How to turn on high-side MOSFET of a buck converter
If you are using an N channel device as shown in your diagram then yes, to fully turn on the device you need to have a gate voltage that is several volts higher than your incoming  supply voltage. However, if you used a P channel device with source connected to incoming supply, the gate being pulled down to 0 volts will turn the P channel MOSFET on. Clearly your input supply voltage needs to have a minimum value to ensure the source-gate voltage for the P channel device is sufficient for decent MOSFET activation.