There are a whole slew of conventions that have the force of law amongst signatories.
You can read the text of the conventions as they apply under Canadian Law here:
http://laws.justice.gc.ca/en/G-3/The conventions are pretty much the same everywhere...after all that is the point of a multilateral agreement.
http://laws.justice.gc.ca/en/G-3/61388.html#rid-61397Paragraphs 1, 2 and 3 are important.
All of article 37 is important as is Article 38 and 39. Canada has knowingly violated Article 40 in the case of SS troops during the Second World War. Article 41 says you can't shoot prisoners.
Just taking a quick look through the list...it seems that one side seems pretty intent on violating just about all of it.
Iraq, The Untied States of America, England, Australia and the other comnbatants are all signatories to the Conventions on War signed in Geneva, 1949.