modules: only allow symbol_get of EXPORT_SYMBOL_GPL modules

commit 9011e49d54dcc7653ebb8a1e05b5badb5ecfa9f9 upstream.

It has recently come to my attention that nvidia is circumventing the
protection added in 262e6ae7081d ("modules: inherit
TAINT_PROPRIETARY_MODULE") by importing exports from their proprietary
modules into an allegedly GPL licensed module and then rexporting them.

Given that symbol_get was only ever intended for tightly cooperating
modules using very internal symbols it is logical to restrict it to
being used on EXPORT_SYMBOL_GPL and prevent nvidia from costly DMCA
Circumvention of Access Controls law suites.

All symbols except for four used through symbol_get were already exported
as EXPORT_SYMBOL_GPL, and the remaining four ones were switched over in
the preparation patches.

Fixes: 262e6ae7081d ("modules: inherit TAINT_PROPRIETARY_MODULE")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>