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Date:   Thu, 28 Nov 2019 10:35:29 -0700
From:   dann frazier <dann.frazier@canonical.com>
To:     Jordan Glover <Golden_Miller83@protonmail.ch>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-security-module@vger.kernel.org" 
        <linux-security-module@vger.kernel.org>,
        Seth Forshee <seth.forshee@canonical.com>,
        Matthew Garrett <matthewgarrett@google.com>,
        James Morris <jmorris@namei.org>,
        Linux API <linux-api@vger.kernel.org>,
        Ben Hutchings <ben@decadent.org.uk>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: tracefs splats in lockdown=confidentiality mode
Message-ID: <20191128173529.GA1082355@xps13.dannf>
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On Thu, Nov 28, 2019 at 03:31:31PM +0000, Jordan Glover wrote:
> On Friday, November 1, 2019 10:15 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> > On Fri, 1 Nov 2019 15:08:03 -0600
> > dann frazier dann.frazier@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?

None that I'm aware of.

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

Yes, that's my concern.

 -dann