Only if there is a data race - if there is no data race C++ lets you do it. Rust doesn't let you do things that don't have a race but cannot be proven within the context of rust to not have a data race.
In safe Rust, yes, you must prove it. But in unsafe Rust, it's up to you. It's the exact same thing.
In safe Rust, yes, you must prove it. But in unsafe Rust, it's up to you. It's the exact same thing.