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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,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 CA6ABC35242 for ; Fri, 24 Jan 2020 14:38:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A1397206F0 for ; Fri, 24 Jan 2020 14:38:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579876713; bh=AmEqEAEwhWaxYqsep9Gus/Ym4kZ63m22rEoB5FCfM7k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=RC3ZgaBsYFR+pTIXK+iD+EtDO5r2/slDQvhu083RdRfHffmI8ZEdJOW2BeuiAe253 5mOEsRmbgfuiHGGMbMiC/aAqBXP+bwCYyrr9qEGlaWH/rjJ0piuKwnlvqhVJN3yFZI INqK+zYBZkJCDIzznXJeX7Bavwojt8CM1dG7lZUU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2403755AbgAXOSo (ORCPT ); Fri, 24 Jan 2020 09:18:44 -0500 Received: from mail.kernel.org ([198.145.29.99]:38316 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390973AbgAXOSk (ORCPT ); Fri, 24 Jan 2020 09:18:40 -0500 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1AE4A218AC; Fri, 24 Jan 2020 14:18:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579875519; bh=AmEqEAEwhWaxYqsep9Gus/Ym4kZ63m22rEoB5FCfM7k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=P73BQOve2iRv5lWKILfxqKIvoVsQ1YrbvVcdlF6wMcCiU+KeViENELaWRo/hVueOj GYMqrbDHgZzkXVpkBEu28Wrd6XZnoEjAe0kP2iTeZMVkcRhm9wBwEKqfSG9XychtMt vxOI/uQ4t+SmZCMGtHbmO5fT6+QJrkt4VSFFnZgo= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Mathieu Desnoyers , Peter Zijlstra , Linus Torvalds , Thomas Gleixner , Ingo Molnar , Sasha Levin Subject: [PATCH AUTOSEL 5.4 019/107] rseq: Unregister rseq for clone CLONE_VM Date: Fri, 24 Jan 2020 09:16:49 -0500 Message-Id: <20200124141817.28793-19-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200124141817.28793-1-sashal@kernel.org> References: <20200124141817.28793-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Mathieu Desnoyers [ Upstream commit 463f550fb47bede3a5d7d5177f363a6c3b45d50b ] 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 Signed-off-by: Sasha Levin --- 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 775503573ed70..b968d736833bb 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1915,11 +1915,11 @@ 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; -- 2.20.1