Assuming the M1 GPU works like most modern GPUs then bounds checking is already built into every memory operation.

Memory operations in modern GPUs basically evolved from fetching textures (which intrinsically have bounds checking built in, they have a width and height). All modern desktop GPUs (and probably mobile GPUs these days) use "descriptors" for textures and buffers which specify both address and size. Out of range fetches from a buffer return 0 and out of range writes are no operations.

There have been some GPUs in the past that could literally write to any address in main memory (famously the GPU in the XBox360 could do this), but its not true of any modern GPU as far as I know.

On a different note, 900 GFlops from a GPU is not really that impressive. Desktop GPUs reached this kind of performance nearly 10 years ago, but I guess its not bad for a first generation new design.