tracefs splats in lockdown=confidentiality mode

[Jordan Glover]

On Friday, November 1, 2019 10:15 PM, Steven Rostedt <rostedt at goodmis.org> wrote:

> On Fri, 1 Nov 2019 15:08:03 -0600
> dann frazier dann.frazier at canonical.com wrote:
>
> > hey,
> > fyi, I'm seeing a bunch of errors from tracefs when booting 5.4-rc5 in
> > lockdown=confidentiality mode:
> > [ 1.763630] Lockdown: swapper/0: use of tracefs is restricted; see man kernel_lockdown.7
> > [ 1.772332] Could not create tracefs 'available_events' entry
> > [ 1.778633] Lockdown: swapper/0: use of tracefs is restricted; see man kernel_lockdown.7
> > [ 1.787095] Could not create tracefs 'set_event' entry
> > [ 1.792412] Lockdown: swapper/0: use of tracefs is restricted; see man kernel_lockdown.7
> > (...)
> > [ 2.899481] Could not create tracefs 'set_graph_notrace' entry
> > [ 2.905671] Lockdown: swapper/0: use of tracefs is restricted; see man kernel_lockdown.7
> > [ 2.913934] ------------[ cut here ]------------
> > [ 2.918435] Could not register function stat for cpu 0
> > [ 2.923717] WARNING: CPU: 1 PID: 1 at kernel/trace/ftrace.c:987 ftrace_init_tracefs_toplevel+0x168/0x1bc
> > [ 2.933939] Modules linked in:
> > [ 2.937290] CPU: 1 PID: 1 Comm:
>
> Looks to me that it's working as designed ;-)
>
> I'm guessing we could quiet these warnings for boot up though. :-/
>
> But there should be at least one message that states that the tracefs
> files are not being created due to lockdown.
>
> -- Steve

Could you clarify what functionality is lost here and if it affects
system stability?

I agree that triggering WARNING on every boot with supported kernel
configuration isn't optimal experience for users.

Jordan