From patchwork Tue Nov 3 20:34:30 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 316856 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=-12.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, 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 09690C2D0A3 for ; Tue, 3 Nov 2020 21:45:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B17572236F for ; Tue, 3 Nov 2020 21:45:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604439904; bh=f0Gbn9jbJqxfQbUcd7yt9h1zWmYOK/yFEO9uOh39WtA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Dk/U3/UuhiHCusbTroad7QlX63CpFpDI9OSircNmVz48581UTSciEwIbywaRPH2Hb k+Srk45DvnfpKvkZmaPI3AWJD/uXmlZuqJiwupMBEgTprMdIkRHe6a0wzX6Ha7RtGV ao8Q7nUNymNhd1+n/eLdUVG9Lc0VKcz+Neg/Uc+U= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732360AbgKCVpA (ORCPT ); Tue, 3 Nov 2020 16:45:00 -0500 Received: from mail.kernel.org ([198.145.29.99]:51656 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732367AbgKCUxe (ORCPT ); Tue, 3 Nov 2020 15:53:34 -0500 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 600BC223AC; Tue, 3 Nov 2020 20:53:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604436813; bh=f0Gbn9jbJqxfQbUcd7yt9h1zWmYOK/yFEO9uOh39WtA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nvIfjH3Elgn5Ma1GY7fOzVgEdJgPvOAjcVEk8DahveWSjSGeoYRVjTI2ExSx/N2uR yNQcL+nRou7J3xwwhxQJ4WuoWsQDjOfKBPA30UGQcJyw8Nh1rXiRDJ+0MesArZd16m bA369D/XabXKvN2ZbtMreMLO5hZUQZWyaYHGYBxA= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Nicholas Piggin , "Peter Zijlstra (Intel)" , Michael Ellerman , Sasha Levin Subject: [PATCH 5.4 022/214] mm: fix exec activate_mm vs TLB shootdown and lazy tlb switching race Date: Tue, 3 Nov 2020 21:34:30 +0100 Message-Id: <20201103203252.045316664@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201103203249.448706377@linuxfoundation.org> References: <20201103203249.448706377@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Nicholas Piggin [ Upstream commit d53c3dfb23c45f7d4f910c3a3ca84bf0a99c6143 ] Reading and modifying current->mm and current->active_mm and switching mm should be done with irqs off, to prevent races seeing an intermediate state. This is similar to commit 38cf307c1f20 ("mm: fix kthread_use_mm() vs TLB invalidate"). At exec-time when the new mm is activated, the old one should usually be single-threaded and no longer used, unless something else is holding an mm_users reference (which may be possible). Absent other mm_users, there is also a race with preemption and lazy tlb switching. Consider the kernel_execve case where the current thread is using a lazy tlb active mm: call_usermodehelper() kernel_execve() old_mm = current->mm; active_mm = current->active_mm; *** preempt *** --------------------> schedule() prev->active_mm = NULL; mmdrop(prev active_mm); ... <-------------------- schedule() current->mm = mm; current->active_mm = mm; if (!old_mm) mmdrop(active_mm); If we switch back to the kernel thread from a different mm, there is a double free of the old active_mm, and a missing free of the new one. Closing this race only requires interrupts to be disabled while ->mm and ->active_mm are being switched, but the TLB problem requires also holding interrupts off over activate_mm. Unfortunately not all archs can do that yet, e.g., arm defers the switch if irqs are disabled and expects finish_arch_post_lock_switch() to be called to complete the flush; um takes a blocking lock in activate_mm(). So as a first step, disable interrupts across the mm/active_mm updates to close the lazy tlb preempt race, and provide an arch option to extend that to activate_mm which allows architectures doing IPI based TLB shootdowns to close the second race. This is a bit ugly, but in the interest of fixing the bug and backporting before all architectures are converted this is a compromise. Signed-off-by: Nicholas Piggin Acked-by: Peter Zijlstra (Intel) Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200914045219.3736466-2-npiggin@gmail.com Signed-off-by: Sasha Levin --- arch/Kconfig | 7 +++++++ fs/exec.c | 17 +++++++++++++++-- 2 files changed, 22 insertions(+), 2 deletions(-) diff --git a/arch/Kconfig b/arch/Kconfig index 238dccfa76910..84653a823d3b0 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -405,6 +405,13 @@ config MMU_GATHER_NO_RANGE config HAVE_MMU_GATHER_NO_GATHER bool +config ARCH_WANT_IRQS_OFF_ACTIVATE_MM + bool + help + Temporary select until all architectures can be converted to have + irqs disabled over activate_mm. Architectures that do IPI based TLB + shootdowns should enable this. + config ARCH_HAVE_NMI_SAFE_CMPXCHG bool diff --git a/fs/exec.c b/fs/exec.c index de833553ae27d..2441eb1a1e2d0 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1044,11 +1044,24 @@ static int exec_mmap(struct mm_struct *mm) } task_lock(tsk); - active_mm = tsk->active_mm; membarrier_exec_mmap(mm); - tsk->mm = mm; + + local_irq_disable(); + active_mm = tsk->active_mm; tsk->active_mm = mm; + tsk->mm = mm; + /* + * This prevents preemption while active_mm is being loaded and + * it and mm are being updated, which could cause problems for + * lazy tlb mm refcounting when these are updated by context + * switches. Not all architectures can handle irqs off over + * activate_mm yet. + */ + if (!IS_ENABLED(CONFIG_ARCH_WANT_IRQS_OFF_ACTIVATE_MM)) + local_irq_enable(); activate_mm(active_mm, mm); + if (IS_ENABLED(CONFIG_ARCH_WANT_IRQS_OFF_ACTIVATE_MM)) + local_irq_enable(); tsk->mm->vmacache_seqnum = 0; vmacache_flush(tsk); task_unlock(tsk);