linux-kernel - Re: [PATCH v2] kptr_restrict for hiding kernel pointers from unprivileged users

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Message-Id: <20101217172231.8842f5cc.akpm@linux-foundation.org>
Date:	Fri, 17 Dec 2010 17:22:31 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Dan Rosenberg <drosenberg@...curity.com>
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, netdev@...r.kernel.org,
	jmorris@...ei.org, eugeneteo@...nel.org, kees.cook@...onical.com,
	mingo@...e.hu, davem@...emloft.net
Subject: Re: [PATCH v2] kptr_restrict for hiding kernel pointers from
 unprivileged users

On Fri, 17 Dec 2010 20:12:39 -0500
Dan Rosenberg <drosenberg@...curity.com> wrote:

> > 
> > So what's next?  We need to convert 1,000,000 %p callsites to use %pK? 
> > That'll be fun.  Please consider adding a new checkpatch rule which
> > detects %p and asks people whether they should have used %pK.
> 
> The goal of this format specifier is specifically for pointers that are
> exposed to unprivileged users.  I agree that hiding all kernel pointers
> would be nice, but I don't expect the angry masses to ever agree to
> that.  For now, I'll isolate specific cases, especially in /proc, that
> are clear risks in terms of information leakage.  I'll also be skipping
> over pointers written to the syslog, since I think hiding that
> information is dmesg_restrict's job.

Well...  some administrators may wish to hide the pointer values even
for privileged callers.  That's a pretty trivial add-on for the code
which you have, and means that those admins can also suppress the
pointers for IRQ-time callers.  More /proc knobs :)

Then again, perhaps those admins would be OK if we simply disabled
plain old %p everywhere.  In which case we're looking at a separate
patch, I suggest.  

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