linux-kernel - Re: [PATCH v2] printk: hash addresses printed with %p

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Date:   Tue, 17 Oct 2017 09:31:19 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Tobin C. Harding" <me@...in.cc>
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, 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>

-- Steve


> 
> arch: 2512
> block: 20
> crypto: 12
> fs: 1221
> include: 147
> kernel: 109
> lib: 77
> mm: 120
> net: 1516
> security: 11
> sound: 168
> virt: 2
> drivers: 8420
> 
> Add helper function siphash_1ulong(). Add function ptr_to_id() to map an
> address to a 32 bit unique identifier.
> 
> Signed-off-by: Tobin C. Harding <me@...in.cc>
> ---
>