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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 8C828ECE588 for ; Tue, 15 Oct 2019 14:13:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6CA4E2054F for ; Tue, 15 Oct 2019 14:13:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732594AbfJOONr (ORCPT ); Tue, 15 Oct 2019 10:13:47 -0400 Received: from mx2.suse.de ([195.135.220.15]:44588 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1732500AbfJOONq (ORCPT ); Tue, 15 Oct 2019 10:13:46 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 30A43B450; Tue, 15 Oct 2019 14:13:44 +0000 (UTC) Date: Tue, 15 Oct 2019 16:13:41 +0200 (CEST) From: Miroslav Benes To: Peter Zijlstra cc: Jessica Yu , Steven Rostedt , x86@kernel.org, linux-kernel@vger.kernel.org, mhiramat@kernel.org, bristot@redhat.com, jbaron@akamai.com, torvalds@linux-foundation.org, tglx@linutronix.de, mingo@kernel.org, namit@vmware.com, hpa@zytor.com, luto@kernel.org, ard.biesheuvel@linaro.org, jpoimboe@redhat.com, live-patching@vger.kernel.org Subject: Re: [PATCH v3 5/6] x86/ftrace: Use text_poke() In-Reply-To: <20191015135634.GK2328@hirez.programming.kicks-ass.net> Message-ID: References: <20191007081945.10951536.8@infradead.org> <20191008104335.6fcd78c9@gandalf.local.home> <20191009224135.2dcf7767@oasis.local.home> <20191010092054.GR2311@hirez.programming.kicks-ass.net> <20191010091956.48fbcf42@gandalf.local.home> <20191010140513.GT2311@hirez.programming.kicks-ass.net> <20191010115449.22044b53@gandalf.local.home> <20191010172819.GS2328@hirez.programming.kicks-ass.net> <20191011125903.GN2359@hirez.programming.kicks-ass.net> <20191015130739.GA23565@linux-8ccs> <20191015135634.GK2328@hirez.programming.kicks-ass.net> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [ live-patching ML CCed ] On Tue, 15 Oct 2019, Peter Zijlstra wrote: > On Tue, Oct 15, 2019 at 03:07:40PM +0200, Jessica Yu wrote: > > > > The fact that it is executable; also the fact that you do it right after > > > we mark it ro. Flipping the memory protections back and forth is just > > > really poor everything. > > > > > > Once this ftrace thing is sorted, we'll change x86 to _refuse_ to make > > > executable (kernel) memory writable. > > > > Not sure if relevant, but just thought I'd clarify: IIRC, > > klp_module_coming() is not poking the coming module, but it calls > > module_enable_ro() on itself (the livepatch module) so it can apply > > relocations and such on the new code, which lives inside the livepatch > > module, and it needs to possibly do this numerous times over the > > lifetime of the patch module for any coming module it is responsible > > for patching (i.e., call module_enable_ro() on the patch module, not > > necessarily the coming module). So I am not be sure why > > klp_module_coming() should be moved before complete_formation(). I > > hope I'm remembering the details correctly, livepatch folks feel free > > to chime in if I'm incorrect here. > > You mean it does module_disable_ro() ? That would be broken and it needs > to be fixed. Can some livepatch person explain what it does and why? Yes, it does. klp_module_coming() calls module_disable_ro() on all patching modules which patch the coming module in order to call apply_relocate_add(). New (patching) code for a module can be relocated only when the relevant module is loaded. Miroslav