The GPLv2 for example asserts that it provides a permissive patent grant under the "implied license" doctrine in patent law - https://copyleft.org/guide-next/co

The GPLv2 for example asserts that it provides a permissive patent grant under the "implied license" doctrine in patent law - https://copyleft.org/guide-next/comprehensive-gpl-guidech7.html https://copyleft.org/guide-next/comprehensive-gpl-guidech7.h... But you're right, I don't think it's been exhaustively tested in court, just like most software patent issues.