The theory is that you get support by using metrics: you have to put figures, preferably expressed in dollars (or euros or yens) behind security. Managers manage: they take decisions, based on observed situations and goals to reach. These goals are often expressed (at least in part) in financial terms. Therefore, managers will decide to support/fund/enforce usage of security controls (say, an antivirus) based on whether this is worth the effort: the said security measures should, overall, bring in more money than was spent on them.
Since security deals with risks, the metrics must take into account both the probability of occurrence of the feared event, and the involved costs. The cost is multiform; e.g. there are "image costs" which relate to how much the business reputation is damaged, and are notoriously hard to estimate. Then any envisioned security control (e.g. antivirus) must be also estimated, both for its own intrinsic costs (e.g. antivirus license, but also extra sysadmin time, and overhead incurred by incompatibilities between the antivirus and some existing software and/or practices), and in how much it is expected to decrease the probability of attack or the costs implied by an attack.
The master concept here is: numbers. Go quantitative. Managers want figures. If you have to make "fuzzy estimates" (i.e. wild guesses), then produce more numbers: give an estimate as a number and an estimate of the reliability of the previous estimate.
The practice is a bit different, of course. Managers are people, too. They have to decide, but they don't like it. What they would really prefer is that the Chief Information Security Officer comes with a detailed analysis which ends up with a single slide with a binary choice: do this and it will save that many dollars, or don't do it and face the consequences.
Because though managers' mandate is to decide, what they really love to do is to approve or reject. You will get support from managers if you make their life easier, and that involves making all the decision work except the final "yes" or "no" stamp.
Remember that business is everything. Any decision will be taken based on how well a proposed strategy or policy aligns with the organization ultimate goals. These goals vary, but, in many cases, they can be expressed as: "Make money. A lot of.".