linux-kernel - Re: [PATCH v2][GIT PULL] tracing: Prevent unloadable modules from using trace

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Date:	Fri, 22 Oct 2010 14:13:28 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2][GIT PULL] tracing: Prevent unloadable modules from using trace_bprintk()

On Fri, 22 Oct 2010 09:04:23 am Steven Rostedt wrote:
> On Fri, 2010-10-22 at 08:05 +1030, Rusty Russell wrote:
> > On Fri, 22 Oct 2010 12:15:42 am Steven Rostedt wrote:
> > > 
> > > Ingo,
> > > 
> > > This is based off of my core-2 branch. I'm moved this patch after that
> > > so if anyone has any objections, I can change this patch without holding
> > > off the previous one.
> > 
> > I think disabling use in modules is lazy,
> 
> and safer.

Well then just delete trace_bprintk altogether.  Even safer!

> > Can't you detect this on module unload and fix it up?  Or delay freeing the
> > module until the trace ring is emptied?
> 
> One possibility is to magically make all string formats used in
> trace_printk into its own section, and keep it allocated until the ring
> buffer is empty. Or, we can just do that with the module's entire string
> section, since we know whether or not that module has a trace_printk in
> it or not.

Exactly.  Set a flag in the module if it resolves trace_printk, and defer freeing
the module in that case.  This shouldn't be that hard...

Rusty.
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