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=-12.3 required=3.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED,DKIM_INVALID,DKIM_SIGNED,FREEMAIL_FORGED_FROMDOMAIN, FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 5F32DC433E2 for ; Fri, 28 Aug 2020 10:00:40 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 236EE2078A for ; Fri, 28 Aug 2020 10:00:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="CQod5hZ8" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 236EE2078A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id BF84D6B000C; Fri, 28 Aug 2020 06:00:39 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BAA4C8D0002; Fri, 28 Aug 2020 06:00:39 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id ABF6A8D0001; Fri, 28 Aug 2020 06:00:39 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0082.hostedemail.com [216.40.44.82]) by kanga.kvack.org (Postfix) with ESMTP id 9528B6B000C for ; Fri, 28 Aug 2020 06:00:39 -0400 (EDT) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 63C89ABF7 for ; Fri, 28 Aug 2020 10:00:39 +0000 (UTC) X-FDA: 77199532998.11.space37_16107b227074 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin11.hostedemail.com (Postfix) with ESMTP id 24087180F8B82 for ; Fri, 28 Aug 2020 10:00:39 +0000 (UTC) X-HE-Tag: space37_16107b227074 X-Filterd-Recvd-Size: 6928 Received: from mail-pf1-f196.google.com (mail-pf1-f196.google.com [209.85.210.196]) by imf40.hostedemail.com (Postfix) with ESMTP for ; Fri, 28 Aug 2020 10:00:38 +0000 (UTC) Received: by mail-pf1-f196.google.com with SMTP id k15so391436pfc.12 for ; Fri, 28 Aug 2020 03:00:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=PMGQxaBKPbON3ssZWMqrEm63rTUeWUDOhP6COLqPYSc=; b=CQod5hZ8nMSXxmoYAACVHF/qI22QxGeFSjZUjfpoMAoBOV9QseFdRM4mT4eXynXUTC Srct4/znp2udP6D2fWV0bzQ+pU+XXOtJaMi2g+drMUXj2K60C7ryDET6zClkdldor8i/ E7b0vIa8R3BWPgXPD+PJJc+AOPD+vqs7DgiqbTvdaT+K3ptqwzdJmNc9JYAun+j0QBae 7AboNgbfU8v9VPxj5nmgHoLhu4gnUy6QW/u+UtbhElPKKl+uWSB8sno/j9ZONdogYAlc aQLufAMyCIBONhDco8RGsYXEqd6c77U8MUJIv054R9Y1Pl38buDYzYUONBBZjC6y1qyg Lk4g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=PMGQxaBKPbON3ssZWMqrEm63rTUeWUDOhP6COLqPYSc=; b=kG9RdUTHLL1Hjc9tmBOD58d15Oyltexj41sxA1ElRhj7b5J/UM+u9sBNThFd1Au2r0 HUhYfjb0MOzCbctCWTVKP7wo6ezdVken3kFJuOKJqWMkw2fuv6ydEL0YlrK1gEuAhgYL UlTH3nWBviO+ZLUskhqZQC7OccIDIA7QZtJDFoSPiMnlJZ0yGML0k7Lpgiyho8+X8/Yw bJE4Qq3c9qG9XA8AvKN1sYaQAcnBmjk1rSwZ4GV9aNw3Wi36s0NV34xQAHKB2mN47RAy //fTfbWywuMM/soI85OpNvw0MVXBXwvrBooF8nnedCMPECdPlq2FOnLzSVDcKm088S1u vTHQ== X-Gm-Message-State: AOAM5310K4jtVa0MnjseKHV4GdvgqBYs0u7HlbHlILDLYomgUDEnfB/1 bb700/F4uwS/3AQAkQYiPhGM6pt/+es= X-Google-Smtp-Source: ABdhPJzJadmdcr+E5dPdAeWoEtRrezvpoEws2ofoV8cHCzMpxKfGsMWs/5DPALVlJiaUIB6ACL7lKA== X-Received: by 2002:aa7:96f4:: with SMTP id i20mr619172pfq.312.1598608837398; Fri, 28 Aug 2020 03:00:37 -0700 (PDT) Received: from bobo.ozlabs.ibm.com (61-68-212-105.tpgi.com.au. [61.68.212.105]) by smtp.gmail.com with ESMTPSA id 78sm1068608pfv.200.2020.08.28.03.00.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Aug 2020 03:00:37 -0700 (PDT) From: Nicholas Piggin To: linux-mm@kvack.org Cc: Nicholas Piggin , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, "Aneesh Kumar K.V" , Andrew Morton , Jens Axboe , Peter Zijlstra , "David S. Miller" Subject: [PATCH 1/4] mm: fix exec activate_mm vs TLB shootdown and lazy tlb switching race Date: Fri, 28 Aug 2020 20:00:19 +1000 Message-Id: <20200828100022.1099682-2-npiggin@gmail.com> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20200828100022.1099682-1-npiggin@gmail.com> References: <20200828100022.1099682-1-npiggin@gmail.com> MIME-Version: 1.0 X-Rspamd-Queue-Id: 24087180F8B82 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 =3D current->mm; active_mm =3D current->active_mm; *** preempt *** --------------------> schedule() prev->active_mm =3D NULL; mmdrop(prev active_mm); ... <-------------------- schedule() current->mm =3D mm; current->active_mm =3D 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 --- arch/Kconfig | 7 +++++++ fs/exec.c | 17 +++++++++++++++-- 2 files changed, 22 insertions(+), 2 deletions(-) diff --git a/arch/Kconfig b/arch/Kconfig index af14a567b493..94821e3f94d1 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -414,6 +414,13 @@ config MMU_GATHER_NO_GATHER bool depends on MMU_GATHER_TABLE_FREE =20 +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 =20 diff --git a/fs/exec.c b/fs/exec.c index a91003e28eaa..d4fb18baf1fb 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1130,11 +1130,24 @@ static int exec_mmap(struct mm_struct *mm) } =20 task_lock(tsk); - active_mm =3D tsk->active_mm; membarrier_exec_mmap(mm); - tsk->mm =3D mm; + + local_irq_disable(); + active_mm =3D tsk->active_mm; tsk->active_mm =3D mm; + tsk->mm =3D 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 =3D 0; vmacache_flush(tsk); task_unlock(tsk); --=20 2.23.0