The only trademark restrictions are in your ad copy...can't have certain words appear in the text, because that could be potentially misleading, making your site look like the brand's official site etc.
Nobody can touch your keywords...doesn't matter what I bid on...wouldn't that be ridiculous if you were not allowed to bid on names of the products you're trying to sell?
It's important to note these are North America statements.
The EU is very different in terms of trademark laws and use of trademarks in AdWords campaigns.