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Message-ID: <20171027133301.GA612@tigerII.localdomain>
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
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