I know that foreign nationals and foreign governments are prohibited from donating money to super PACs. They are also prohibited from even indirect, non-coordinated expenditures for or against a political candidate. (which is basically what a super PAC does).
However, foreign nationals can contribute to "Social Welfare Organizations" like the NRA which, in order to be classified as a SWO, must spend less than half it's budget on political stuff. That SWO can then donate to super PACs but don't have to disclose where the money came from.
Foreign owned companies with US based subsidiaries can donate to Super PACs as well. But the super PACs are not allowed to solicit donations from foreign nationals (see Jeb Bush's fines for soliciting money from a British tobacco company for his super pac).
I would imagine that if foreign nationals setup a corporation in the US in order to funnel money to political causes, that would be illegal. But if they are using established, legitimate businesses to launder their donations, that seems to be allowed as long as we can't prove that foreign entities are earmarking specific funds to end up in PACs and campaigns in the US.