From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752091AbdJZCyL (ORCPT ); Wed, 25 Oct 2017 22:54:11 -0400 Received: from out4-smtp.messagingengine.com ([66.111.4.28]:48947 "EHLO out4-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751943AbdJZCyK (ORCPT ); Wed, 25 Oct 2017 22:54:10 -0400 X-ME-Sender: From: "Tobin C. Harding" To: kernel-hardening@lists.openwall.com Cc: "Tobin C. Harding" , "Jason A. Donenfeld" , "Theodore Ts'o" , Linus Torvalds , Kees Cook , Paolo Bonzini , Tycho Andersen , "Roberts, William C" , Tejun Heo , Jordan Glover , Greg KH , Petr Mladek , Joe Perches , Ian Campbell , Sergey Senozhatsky , Catalin Marinas , Will Deacon , Steven Rostedt , Chris Fries , Dave Weinstein , Daniel Micay , Djalal Harouni , linux-kernel@vger.kernel.org Subject: [PATCH V8 0/2] printk: hash addresses printed with %p Date: Thu, 26 Oct 2017 13:53:54 +1100 Message-Id: <1508986436-31966-1-git-send-email-me@tobin.cc> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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) For kpt_restrict==2 Valid pointer: printed with %pK: 0000000000000000 All other output as for kptr_restrict==0 V8: - Add second patch cleaning up null pointer printing in pointer() - Move %pK handling to separate function, further cleaning up pointer() - Move ptr_to_id() call outside of switch statement making hashing the default behaviour (including malformed specifiers). - Remove use of static_key, replace with simple boolean. V7: - Use tabs instead of spaces (ouch!). V6: - Use __early_initcall() to fill the SipHash key. - Use static keys to guard hashing before the key is available. V5: - Remove spin lock. - Add Jason A. Donenfeld to CC list by request. - Add Theodore Ts'o to CC list due to comment on previous version. V4: - Remove changes to siphash.{ch} - Do word size check, and return value cast, directly in ptr_to_id(). - Use add_ready_random_callback() to guard call to get_random_bytes() V3: - Use atomic_xchg() to guard setting [random] key. - Remove erroneous white space change. V2: - Use SipHash to do the hashing. The discussion related to this patch has been fragmented. There are three threads associated with this patch. Email threads by subject: [PATCH] printk: hash addresses printed with %p [PATCH 0/3] add %pX specifier [kernel-hardening] [RFC V2 0/6] add more kernel pointer filter options Tobin C. Harding (2): printk: remove tabular output for NULL pointer printk: hash addresses printed with %p lib/vsprintf.c | 166 +++++++++++++++++++++++++++++++++++++-------------------- 1 file changed, 108 insertions(+), 58 deletions(-) -- 2.7.4