On Thu, Apr 12, 2018 at 1:23 AM, Greg KH <greg@xxxxxxxxx> wrote: > On Wed, Apr 11, 2018 at 07:54:12PM -0700, Andy Lutomirski wrote: >> On Wed, Apr 11, 2018 at 1:33 PM, Greg KH <greg@xxxxxxxxx> wrote: >> > On Wed, Apr 11, 2018 at 09:09:16PM +0100, David Howells wrote: >> >> Greg KH <greg@xxxxxxxxx> wrote: >> >> >> >> > Why not just disable debugfs entirely? This half-hearted way to sorta >> >> > lock it down is odd, it is meant to not be there at all, nothing in your >> >> > normal system should ever depend on it. >> >> > >> >> > So again just don't allow it to be mounted at all, much simpler and more >> >> > obvious as to what is going on. >> >> >> >> Yeah, I agree - and then I got complaints because it seems that it's been >> >> abused to allow drivers and userspace components to communicate. >> > >> > With in-kernel code? Please let me know and I'll go fix it up to not >> > allow that, as that is not ok. >> > >> > I do know of some bad examples of out-of-tree code abusing debugfs to do >> > crazy things (battery level monitoring?), but that's their own fault... >> > >> > debugfs is for DEBUGGING! For anything you all feel should be "secure", >> > then just disable it entirely. >> > >> >> Debugfs is very, very useful for, ahem, debugging. I really think >> this is an example of why we should split lockdown into the read and >> write varieties and allow mounting and reading debugfs when only write >> is locked down. > > Ok, but be sure that there are no "secrets" in those debugging files if > you really buy into the whole "lock down" mess... > > Really, it's easier to just disable the whole thing. > I mostly agree with your sentiment. I'm saying that, for most uses, I *don't* buy into the idea that a normal secure-boot-supporting distro should block debugfs. I sometimes like to ask people who report problems to send me the contents of such-and-such file in debugfs, and I think it should keep working. Blocking write access to debugfs is mostly sensible for a lockdown system, but blocking read only makes sense if you're worried about straight-up bugs or if you think that debugfs contains protection-worthy secrets. What I want to see is: lockdown=protect_integrity: debugfs is read-only, bpf and perf are unrestricted, iopl and ioperm are disabled, etc. lockdown=protect_integrity_and_secrecy: debugfs is gone, bpf and perf are restricted, plus all the restrictions from lockdown=protect_integrity Distros should strongly prefer lockdown=protect_integrity (or lockdown=off) by default. lockdown=protect_integrity_and_secrecy is for custom setups, embedded applications, etc. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
