Jailbreak is bad, the hardware may be your property, but the software that runs on it is just licensed to you by Sony.
This is a direct transcript from the EULA:
2. RESTRICTIONS
You may not lease, rent, sublicense, publish, modify, patch, adapt or translate System Software.
If you do this, Sony has the right to sue your ass to the moon and back, since you're breaking the license agreement that you agreed with by using your PS4.