The problem is that you can't stop a solid fuel engine as it has the oxidizer mixed in it, unless it requires some sort of a catalyst that you can control.
Hybrid engines which use solid fuel and a liquid/gaseous oxidizer can be controlled better but these are often very hard to reignite.
So this means you'll have to have additional engines that are used just for the slam landing, technically possible but again might be harder to construct than a liquid engine since solid fuel engine ignition is also fairly inconsistent.
The Soyuz capsule uses rockets to soften the landing but these technically aren't propulsive landing and the landing forces tend to vary quite a bit between landings.
Overall when I think about this problem as a hobby the software isn't going to be the biggest blocker here especially considering the speeds/altitudes that we are talking about as well as the overall mass of the rocket, in fact since these rockets are going to be considerably smaller and would travel considerably slower you could absorb much more of their relative energy via hydraulics so the amount of precision needed for the slam/hover landing isn't as great.