[kmeisthax]

IMO proprietary modules have never been kosher. They rely on a particular legal interpretation of the GPL that assumes that...

1. "Programs" (as defined by the GPL) can be legally separate works and share the same address space (on a platform where this arrangement is highly unusual)

2. Separate GPL Programs hosted in the same address space can share linked symbols determined to not be "internal APIs" (in a world where the Supreme Court might run roughshod over this and just say all API implementation is copyright-infringing)

3. "Operating system kernel" and "GPU driver for that self-same kernel" can be considered, regardless of address space colocation, to be separate GPL Programs.

This interpretation is highly unusual but holds primarily because Linus Torvalds and every other major kernel contributor endorsed it. Whether or not this constitutes promissory estoppel, implied license, or something else is up to Nvidia legal to decide; but it's highly likely that nobody with standing to challenge what would otherwise be an obvious GPL license violation is actually in a position to do so. Hence, Nvidia has access to a market they shouldn't.