open access - Submitting ACM Conference papers to ArXiv - Academia Stack Exchange

" ... SHERPA/Romeo shows ACM as being a 'Green Publisher', which would support the case that I can upload to ArXiv. Dissem.in states that I can upload pre- or postprints under certain circumstances, but does not explicitly mention Arxiv, positively or negatively. So, what is it? Can I submit a paper I published with an ACM Conference (ACM WiSec, if that makes a difference) to ArXiv or not? As I understand it, ArXiv is a non-profit, so it would fit the terms of the publishing policy. Or is this related to the rights you have to grant ArXiv upon submission? If I can only publish a specific version of the paper, which one? ..."