From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753451AbdK2X6l (ORCPT ); Wed, 29 Nov 2017 18:58:41 -0500 Received: from out4-smtp.messagingengine.com ([66.111.4.28]:40003 "EHLO out4-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752840AbdK2X6j (ORCPT ); Wed, 29 Nov 2017 18:58:39 -0500 X-ME-Sender: Date: Thu, 30 Nov 2017 10:58:34 +1100 From: "Tobin C. Harding" To: Kaiwan N Billimoria Cc: Kees Cook , kernel-hardening@lists.openwall.com, LKML , Network Development , Steven Rostedt , Tycho Andersen Subject: Re: [kernel-hardening] Re: [RFC 0/3] kallsyms: don't leak address when printing symbol Message-ID: <20171129235834.GQ6217@eros> References: <1511821819-5496-1-git-send-email-me@tobin.cc> <20171128015041.GT17858@eros> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Mailer: Mutt 1.5.24 (2015-08-30) User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 28, 2017 at 08:58:44AM +0530, Kaiwan N Billimoria wrote: > On Tue, Nov 28, 2017 at 7:20 AM, Tobin C. Harding wrote: > > > > Noob question: how do we _know_ this. In other words how do we know no > > userland tools rely on the current behaviour? No stress to answer Kees, > > this is a pretty general kernel dev question. > > Perhaps I'm reading this wrong, but anyway: besides ftrace, kprobes > will require a > symbol-to-address lookup. Specifically, in the function > kprobe_lookup_name() which > in turn invokes kallsyms_lookup_name(). We should be right for this call chain because the patch doesn't touch kallsyms_lookup_name(). > AFAIK, SystemTap (userland) is built on top of the kprobes infrastructure.. This actually indirectly answers the concern. Since no userland tool should be looking up a kernel address the only code we can break is kernel code. thanks, Tobin