Locked bootloader are generally a development killer on many devices. Without being able to install custom kernels, development for the device becomes very tedious, and there is often no possible workaround for the remaining ROM defects.
Sony is one of the few OEMs that allows users to unlock their bootloaders. This unfortunately doesn’t mean that all users can unlock. Sometimes, carriers put restrictions in place to prevent users from flashing custom kernels. This is a wise choice for the carriers to prevent device damage through improper flashing, but a very frustrating situation for experienced users. The Sony Xperia SP has the same problem, luckily the XDA Forum Member bagyusz managed to port a few source-built custom ROMs to devices with locked bootloader. This time, bagyusz delivers an unofficial port of CyanogenMod 12, bringing the Lollipop experience to the Huashan users.
The port is still very early, so you need to keep in mind that lots of functions will not work. Currently, the unofficial CM12 has several broken items including Wi-Fi, NFC, Camera, FM Radio, and posibly more. You can’t consider it as a daily driver, but it’s a nice to see such achievements, especially when resorting to a hijacked ramdisk.