I'm pretty sure the issue with Spectre/Meltdown is about an OS process reading other processes' (or kernel) memory. These are fundamentally chip issues, not developer issues.
See https://googleprojectzero.blogspot.com/2020/02/escaping-chro....
See https://googleprojectzero.blogspot.com/2020/02/escaping-chro....
The issue with Spectre is about an OS process (or kernel) reading its own memory - this is why in contrast to Meltdown it can't be fully fixed by CPU microcode or firmware updates, it requires mitigation in any code that enforces security boundaries, such as kernels or sandboxing VMs.