linux-kernel - Re: RFC: introduce "K" flag for printf, similar to %pK

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Message-ID: <1295977273.4316.3.camel@Joe-Laptop>
Date:	Tue, 25 Jan 2011 09:41:13 -0800
From:	Joe Perches <joe@...ches.com>
To:	Kees Cook <kees.cook@...onical.com>
Cc:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Tejun Heo <tj@...nel.org>, Marcus Meissner <meissner@...e.de>,
	Jason Wessel <jason.wessel@...driver.com>,
	Eugene Teo <eugeneteo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bjorn Helgaas <bjorn.helgaas@...com>,
	Len Brown <len.brown@...el.com>,
	Changli Gao <xiaosuo@...il.com>,
	Dan Rosenberg <drosenberg@...curity.com>
Subject: Re: RFC: introduce "K" flag for printf, similar to %pK

On Tue, 2011-01-25 at 09:28 -0800, Kees Cook wrote:
> On Mon, Jan 24, 2011 at 06:17:04PM -0800, Joe Perches wrote:
> > On Mon, 2011-01-24 at 18:03 -0800, Kees Cook wrote:
> > > In the interests of hiding kernel addresses from userspace (without
> > > messing with file permissions), I want to use %pK for /proc/kallsyms and
> > > /proc/modules, but this results in changing several %x's to %p's. The
> > > primary side-effects is that some legitimately "0" value things in
> > > /proc/kallsyms turn into "(null)".
> > 
> > Another option would be to allow '0' for
> > kernel pointers.
> 
> But then this changes the behavior of %p where (null) is expected. (i.e.
> when switching from %p to %pK.)

If you really want no change to any existing cases,
change it to "%pk" and a new case label.

> I'm personally fine with that, as I suspect anything parsing the output
> that can handle finding "(null)" will be fine with "0" too. But the other
> way around, not so much. :)

Maybe there's a case where somebody changed a kernel pointer
from %p to %pK that demands "(null)", but I can't think of one.

cheers, Joe

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