I think it depends on the direction the motor was already spinning.
Say you had HS1 and LS2 on, and then you wanted to break the motor. To break, you would turn off HS2 and LS2, and turn on just LS1. This would provide a reverse current path through LS1, through the diode in LS2, and through the motor, in the opposite direction breaking it.
The other case would be having HS2 and LS1 on to start, and then to break, turning off HS2 and LS1, and turning on just LS2.
I think turning on LS1 and LS2 at the same time for breaking would also work for both starting cases, even though one of the mosfets still shouldn't actually be conducting a whole lot during that time, but this simplification may be worth it.
I have never tried this, but this link makes me thing that this may work:
https://electronics.stackexchange.com/questions/56186/how-can-i-implement-regenerative-braking-of-a-dc-motor