From patchwork Wed Nov 4 01:14:06 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Michael Ellerman X-Patchwork-Id: 316741 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,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 30C9AC388F7 for ; Wed, 4 Nov 2020 01:14:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B068E223EA for ; Wed, 4 Nov 2020 01:14:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ellerman.id.au header.i=@ellerman.id.au header.b="ibXCrtZz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730176AbgKDBOS (ORCPT ); Tue, 3 Nov 2020 20:14:18 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35142 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729144AbgKDBOS (ORCPT ); Tue, 3 Nov 2020 20:14:18 -0500 Received: from ozlabs.org (ozlabs.org [IPv6:2401:3900:2:1::2]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DFB2BC040203; Tue, 3 Nov 2020 17:14:17 -0800 (PST) Received: by ozlabs.org (Postfix, from userid 1034) id 4CQpZv09RBz9sT6; Wed, 4 Nov 2020 12:14:14 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ellerman.id.au; s=201909; t=1604452455; bh=L9+aN6uN2wgac4rv/jHRrYhBNqmampUYZI4+b+mvtBY=; h=From:To:Cc:Subject:Date:From; b=ibXCrtZzs7jfeUQi/EC7Dj82Al1W+o0KGfOhSNW+CvlQ7SP5aW0R67XglvUj1o/+u l5sQxbrX5SdrAtw4IlYSUJHPScXYDgY98UtKip7Yg901AA1OBcdfnz4GdeoXTNjV6x YARGmI6w+xg9i/zBM2cHwdp1xBLH69fptx4KSJzWgzX3yUe26LFiXaaCikYTJjrD3L w40EWyAGHEZwilJvm//WEZiEJ0o6l5HsAEpEDa5dOBhXNTYl0haYAGpRLgyc7ibi29 6H8Vk7am17V1ytAnGeZwyNm+N3luO+ge6TDMxjn6d0/podAJGNzMgL4feNCfzg0/gf /t6LnuL2wJIJQ== From: Michael Ellerman To: stable@vger.kernel.org Cc: linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org, npiggin@gmail.com, gregkh@linuxfoundation.org, peterz@infradead.org Subject: [PATCH 4.19] mm: fix exec activate_mm vs TLB shootdown and lazy tlb switching race Date: Wed, 4 Nov 2020 12:14:06 +1100 Message-Id: <20201104011406.598487-1-mpe@ellerman.id.au> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Nicholas Piggin commit d53c3dfb23c45f7d4f910c3a3ca84bf0a99c6143 upstream. 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) [mpe: Manual backport to 4.19 due to membarrier_exec_mmap(mm) changes] Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200914045219.3736466-2-npiggin@gmail.com --- arch/Kconfig | 7 +++++++ fs/exec.c | 15 ++++++++++++++- 2 files changed, 21 insertions(+), 1 deletion(-) diff --git a/arch/Kconfig b/arch/Kconfig index a336548487e6..e3a030f7a722 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -366,6 +366,13 @@ config HAVE_RCU_TABLE_FREE config HAVE_RCU_TABLE_INVALIDATE 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 cece8c14f377..52788644c4af 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1028,10 +1028,23 @@ static int exec_mmap(struct mm_struct *mm) } } task_lock(tsk); + + local_irq_disable(); active_mm = tsk->active_mm; - tsk->mm = 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);