The are mixed results with regard to whether tarmac, concrete, or asphalt is harmful. Tarmac/asphalt is harder than dirt. Concrete is harder than tarmac. Though the differences are not that much. People are probably more likely to get injured because of bad running form, or other factors.
You will get more benefit from proper training, form, and shoes than worrying about the running surface.
Also for perspective. 5Ks, 10Ks, half, and full marathons are typically run on roads. These distances are substantially longer than what you are running. Some runners get injured, but most don't. They run for many, many years without any knee problems.
Anecdotally, the injuries I've sustained where not because of what the surface was made of. One was because the sidewalk was slanted so my ankles got twisted up after running on that for miles. Another (more common) was just running through pain that ended up making things worse.