From patchwork Mon Apr 5 08:53:57 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 415838 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=-18.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham 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 1E27DC433B4 for ; Mon, 5 Apr 2021 08:57:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EC02B61394 for ; Mon, 5 Apr 2021 08:57:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232952AbhDEI5G (ORCPT ); Mon, 5 Apr 2021 04:57:06 -0400 Received: from mail.kernel.org ([198.145.29.99]:36246 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232840AbhDEI5G (ORCPT ); Mon, 5 Apr 2021 04:57:06 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id A0228610E8; Mon, 5 Apr 2021 08:56:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1617613020; bh=lrID+42SZ9lI6g9WHxs5WnSEGWArFPOzvZw7wCm85bQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=CSeo8GSLXswfUym2tBHg3+IsUq+qqiTBrWQI4HXFPOcmRbvQwJS2CmHk3T5RUDk46 fL26GBYLHscSOSZrTNo8e8SszqAHwGBGYumeMuv35xAt7hEscAnoGgAcmVXZc3KqH2 t4cgHo6QOc9pKHjDOlkPTnqCtpFYNCU/hOh57K10= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Ilya Lipnitskiy , Hugh Dickins , "Eric W. Biederman" , =?utf-8?b?5ZGo55Cw5p2w?= =?utf-8?q?__?= , Linus Torvalds Subject: [PATCH 4.9 22/35] mm: fix race by making init_zero_pfn() early_initcall Date: Mon, 5 Apr 2021 10:53:57 +0200 Message-Id: <20210405085019.580637824@linuxfoundation.org> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210405085018.871387942@linuxfoundation.org> References: <20210405085018.871387942@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Ilya Lipnitskiy commit e720e7d0e983bf05de80b231bccc39f1487f0f16 upstream. There are code paths that rely on zero_pfn to be fully initialized before core_initcall. For example, wq_sysfs_init() is a core_initcall function that eventually results in a call to kernel_execve, which causes a page fault with a subsequent mmput. If zero_pfn is not initialized by then it may not get cleaned up properly and result in an error: BUG: Bad rss-counter state mm:(ptrval) type:MM_ANONPAGES val:1 Here is an analysis of the race as seen on a MIPS device. On this particular MT7621 device (Ubiquiti ER-X), zero_pfn is PFN 0 until initialized, at which point it becomes PFN 5120: 1. wq_sysfs_init calls into kobject_uevent_env at core_initcall: kobject_uevent_env+0x7e4/0x7ec kset_register+0x68/0x88 bus_register+0xdc/0x34c subsys_virtual_register+0x34/0x78 wq_sysfs_init+0x1c/0x4c do_one_initcall+0x50/0x1a8 kernel_init_freeable+0x230/0x2c8 kernel_init+0x10/0x100 ret_from_kernel_thread+0x14/0x1c 2. kobject_uevent_env() calls call_usermodehelper_exec() which executes kernel_execve asynchronously. 3. Memory allocations in kernel_execve cause a page fault, bumping the MM reference counter: add_mm_counter_fast+0xb4/0xc0 handle_mm_fault+0x6e4/0xea0 __get_user_pages.part.78+0x190/0x37c __get_user_pages_remote+0x128/0x360 get_arg_page+0x34/0xa0 copy_string_kernel+0x194/0x2a4 kernel_execve+0x11c/0x298 call_usermodehelper_exec_async+0x114/0x194 4. In case zero_pfn has not been initialized yet, zap_pte_range does not decrement the MM_ANONPAGES RSS counter and the BUG message is triggered shortly afterwards when __mmdrop checks the ref counters: __mmdrop+0x98/0x1d0 free_bprm+0x44/0x118 kernel_execve+0x160/0x1d8 call_usermodehelper_exec_async+0x114/0x194 ret_from_kernel_thread+0x14/0x1c To avoid races such as described above, initialize init_zero_pfn at early_initcall level. Depending on the architecture, ZERO_PAGE is either constant or gets initialized even earlier, at paging_init, so there is no issue with initializing zero_pfn earlier. Link: https://lkml.kernel.org/r/CALCv0x2YqOXEAy2Q=hafjhHCtTHVodChv1qpM=niAXOpqEbt7w@mail.gmail.com Signed-off-by: Ilya Lipnitskiy Cc: Hugh Dickins Cc: "Eric W. Biederman" Cc: stable@vger.kernel.org Tested-by: 周琰杰 (Zhou Yanjie) Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/memory.c +++ b/mm/memory.c @@ -132,7 +132,7 @@ static int __init init_zero_pfn(void) zero_pfn = page_to_pfn(ZERO_PAGE(0)); return 0; } -core_initcall(init_zero_pfn); +early_initcall(init_zero_pfn); #if defined(SPLIT_RSS_COUNTING)