You can find a module that implements the integer multiply and divide instructions at src/main/scala/alu/entnM.scala. Currently the module does not cover all instructions defined in M-extension of riscv.
To complete the design to implement every instruction in 1 cycle, complete lines 26 to line 47 in src/main/scala/alu/entnM.scala. The instruction that needs to be completed for each line is indicated by a comment. Lines 28 and 31 has been completed.
cd cpu-test/
./verilator.sh