On 03/13/2014 10:30 PM, john.hubbard@xxxxxxxxx wrote:
From: John Hubbard <jhubbard@xxxxxxxxxx> Hi Sasha and linux-mm, Prior to commit 309381feaee564281c3d9e90fbca8963bb7428ad, it was possible to build MIT-licensed (non-GPL) drivers on Fedora. Fedora is semi-unique, in that it sets CONFIG_VM_DEBUG. Because Fedora sets CONFIG_VM_DEBUG, they end up pulling in dump_page(), via VM_BUG_ON_PAGE, via get_page(). As one of the authors of NVIDIA's new, open source, "UVM-Lite" kernel module, I originally choose to use the kernel's get_page() routine from within nvidia_uvm_page_cache.c, because get_page() has always seemed to be very clearly intended for use by non-GPL, driver code. So I'm hoping that making get_page() widely accessible again will not be too controversial. We did check with Fedora first, and they responded (https://bugzilla.redhat.com/show_bug.cgi?id=1074710#c3) that we should try to get upstream changed, before asking Fedora to change. Their reasoning seems beneficial to Linux: leaving CONFIG_DEBUG_VM set allows Fedora to help catch mm bugs.
Thanks for pointing it out. I've definitely overlooked it as a consequence of the patch. My reasoning behind making it _GPL() was simply that it's a new export, so it's GPL unless there's a really good excuse to make it non-GPL. However, dump_page() as well as the regular VM_BUG_ON() are debug functions that access functionality which isn't essential for non-GPL modules. This isn't the first and only case where enabling debug options will turn code that was previously usable under a non-GPL license into GPL specific. For example: - CONFIG_LOCKDEP* will turn locks GPL-only. - CONFIG_DYNAMIC_DEBUG will turn module loading GPL-only. - CONFIG_SUNRPC_DEBUG will turn the net RPC code GPL-only. To keep it short, my opinion is that since it doesn't break any existing code it should be kept as _GPL(), same way it was done for various other subsystems. Also, I think that enabling CONFIG_DEBUG_VM for end-users is a very risky thing to do. I agree you'll find more bugs, but you'll also hit one of the many false-positives hidden there as well. I've reported a few of those but in some cases it's hard to determine whether it's an actual false-positive or a bug somewhere else. Since the assumption is that end-users won't have CONFIG_DEBUG_VM, they don't get all the attention they deserve and end up slipping into releases: http://www.spinics.net/lists/linux-mm/msg70368.html . Actually, I can think of a few cases where having CONFIG_DEBUG_VM enabled would qualify a rather simple code to a CVE status. Thanks, Sasha -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>