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=-11.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 88CCCC2D0DB for ; Wed, 25 Dec 2019 10:39:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 69B132077B for ; Wed, 25 Dec 2019 10:39:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727256AbfLYKjf (ORCPT ); Wed, 25 Dec 2019 05:39:35 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:40617 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726307AbfLYKjJ (ORCPT ); Wed, 25 Dec 2019 05:39:09 -0500 Received: from [5.158.153.53] (helo=tip-bot2.lab.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1ik445-00085y-Vi; Wed, 25 Dec 2019 11:38:54 +0100 Received: from [127.0.1.1] (localhost [IPv6:::1]) by tip-bot2.lab.linutronix.de (Postfix) with ESMTP id 35AFD1C2B1E; Wed, 25 Dec 2019 11:38:53 +0100 (CET) Date: Wed, 25 Dec 2019 10:38:53 -0000 From: "tip-bot2 for Mathieu Desnoyers" Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: core/urgent] rseq: Unregister rseq for clone CLONE_VM Cc: Mathieu Desnoyers , "Peter Zijlstra (Intel)" , Linus Torvalds , Thomas Gleixner , Ingo Molnar , x86 , LKML In-Reply-To: <20191211161713.4490-3-mathieu.desnoyers@efficios.com> References: <20191211161713.4490-3-mathieu.desnoyers@efficios.com> MIME-Version: 1.0 Message-ID: <157727033304.30329.10105916023248676597.tip-bot2@tip-bot2> X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the core/urgent branch of tip: Commit-ID: 463f550fb47bede3a5d7d5177f363a6c3b45d50b Gitweb: https://git.kernel.org/tip/463f550fb47bede3a5d7d5177f363a6c3b45d50b Author: Mathieu Desnoyers AuthorDate: Wed, 11 Dec 2019 11:17:12 -05:00 Committer: Ingo Molnar CommitterDate: Wed, 25 Dec 2019 10:41:20 +01:00 rseq: Unregister rseq for clone CLONE_VM It has been reported by Google that rseq is not behaving properly with respect to clone when CLONE_VM is used without CLONE_THREAD. It keeps the prior thread's rseq TLS registered when the TLS of the thread has moved, so the kernel can corrupt the TLS of the parent. The approach of clearing the per task-struct rseq registration on clone with CLONE_THREAD flag is incomplete. It does not cover the use-case of clone with CLONE_VM set, but without CLONE_THREAD. Here is the rationale for unregistering rseq on clone with CLONE_VM flag set: 1) CLONE_THREAD requires CLONE_SIGHAND, which requires CLONE_VM to be set. Therefore, just checking for CLONE_VM covers all CLONE_THREAD uses. There is no point in checking for both CLONE_THREAD and CLONE_VM, 2) There is the possibility of an unlikely scenario where CLONE_SETTLS is used without CLONE_VM. In order to be an issue, it would require that the rseq TLS is in a shared memory area. I do not plan on adding CLONE_SETTLS to the set of clone flags which unregister RSEQ, because it would require that we also unregister RSEQ on set_thread_area(2) and arch_prctl(2) ARCH_SET_FS for completeness. So rather than doing a partial solution, it appears better to let user-space explicitly perform rseq unregistration across clone if needed in scenarios where CLONE_VM is not set. Signed-off-by: Mathieu Desnoyers Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: https://lkml.kernel.org/r/20191211161713.4490-3-mathieu.desnoyers@efficios.com Signed-off-by: Ingo Molnar --- include/linux/sched.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 467d260..716ad1d 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1929,11 +1929,11 @@ static inline void rseq_migrate(struct task_struct *t) /* * If parent process has a registered restartable sequences area, the - * child inherits. Only applies when forking a process, not a thread. + * child inherits. Unregister rseq for a clone with CLONE_VM set. */ static inline void rseq_fork(struct task_struct *t, unsigned long clone_flags) { - if (clone_flags & CLONE_THREAD) { + if (clone_flags & CLONE_VM) { t->rseq = NULL; t->rseq_sig = 0; t->rseq_event_mask = 0;