linux-kernel - Re: [RFC PATCH] cmdline: Hide "debug" from /proc/cmdline

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Message-ID: <20140402221212.GD16570@mguzik.redhat.com>
Date:	Thu, 3 Apr 2014 00:12:13 +0200
From:	Mateusz Guzik <mguzik@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
	Ingo Molnar <mingo@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Kay Sievers <kay@...y.org>
Subject: Re: [RFC PATCH] cmdline: Hide "debug" from /proc/cmdline

On Wed, Apr 02, 2014 at 02:42:19PM -0400, Steven Rostedt wrote:
> It has come to our attention that a system running a specific user
> space init program will not boot if you add "debug" to the kernel
> command line. What happens is that the user space tool parses the
> kernel command line, and if it sees "debug" it will spit out so much
> information that the system fails to boot. This basically renders the
> "debug" option for the kernel useless.
> 
> This bug has been reported to the developers of said tool
> here:
> 
>   https://bugs.freedesktop.org/show_bug.cgi?id=76935
> 
> The response is:
> 
> "Generic terms are generic, not the first user owns them."
> 
> That is, the "debug" statement on the *kernel* command line is not
> owned by the kernel just because it was the first user of it, and
> they refuse to fix their bug.
> 
> Well, my response is, we OWN the kernel command line, and as such, we
> can keep the users from seeing stuff on it if we so choose. And with
> that, I propose this patch, which hides "debug" from /proc/cmdline,
> such that we don't have to worry about tools parsing for it and causing
> hardship for those trying to debug the kernel.
> 

Well, parsing kernel cmdline by systemd is a bad idea, and hiding
"debug" is even worse. What will happen when the next keyword clashes?
And how should I check the kernel is booted with "debug"?

If there is a real need to pass arguments to systemd, how about a
dedicated option (initargs= or whatever, where it has to be last in
cmdline), then systemd would be spawned with these arguments and would
just go over its argv.

-- 
Mateusz Guzik
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