From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_2 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B6166C433DF for ; Fri, 24 Jul 2020 16:35:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 88EF0206C1 for ; Fri, 24 Jul 2020 16:35:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726878AbgGXQfb (ORCPT ); Fri, 24 Jul 2020 12:35:31 -0400 Received: from mail.kernel.org ([198.145.29.99]:54466 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726719AbgGXQfb (ORCPT ); Fri, 24 Jul 2020 12:35:31 -0400 Received: from oasis.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 2CCFA20674; Fri, 24 Jul 2020 16:35:30 +0000 (UTC) Date: Fri, 24 Jul 2020 12:35:28 -0400 From: Steven Rostedt To: Oscar Carter Cc: Ingo Molnar , Kees Cook , linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com, Jann Horn Subject: Re: [PATCH v2 2/2] kernel/trace: Remove function callback casts Message-ID: <20200724123528.36ea9c9e@oasis.local.home> In-Reply-To: <20200724161921.GA3123@ubuntu> References: <20200719155033.24201-1-oscar.carter@gmx.com> <20200719155033.24201-3-oscar.carter@gmx.com> <20200721140545.445f0258@oasis.local.home> <20200724161921.GA3123@ubuntu> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 24 Jul 2020 18:19:21 +0200 Oscar Carter wrote: > > The linker trick is far less intrusive, and I believe less error prone. > > If we use the linker trick, the warning -Wcast-function-type dissapears, > but in a way that makes impossible to the compiler to get the necessary > info about function prototypes to insert the commented check. As far I > know, this linker trick (redirection of a function) is hidden for the > CFI build. > > So, in my opinion, the linker trick is not suitable if we want to protect > the function pointers of the ftrace subsystem against an attack that > modifiy the normal flow of the kernel. The linker trick should only affect architectures that don't implement the needed features. I can make it so the linker trick is only applied to those archs, and other archs that want more protection only need to add these features to their architectures. It's much less intrusive than this patch. -- Steve