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=-9.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 7D020C2D0C7 for ; Wed, 11 Dec 2019 16:17:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4CC71222C4 for ; Wed, 11 Dec 2019 16:17:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="N78kdbeA" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730300AbfLKQRf (ORCPT ); Wed, 11 Dec 2019 11:17:35 -0500 Received: from mail.efficios.com ([167.114.142.138]:44020 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729973AbfLKQRY (ORCPT ); Wed, 11 Dec 2019 11:17:24 -0500 Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 4DCBC686C36; Wed, 11 Dec 2019 11:17:23 -0500 (EST) Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10032) with ESMTP id UiFR_Ndqp7KF; Wed, 11 Dec 2019 11:17:23 -0500 (EST) Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id E1BE8686C16; Wed, 11 Dec 2019 11:17:22 -0500 (EST) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com E1BE8686C16 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1576081042; bh=CW7O/eexWxWU/jqLoVA/R48UmfGB4ZgQkMjz0vziYZ4=; h=From:To:Date:Message-Id; b=N78kdbeAoUT6+6zZxmcukQlaGitp3OE6qtADiHTpYxB/0vMclZonHI4s/lV/vX+rp HLftT7/FmObmCkQ5bGMtwiHsQYr7IrXrlPvgikhxSoLOvjRpm2tBkZpgqqVChCz+wy EUC7SIvZvs9IZ307BhoQ44SwDgEVhl1XnbEGfXyUt0OEQPykGqFRyvI+mRx0GTrBUk zJyaEvvvxwSy31DEonacsfNHVJ+MHzVHkHPxbXIIE59RKoOh+nCIAERVZZB/0iWmGl XmX6My7PQpFDDzdnhBzSCinvTwoDEX7mi2h8Fw8FLxIrWWPY3Oghlb6xERwZ0x+b8a AGw1J6UKX+wLw== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10026) with ESMTP id UR1g6HRdpZL3; Wed, 11 Dec 2019 11:17:22 -0500 (EST) Received: from localhost.localdomain (192-222-181-218.qc.cable.ebox.net [192.222.181.218]) by mail.efficios.com (Postfix) with ESMTPSA id 9FE94686C04; Wed, 11 Dec 2019 11:17:22 -0500 (EST) From: Mathieu Desnoyers To: Thomas Gleixner Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , "Paul E . McKenney" , Boqun Feng , "H . Peter Anvin" , Paul Turner , linux-api@vger.kernel.org, stable@vger.kernel.org, Mathieu Desnoyers , Dmitry Vyukov , Neel Natu Subject: [PATCH for 5.5 2/3] rseq: Fix: Unregister rseq for clone CLONE_VM Date: Wed, 11 Dec 2019 11:17:12 -0500 Message-Id: <20191211161713.4490-3-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20191211161713.4490-1-mathieu.desnoyers@efficios.com> References: <20191211161713.4490-1-mathieu.desnoyers@efficios.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Cc: Thomas Gleixner Cc: Peter Zijlstra (Intel) Cc: "Paul E. McKenney" Cc: Boqun Feng Cc: "H . Peter Anvin" Cc: Paul Turner Cc: Dmitry Vyukov Cc: Neel Natu Cc: linux-api@vger.kernel.org Cc: # v4.18+ --- 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 467d26046416..716ad1d8d95e 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; -- 2.17.1