stm32flash is an alternative to STM32 Flash loader demonstrator (FLASHER-STM32) for Linux users, there are some pitfalls, though.
No Recent Releases
Although the development is still active, latest release at the time of writing is 0.5, which does not fully compatible with some of the new chips. In my case, I would have to clone the repository and compile from source in order to have those chip supported.
CH340/CH341
According to AN2606, flashing through UART requires parity support. Linux driver for CH340/CH341 does not have it until 4.10. (Kernel version of Debian Stretch is 4.9 by default.)