Low-side current sensing
You can use a differential op-amp amplifier as follows: 







simulate this circuit &ndash; Schematic created using CircuitLab

OA1 is a RRIO amplifier. 

The 'extra' resistors allows you to use a Kelvin connection to the sense resistor and thus eliminate errors due to the traces. 

R3 should be a non-inductive type. D1 and D2 are optional (could be a dual too) to clamp any transients. 

You'll get transients from the gate drivers even without the motor- a good gate driver might source a few amperes.