linux-kernel - Re: [PATCH V8 0/2] printk: hash addresses printed with %p

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Date:   Fri, 27 Oct 2017 22:33:01 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     "Tobin C. Harding" <me@...in.cc>
Cc:     kernel-hardening@...ts.openwall.com,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Theodore Ts'o <tytso@....edu>,
        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 <wilal.deacon@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        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 V8 0/2] printk: hash addresses printed with %p

On (10/26/17 13:53), Tobin C. Harding 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.
> 
> With this version we include hashing of malformed specifiers also.
> Malformed specifiers include incomplete (e.g %pi) and also non-existent
> specifiers. checkpatch should warn for non-existent specifiers but
> AFAICT won't warn for incomplete specifiers.
> 
> Here is the behaviour that this set implements.
> 
> For kpt_restrict==0
> 
> Randomness not ready:
>   printed with %p: 		(pointer)          # NOTE: with padding
> Valid pointer:
>   printed with %pK: 		deadbeefdeadbeef
>   printed with %p: 		0xdeadbeef
>   malformed specifier (eg %i):  0xdeadbeef
> NULL pointer:
>   printed with %pK: 		0000000000000000
>   printed with %p: 		(null)               # NOTE: no padding
>   malformed specifier (eg %i):  (null)

a quick question:
 do we care about cases when kernel pointers are printed with %x/%X and
 not with %p?

	-ss