linux-kernel - RE: [PATCH] printk: introduce kptr

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Message-ID: <476DC76E7D1DF2438D32BFADF679FC561CD14651@ORSMSX103.amr.corp.intel.com>
Date:   Thu, 6 Oct 2016 13:47:47 +0000
From:   "Roberts, William C" <william.c.roberts@...el.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        "corbet@....net" <corbet@....net>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] printk: introduce kptr_restrict level 3

> -----Original Message-----
> From: Christoph Hellwig [mailto:hch@...radead.org]
> Sent: Thursday, October 6, 2016 9:32 AM
> To: Roberts, William C <william.c.roberts@...el.com>
> Cc: kernel-hardening@...ts.openwall.com; corbet@....net; linux-
> doc@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH] printk: introduce kptr_restrict level 3
> 
> On Wed, Oct 05, 2016 at 02:04:46PM -0400, william.c.roberts@...el.com wrote:
> > From: William Roberts <william.c.roberts@...el.com>
> >
> > Some out-of-tree modules do not use %pK and just use %p, as it's the
> > common C paradigm for printing pointers. Because of this,
> > kptr_restrict has no affect on the output and thus, no way to contain
> > the kernel address leak.
> 
> So what?  We a) don't care about out of tree modules and b) you could just triviall
> fix them up if you care.

Out of tree modules still affect core kernel security. I would also bet money, that somewhere
In-tree someone has put a %p when they wanted a %pK. So this method is just quite error
prone. We currently have a blacklist approach versus whitelist.

> 
> No need to bloat the kernel with crap like this.

It's unconstructive comments like this that do the whole community harm. Notice how
responses from Kees Cook were aimed at finding a different solution to the problem and were
very constructive. As far as "bloating" goes, it really didn't change a whole lot, most of it was moved
lines, and adds maybe a few lines of code.