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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 486A5C433F5 for ; Thu, 25 Nov 2021 14:41:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355849AbhKYOov (ORCPT ); Thu, 25 Nov 2021 09:44:51 -0500 Received: from smtp-out1.suse.de ([195.135.220.28]:33820 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350311AbhKYOmp (ORCPT ); Thu, 25 Nov 2021 09:42:45 -0500 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id B3DBD212BB; Thu, 25 Nov 2021 14:39:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1637851172; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=gxDGorvSTIRGEY6nErUaWrzq7939SEFYfdrfS8HxGJY=; b=a4ESqggC1wPB6gVNyLXGDo3uT7/k0y7n7fkEwITl0odq7Mb7UcGwiLv8ZWWgeJzSgD7KvL X3rfE+ih7yhbj3Q3Ko3XfbXAJAWZcRf8NO4IEQulZlZfdog9asS3KhXcNIScfko+DRlVsK HQxV0Zkcg+OSgEtSaQyiq0qfRe0sC30= Received: from suse.cz (unknown [10.100.216.66]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 95C35A3B89; Thu, 25 Nov 2021 14:39:32 +0000 (UTC) Date: Thu, 25 Nov 2021 15:39:29 +0100 From: Petr Mladek To: Miroslav Benes Cc: jpoimboe@redhat.com, jikos@kernel.org, joe.lawrence@redhat.com, peterz@infradead.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, shuah@kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH 3/3] selftests/livepatch: Test of the API for specifying functions to search for on a stack Message-ID: References: <20211119090327.12811-1-mbenes@suse.cz> <20211119090327.12811-4-mbenes@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211119090327.12811-4-mbenes@suse.cz> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 2021-11-19 10:03:27, Miroslav Benes wrote: > Add a test for the API which allows the user to specify functions which > are then searched for on any tasks's stack during a transition process. > > --- /dev/null > +++ b/lib/livepatch/test_klp_funcstack_mod.c > @@ -0,0 +1,72 @@ > +// SPDX-License-Identifier: GPL-2.0 > +// Copyright (C) 2021 Miroslav Benes > + > +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt > + > +#include > +#include > +#include > +#include > + > +static int sleep_length = 10000; > +module_param(sleep_length, int, 0644); > +MODULE_PARM_DESC(sleep_length, "length of sleep in seconds (default=10)"); > + > +static noinline void child_function(void) > +{ > + pr_info("%s enter\n", __func__); > + msleep(sleep_length); The hardcoded sleep is not ideal. It might be too low or non-necessary high. If I get it correctly, we are trying to achieve here the same as busymod_work_func() in test_klp_callbacks_busy.c. The approach with debugfs is an interesting trick. Though, I slightly prefer using the scheduled work. The workqueue API looks less tricky to me than sysfs/debugfs API. Also it does not block the module in the init() callback[*]. But I might be biased. Anyway, it might make sense to use the same trick in both situations. It would make it easier to maintain the test modules. [*] There is actually a race in the workqueue approach. The module init() callback should wait until the work is really scheduled and sleeping. It might be achieved by similar hand-shake like with @block_transition variable. Or completion API might be even more elegant. > + pr_info("%s exit\n", __func__); > +} > + > +static noinline void child2_function(void) > +{ > + pr_info("%s\n", __func__); > +} > + > +static noinline void parent_function(void) > +{ > + pr_info("%s enter\n", __func__); > + child_function(); > + child2_function(); This would deserve some explanation what we try to simulate here and how it is achieved. It is not easy for me even with the background that I have freshly in my mind. Also I think about more descriptive names ;-) What about something like this (using workqueue work and completion): /* * Simulate part of the caller code that is in another .elf section * and is reached via jump. It this was really the case then the stack * unwinder might not be able to detect that the process is sleeping * in the caller. */ static void simulate_jump_part(void) { pr_info("%s enter\n", __func__); /* Stay in the jump part unless told to leave. */ wait_for_completion(finish_jump); pr_info("%s exit\n", __func__); } /* * Simulate modified part of the caller code. It should never get * livepatched when the caller is sleeping in the just_part(). */ static void simulate_modified_part(void) { pr_info("%s\n", __func__); } static void test_not_on_stack_func_work(struct work_struct *work) { pr_info("%s enter\n", __func__); /* Simulation ready */ complete(work_started); simulate_jump_part(); simulate_modified_part(); pr_info("%s exit\n", __func__); } static int test_klp_no_on_stack_init(void) { pr_info("%s\n", __func__); schedule_work(&work); wait_for_completion(&work_started); return 0; } static void test_not_on_stack_exit(void) { complete(&finish_jump); flush_work(&work); pr_info("%s\n", __func__); } module_init(test_klp_not_on_stack_init); module_exit(test_klp_not_on_stack_exit); > + pr_info("%s exit\n", __func__); > +} > + Best Regards, Petr