> On Mar 26, 2019, at 10:06 PM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > >> On Tue, Mar 26, 2019 at 09:29:14PM -0700, Andy Lutomirski wrote: >>> On Tue, Mar 26, 2019 at 5:31 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: >>> >>>> On Tue, Mar 26, 2019 at 12:20:24PM -0700, Andy Lutomirski wrote: >>>> On Tue, Mar 26, 2019 at 11:28 AM Matthew Garrett >>>> <matthewgarrett@xxxxxxxxxx> wrote: >>>>> >>>>> From: Matthew Garrett <mjg59@xxxxxxxxxx> >>>>> >>>>> debugfs has not been meaningfully audited in terms of ensuring that >>>>> userland cannot trample over the kernel. At Greg's request, disable >>>>> access to it entirely when the kernel is locked down. This is done at >>>>> open() time rather than init time as the kernel lockdown status may be >>>>> made stricter at runtime. >>>> >>>> Ugh. Some of those files are very useful. Could this perhaps still >>>> allow O_RDONLY if we're in INTEGRITY mode? >>> >>> Useful for what? Debugging, sure, but for "normal operation", no kernel >>> functionality should ever require debugfs. If it does, that's a bug and >>> should be fixed. >>> >> >> I semi-regularly read files in debugfs to diagnose things, and I think >> it would be good for this to work on distro kernels. > > Doing that for debugging is wonderful. People who want this type of > "lock down" are trading potential security for diagnositic ability. > I think you may be missing the point of splitting lockdown to separate integrity and confidentiality. Can you actually think of a case where *reading* a debugfs file can take over a kernel?
