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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 16322C433E0 for ; Mon, 11 Jan 2021 21:46:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DD11122CAF for ; Mon, 11 Jan 2021 21:46:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387560AbhAKVqF (ORCPT ); Mon, 11 Jan 2021 16:46:05 -0500 Received: from mga14.intel.com ([192.55.52.115]:20892 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731682AbhAKVqE (ORCPT ); Mon, 11 Jan 2021 16:46:04 -0500 IronPort-SDR: PIdsy3Zxk0jwQ23aW2KsWnxbcjjzxyJYh1AoDJ1fORsXh+oDsGWa+APuLor2nUytnjlNDzzgvd e/AUCF+2cWNw== X-IronPort-AV: E=McAfee;i="6000,8403,9861"; a="177166209" X-IronPort-AV: E=Sophos;i="5.79,339,1602572400"; d="scan'208";a="177166209" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Jan 2021 13:45:08 -0800 IronPort-SDR: /EYgtN6RyiajNarZm1QuziXZRJmrrwZcrPFB6ZrKQDG+4v0wQOeZWxJaoRULpM/ZF8lHay2iho V+jp2RHT8YtA== X-IronPort-AV: E=Sophos;i="5.79,339,1602572400"; d="scan'208";a="352760865" Received: from agluck-desk2.sc.intel.com ([10.3.52.68]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Jan 2021 13:45:08 -0800 From: Tony Luck To: Borislav Petkov Cc: Tony Luck , x86@kernel.org, Andrew Morton , Peter Zijlstra , Darren Hart , Andy Lutomirski , linux-kernel@vger.kernel.org, linux-edac@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery Date: Mon, 11 Jan 2021 13:44:50 -0800 Message-Id: <20210111214452.1826-2-tony.luck@intel.com> X-Mailer: git-send-email 2.21.1 In-Reply-To: <20210111214452.1826-1-tony.luck@intel.com> References: <20210108222251.14391-1-tony.luck@intel.com> <20210111214452.1826-1-tony.luck@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Recovery action when get_user() triggers a machine check uses the fixup path to make get_user() return -EFAULT. Also queue_task_work() sets up so that kill_me_maybe() will be called on return to user mode to send a SIGBUS to the current process. But there are places in the kernel where the code assumes that this EFAULT return was simply because of a page fault. The code takes some action to fix that, and then retries the access. This results in a second machine check. While processing this second machine check queue_task_work() is called again. But since this uses the same callback_head structure that was used in the first call, the net result is an entry on the current->task_works list that points to itself. When task_work_run() is called it loops forever in this code: do { next = work->next; work->func(work); work = next; cond_resched(); } while (work); Add a "mce_busy" flag bit to detect this situation and panic when it happens. Signed-off-by: Tony Luck --- arch/x86/kernel/cpu/mce/core.c | 7 ++++++- include/linux/sched.h | 3 ++- 2 files changed, 8 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c index 13d3f1cbda17..1bf11213e093 100644 --- a/arch/x86/kernel/cpu/mce/core.c +++ b/arch/x86/kernel/cpu/mce/core.c @@ -1246,6 +1246,7 @@ static void kill_me_maybe(struct callback_head *cb) struct task_struct *p = container_of(cb, struct task_struct, mce_kill_me); int flags = MF_ACTION_REQUIRED; + p->mce_busy = 0; pr_err("Uncorrected hardware memory error in user-access at %llx", p->mce_addr); if (!p->mce_ripv) @@ -1268,6 +1269,7 @@ static void kill_me_maybe(struct callback_head *cb) static void queue_task_work(struct mce *m, int kill_current_task) { + current->mce_busy = 1; current->mce_addr = m->addr; current->mce_kflags = m->kflags; current->mce_ripv = !!(m->mcgstatus & MCG_STATUS_RIPV); @@ -1431,8 +1433,11 @@ noinstr void do_machine_check(struct pt_regs *regs) mce_panic("Failed kernel mode recovery", &m, msg); } - if (m.kflags & MCE_IN_KERNEL_COPYIN) + if (m.kflags & MCE_IN_KERNEL_COPYIN) { + if (current->mce_busy) + mce_panic("Multiple copyin", &m, msg); queue_task_work(&m, kill_current_task); + } } out: mce_wrmsrl(MSR_IA32_MCG_STATUS, 0); diff --git a/include/linux/sched.h b/include/linux/sched.h index 6e3a5eeec509..a763a76eac57 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1360,7 +1360,8 @@ struct task_struct { u64 mce_addr; __u64 mce_ripv : 1, mce_whole_page : 1, - __mce_reserved : 62; + mce_busy : 1, + __mce_reserved : 61; struct callback_head mce_kill_me; #endif -- 2.21.1