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=-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 3CBDAC388F9 for ; Tue, 3 Nov 2020 20:39:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 023A22224E for ; Tue, 3 Nov 2020 20:39:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604435963; bh=AzMRPgqKbqAe9ZcEx1rFOKZyF/Yw9jFgRDrZoNw+Yw4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=G2cxY2U/0aHIDyjisq4h5fqllY+LXJvcqIB9EH6PfL7YYHQv7hG6lxStWvfk9PnfO GWTYynvP3YHNeEMfzdrAp9ipTH/aHn3XRldEmaK0KykuJbFdr1KL1TFSS+aPbwoStW 15viKqSOhnUvWhN/HYkKBbRiGLY9RB9eh4qh6CjE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729213AbgKCUjT (ORCPT ); Tue, 3 Nov 2020 15:39:19 -0500 Received: from mail.kernel.org ([198.145.29.99]:49718 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730057AbgKCUjC (ORCPT ); Tue, 3 Nov 2020 15:39:02 -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 40B92223AC; Tue, 3 Nov 2020 20:39:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604435941; bh=AzMRPgqKbqAe9ZcEx1rFOKZyF/Yw9jFgRDrZoNw+Yw4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=gOQaZ/1LChTVSlhPyzq2gKl1iBBO7H7bQlpEP8osfklFvMdqYAF+hZnmoOYtT3lHz aid2VeVdW/D15OoDOxTzJ52AF8LHKNw6Ol4MKL+Ml6JzwlYuS7k0bqauBYo56F86sr +0AXs9B6sBiuuGLh1zGoI+qXTU12SOqAbLJSKgOk= 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 5.9 048/391] mm: fix exec activate_mm vs TLB shootdown and lazy tlb switching race Date: Tue, 3 Nov 2020 21:31:39 +0100 Message-Id: <20201103203350.784148375@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201103203348.153465465@linuxfoundation.org> References: <20201103203348.153465465@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 af14a567b493f..94821e3f94d16 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -414,6 +414,13 @@ config MMU_GATHER_NO_GATHER bool depends on MMU_GATHER_TABLE_FREE +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 07910f5032e74..3622681489864 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1131,11 +1131,24 @@ 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); -- 2.27.0