With the machine code in memory, cast its address to a function pointer. Of course you need to comply with the C calling convention.
On most desktop OSes, you'll need to change memory permissions to mark it executable, e.g. on Windows call VirtualProtect and on Linux mprotect.
Binary machine instructions are not cross-platform. You will need to generate different code for each processor architecture.
No driver is needed as long as the code only requires user-level permissions.
