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=-2.2 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 EC495C2BB85 for ; Thu, 16 Apr 2020 09:45:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CAD68208E4 for ; Thu, 16 Apr 2020 09:45:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2504143AbgDPJpP (ORCPT ); Thu, 16 Apr 2020 05:45:15 -0400 Received: from mx2.suse.de ([195.135.220.15]:41080 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2503578AbgDPJpI (ORCPT ); Thu, 16 Apr 2020 05:45:08 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 08D91AE19; Thu, 16 Apr 2020 09:45:06 +0000 (UTC) Date: Thu, 16 Apr 2020 11:45:05 +0200 (CEST) From: Miroslav Benes To: Josh Poimboeuf cc: Peter Zijlstra , live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, Jessica Yu Subject: Re: [PATCH 0/7] livepatch,module: Remove .klp.arch and module_disable_ro() In-Reply-To: <20200414190814.glra2gceqgy34iyx@treble> Message-ID: References: <20200414182726.GF2483@worktop.programming.kicks-ass.net> <20200414190814.glra2gceqgy34iyx@treble> 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 On Tue, 14 Apr 2020, Josh Poimboeuf wrote: > On Tue, Apr 14, 2020 at 08:27:26PM +0200, Peter Zijlstra wrote: > > On Tue, Apr 14, 2020 at 11:28:36AM -0500, Josh Poimboeuf wrote: > > > Better late than never, these patches add simplifications and > > > improvements for some issues Peter found six months ago, as part of his > > > non-writable text code (W^X) cleanups. > > > > Excellent stuff, thanks!! > > > > I'll go brush up these two patches then: > > > > https://lkml.kernel.org/r/20191018074634.801435443@infradead.org > > https://lkml.kernel.org/r/20191018074634.858645375@infradead.org > > Ah right, I meant to bring that up. I actually played around with those > patches. While it would be nice to figure out a way to converge the > ftrace module init, I didn't really like the first patch. > > It bothers me that both the notifiers and the module init() both see the > same MODULE_STATE_COMING state, but only in the former case is the text > writable. > > I think it's cognitively simpler if MODULE_STATE_COMING always means the > same thing, like the comments imply, "fully formed" and thus > not-writable: > > enum module_state { > MODULE_STATE_LIVE, /* Normal state. */ > MODULE_STATE_COMING, /* Full formed, running module_init. */ > MODULE_STATE_GOING, /* Going away. */ > MODULE_STATE_UNFORMED, /* Still setting it up. */ > }; > > And, it keeps tighter constraints on what a notifier can do, which is a > good thing if we can get away with it. Agreed. On the other hand, the first patch would remove the tiny race window when a module state is still UNFORMED, but the protections are (being) set up. Patches 4/7 and 5/7 allow to use memcpy in that case, because it is early. But it is in fact not already. I haven't checked yet if it really matters somewhere (a race with livepatch running klp_module_coming while another module is being loaded or anything like that). Miroslav