationship between the region defined by SAU/IDAU and the region exempt from memory attribution?

Scenario

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Answer

Both the Security Attribution Unit (SAU) and the Implementation Defined Attribution Unit (IDAU) can provide memory security attribution. The final memory security attribution is determined by the stricter security attribution, either specified by the SAU or by the IDAU. For example, if the IDAU specifies attributes with a higher security, the IDAU attributes override the SAU attributes. However, this security attribution rule does not apply to the following range or regions:

  • The architecturally defined ranges that are exempt from memory attribution.

  • The IDAU-defined regions that are exempt from memory attribution.

If the IDAUNCHKA or IDAUNCHKB signal is HIGH, the address associated with the IDAU region is not subject to attribution or security checks. The security attribution is determined only by one of the following conditions. This behavior is independent of any security attribution associated with the address in the processor SAU or presented on the IDAU interface.

  • The processor security state for software reads and writes to the address.

  • The HNONSECD input signal on D-AHB and DHCSR.S_SDE for debug accesses.

Workaround

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Example

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Related Information

For details about the architecturally defined regions exempt from memory attribution, see the section that describes Security attribution in the Armv8-M architecture reference manual.

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