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Date: Wed, 18 Oct 2017 10:15:59 +1100
From: "Tobin C. Harding" <me@...in.cc>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: kernel-hardening@...ts.openwall.com,
Linus Torvalds <torvalds@...ux-foundation.org>,
Kees Cook <keescook@...omium.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Tycho Andersen <tycho@...ker.com>,
"Roberts, William C" <william.c.roberts@...el.com>,
Tejun Heo <tj@...nel.org>,
Jordan Glover <Golden_Miller83@...tonmail.ch>,
Greg KH <gregkh@...uxfoundation.org>,
Petr Mladek <pmladek@...e.com>, Joe Perches <joe@...ches.com>,
Ian Campbell <ijc@...lion.org.uk>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>, Chris Fries <cfries@...gle.com>,
Dave Weinstein <olorin@...gle.com>,
Daniel Micay <danielmicay@...il.com>,
Djalal Harouni <tixxdz@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] printk: hash addresses printed with %p
On Tue, Oct 17, 2017 at 09:31:19AM -0400, Steven Rostedt wrote:
> On Tue, 17 Oct 2017 15:52:51 +1100
> "Tobin C. Harding" <me@...in.cc> wrote:
>
> > Currently there are many places in the kernel where addresses are being
> > printed using an unadorned %p. Kernel pointers should be printed using
> > %pK allowing some control via the kptr_restrict sysctl. Exposing addresses
> > gives attackers sensitive information about the kernel layout in memory.
> >
> > We can reduce the attack surface by hashing all addresses printed with
> > %p. This will of course break some users, forcing code printing needed
> > addresses to be updated.
> >
> > For what it's worth, usage of unadorned %p can be broken down as follows
> >
> > git grep '%p[^KFfSsBRrbMmIiEUVKNhdDgCGO]' | wc -l
>
> Does %p[FfSs] leak addresses? Well, I guess it does if they are not
> found in kallsyms, but otherwise you have:
>
> function+0x<offset>
You are correct %pF and %pS print an offset. Does this provide an attack vector,
I didn't think so but I'm no security expert. If they do then we need to amend
those calls also.
We still have %pa[pd] to see to as well obviously.
thanks for the review,
Tobin.
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