From patchwork Sat Feb 17 08:18:10 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Changbin Du X-Patchwork-Id: 13561272 Received: from szxga04-in.huawei.com (szxga04-in.huawei.com [45.249.212.190]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E12401CD17; Sat, 17 Feb 2024 08:19:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.190 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708157963; cv=none; b=IKT7/arNuQHVIdqK5hQcZc2Zb+62+U93+4X4j26mm+NVSaU2Vlj8GPZiC+GHqrXEhrG94H/eb4eiCl1h3eqgp5vyFlOh3I0ZAvx1fzYMdFTKTt8/nDDFOp74OpAEnfyj0OSE+eYAJoS/kDnlEoCWELS+938FCo/ihv1nPj0iYAQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708157963; c=relaxed/simple; bh=OEujMmKsaz34R6ihVj0EBGAxb1fHPMfIT7TYuck2xHM=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=eEjNaFvNCmEAJtgg+gZ/KREedSVvVJkfgTe3QpgQWwJx0EpYtoUOkVe9ykDByeebhiFnQKFjRcHBOXegoJI6lijU/lp9EWKiZ9P7/bJFAmgV/6Qisck5cPmMyu93GMU0dUwuIvNXDAlI9KS2drM/ojGIOQm4//eIMLgsU+Y+lrE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.190 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.163.44]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4TcM952KLBz2Bcnr; Sat, 17 Feb 2024 16:17:13 +0800 (CST) Received: from kwepemd100002.china.huawei.com (unknown [7.221.188.184]) by mail.maildlp.com (Postfix) with ESMTPS id 8BD17140485; Sat, 17 Feb 2024 16:19:18 +0800 (CST) Received: from M910t.huawei.com (10.110.54.157) by kwepemd100002.china.huawei.com (7.221.188.184) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.2.1258.28; Sat, 17 Feb 2024 16:19:17 +0800 From: Changbin Du To: Andrew Morton , Luis Chamberlain CC: , , Changbin Du , Xiaoyi Su , Eric Chanudet Subject: [PATCH v3] modules: wait do_free_init correctly Date: Sat, 17 Feb 2024 16:18:10 +0800 Message-ID: <20240217081810.4155871-1-changbin.du@huawei.com> X-Mailer: git-send-email 2.25.1 Precedence: bulk X-Mailing-List: linux-modules@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To kwepemd100002.china.huawei.com (7.221.188.184) The synchronization here is just to ensure the module init's been freed before doing W+X checking. But the commit 1a7b7d922081 ("modules: Use vmalloc special flag") moves do_free_init() into a global workqueue instead of call_rcu(). So now rcu_barrier() can not ensure that do_free_init has completed. We should wait it via flush_work(). Without this fix, we still could encounter false positive reports in W+X checking, and the rcu synchronization is unnecessary which can introduce significant delay. Eric Chanudet reports that the rcu_barrier introduces ~0.1s delay on a PREEMPT_RT kernel. [ 0.291444] Freeing unused kernel memory: 5568K [ 0.402442] Run /sbin/init as init process With this fix, the above delay can be eliminated. Fixes: 1a7b7d922081 ("modules: Use vmalloc special flag") Signed-off-by: Changbin Du Cc: Xiaoyi Su Cc: Eric Chanudet Tested-by: Eric Chanudet --- v3: - amend comment in do_init_module() and update commit msg. v2: - fix compilation issue for no CONFIG_MODULES found by 0-DAY. --- include/linux/moduleloader.h | 8 ++++++++ init/main.c | 5 +++-- kernel/module/main.c | 9 +++++++-- 3 files changed, 18 insertions(+), 4 deletions(-) diff --git a/include/linux/moduleloader.h b/include/linux/moduleloader.h index 001b2ce83832..89b1e0ed9811 100644 --- a/include/linux/moduleloader.h +++ b/include/linux/moduleloader.h @@ -115,6 +115,14 @@ int module_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs, struct module *mod); +#ifdef CONFIG_MODULES +void flush_module_init_free_work(void); +#else +static inline void flush_module_init_free_work(void) +{ +} +#endif + /* Any cleanup needed when module leaves. */ void module_arch_cleanup(struct module *mod); diff --git a/init/main.c b/init/main.c index e24b0780fdff..f0b7e21ac67f 100644 --- a/init/main.c +++ b/init/main.c @@ -99,6 +99,7 @@ #include #include #include +#include #include #include @@ -1402,11 +1403,11 @@ static void mark_readonly(void) if (rodata_enabled) { /* * load_module() results in W+X mappings, which are cleaned - * up with call_rcu(). Let's make sure that queued work is + * up with init_free_wq. Let's make sure that queued work is * flushed so that we don't hit false positives looking for * insecure pages which are W+X. */ - rcu_barrier(); + flush_module_init_free_work(); mark_rodata_ro(); rodata_test(); } else diff --git a/kernel/module/main.c b/kernel/module/main.c index 36681911c05a..b0b99348e1a8 100644 --- a/kernel/module/main.c +++ b/kernel/module/main.c @@ -2489,6 +2489,11 @@ static void do_free_init(struct work_struct *w) } } +void flush_module_init_free_work(void) +{ + flush_work(&init_free_wq); +} + #undef MODULE_PARAM_PREFIX #define MODULE_PARAM_PREFIX "module." /* Default value for module->async_probe_requested */ @@ -2593,8 +2598,8 @@ static noinline int do_init_module(struct module *mod) * Note that module_alloc() on most architectures creates W+X page * mappings which won't be cleaned up until do_free_init() runs. Any * code such as mark_rodata_ro() which depends on those mappings to - * be cleaned up needs to sync with the queued work - ie - * rcu_barrier() + * be cleaned up needs to sync with the queued work by invoking + * flush_module_init_free_work(). */ if (llist_add(&freeinit->node, &init_free_list)) schedule_work(&init_free_wq);