Это не у STM32, это у Cortex-M3/4 вообще. The Cortex-M4 processor implements a local exclusive monitor. The local monitor within the processor has been constructed so that it does not hold any physical address, but instead treats any access as matching the address of the previous LDREX. This means that the implemented exclusives reservation granule is the entire memory address range.
https://developer.arm.com/documentation/100166/0001/Programmers-Model/Exclusive-monitor