linux-kernel - Re: [PATCH] clk: Emit a stern warning with writable debugfs enabled

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Message-Id: <20211210231209.4E7EDC00446@smtp.kernel.org>
Date:   Fri, 10 Dec 2021 15:12:07 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>
Subject: Re: [PATCH] clk: Emit a stern warning with writable debugfs enabled

Quoting Geert Uytterhoeven (2021-12-09 23:57:25)
> Hi Stephen,
> 
> On Fri, Dec 10, 2021 at 2:42 AM Stephen Boyd <sboyd@...nel.org> wrote:
> > We don't want vendors to be enabling this part of the clk code and
> > shipping it to customers. Exposing the ability to change clk frequencies
> > and parents via debugfs is potentially damaging to the system if folks
> > don't know what they're doing. Emit a strong warning so that the message
> > is clear: don't enable this outside of development systems.
> >
> > Fixes: 37215da5553e ("clk: Add support for setting clk_rate via debugfs")
> > Cc: Geert Uytterhoeven <geert+renesas@...der.be>
> > Signed-off-by: Stephen Boyd <sboyd@...nel.org>
> 
> Thanks for your patch!
> 
> > --- a/drivers/clk/clk.c
> > +++ b/drivers/clk/clk.c
> > @@ -3383,6 +3383,24 @@ static int __init clk_debug_init(void)
> >  {
> >         struct clk_core *core;
> >
> > +#ifdef CLOCK_ALLOW_WRITE_DEBUGFS
> > +       pr_warn("\n");
> > +       pr_warn("********************************************************************\n");
> > +       pr_warn("**     NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE           **\n");
> > +       pr_warn("**                                                                **\n");
> > +       pr_warn("**  WRITEABLE clk DebugFS SUPPORT HAS BEEN ENABLED IN THIS KERNEL **\n");
> > +       pr_warn("**                                                                **\n");
> > +       pr_warn("** This means that this kernel is built to expose clk operations  **\n");
> > +       pr_warn("** such as parent or rate setting, enabling, disabling, etc.      **\n");
> > +       pr_warn("** to userspace, which may compromise security on your system.    **\n");
> > +       pr_warn("**                                                                **\n");
> > +       pr_warn("** If you see this message and you are not debugging the          **\n");
> > +       pr_warn("** kernel, report this immediately to your vendor!                **\n");
> > +       pr_warn("**                                                                **\n");
> > +       pr_warn("**     NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE           **\n");
> > +       pr_warn("********************************************************************\n");
> 
> So how many variants of such blocks do we have now in the kernel?
> 

Quite a few!