It would be interesting to know what the ARM SecurCore SC300 processor[1] does, if that is constant time multiply or if they just expect you will use the hardware crypto accelerators that are commonly integrated with it, e.g. in the ST33 [2].

[1] https://developer.arm.com/ip-products/processors/securcore/s... [2] https://www.st.com/en/secure-mcus/st33-arm-sc300.html