RE: [PATCH] printk: introduce kptr_restrict level 3

From: Roberts, William C
Date: Thu Oct 06 2016 - 09:48:26 EST

> -----Original Message-----
> From: Christoph Hellwig [mailto:hch@xxxxxxxxxxxxx]
> Sent: Thursday, October 6, 2016 9:32 AM
> To: Roberts, William C <william.c.roberts@xxxxxxxxx>
> Cc: kernel-hardening@xxxxxxxxxxxxxxxxxx; corbet@xxxxxxx; linux-
> doc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH] printk: introduce kptr_restrict level 3
> On Wed, Oct 05, 2016 at 02:04:46PM -0400, william.c.roberts@xxxxxxxxx wrote:
> > From: William Roberts <william.c.roberts@xxxxxxxxx>
> >
> > 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.