If anyone is getting any errors along the lines of the following:

Original Exception: OpenSSL::SSL::SSLError: SSL_connect returned=1 errno=0 state=SSLv3 read server certificate B: certificate verify failed

for any reason at all (carrierwave/fog, knife, etc.) after upgrading to Ruby 2.2.3 with rvm, reinstalling it from source fixes it:

$ rvm remove 2.2.3
$ rvm install 2.2.3 --disable-binary

Another one of those supremely obscure bugs. I hope this saves a few hours/days of desperate googling/stackoverflowing.