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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 31F3EC4332F for ; Thu, 10 Nov 2022 15:18:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231468AbiKJPSk (ORCPT ); Thu, 10 Nov 2022 10:18:40 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34512 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231222AbiKJPSJ (ORCPT ); Thu, 10 Nov 2022 10:18:09 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1628B1F2D9 for ; Thu, 10 Nov 2022 07:17:09 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1668093428; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Ff4uIKDwEIX1/MsTGENOmYM+Xv3Uc0BmHEC53Fnq3vY=; b=cOuv3RLAxaFsMmREF/kybouKR8goDi+OUvGXNAJvH/nzfaK8kTTZ74xPedRNWnm5I+teuR 8+LAzb6wBAjyvEzhos6pyEoryWqiwPmMB5clAH249cQH3LLPtywesuquoS5YXY05SUQL6I YHU17qBj15/lDEHRHzxNSnIbfkjeccQ= Received: from mail-qt1-f197.google.com (mail-qt1-f197.google.com [209.85.160.197]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-73-g_wJ1O3SPMWm9ZRVZBR7xA-1; Thu, 10 Nov 2022 10:17:07 -0500 X-MC-Unique: g_wJ1O3SPMWm9ZRVZBR7xA-1 Received: by mail-qt1-f197.google.com with SMTP id n12-20020ac85a0c000000b003a5849497f9so1560119qta.20 for ; Thu, 10 Nov 2022 07:17:06 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=Ff4uIKDwEIX1/MsTGENOmYM+Xv3Uc0BmHEC53Fnq3vY=; b=tRqKjxBgo5FJsy94vKnQbGcxlew0wzyYEpjcR4Fvz5nnbYIto4d+JsCJ9xblGuqIRM 4bAccc+57OEpB9SYGRq3EUAi1LtFe9ceFN6EPH71ygh3QDUwVlH7+YZ9aPvbxR7YRlPN 2ZMhJHsK0lQ9YqZeqMD75o8g47qJ2FAODWajj6lKpe/7dav+ToCbqLOgpETBF1XUIlvB r1p+PlcUwApZZg/huXTj5htrtzDsarK/SJWGlDDaLZwfTbVyqWy6qZpUiUYHiC1hiG4U eLJH2zuemp8Dy6W0QP/L/i4wMmizaTJ0Zca160kNFXl7ZI7HiVv9z8DjA6/vgxLMSF0V FlWg== X-Gm-Message-State: ACrzQf2AhuPwB5E+/OEeiTf00WMh8qWCDu+QZm03Io7BnE85SlDu//qd H7Bi/e9SAtddy5mwvfKs57F7aQxtu+GUCmJit+OPzCIDnfaHr8HSMyaqtJ7wZfnTz/EFp0sT8ww oB61cRQWFlWzXnkREI6Mg8o81 X-Received: by 2002:ac8:688b:0:b0:3a5:4032:84 with SMTP id m11-20020ac8688b000000b003a540320084mr38891962qtq.594.1668093426511; Thu, 10 Nov 2022 07:17:06 -0800 (PST) X-Google-Smtp-Source: AMsMyM6tpasQ30d/7Z7xCvuxHK3YLAF5URmUDDJQLgiiIm9IreU3H5TqEwrf6XMfeWsh8URcfVsH1A== X-Received: by 2002:ac8:688b:0:b0:3a5:4032:84 with SMTP id m11-20020ac8688b000000b003a540320084mr38891929qtq.594.1668093426204; Thu, 10 Nov 2022 07:17:06 -0800 (PST) Received: from x1n.redhat.com (bras-base-aurron9127w-grc-46-70-31-27-79.dsl.bell.ca. [70.31.27.79]) by smtp.gmail.com with ESMTPSA id l19-20020a05620a28d300b006ec771d8f89sm13621596qkp.112.2022.11.10.07.17.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Nov 2022 07:17:05 -0800 (PST) From: Peter Xu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Mike Rapoport , peterx@redhat.com, Nadav Amit , Andrew Morton , Axel Rasmussen , Andrea Arcangeli , Ives van Hoorne , stable@vger.kernel.org Subject: [PATCH 1/2] mm/migrate: Fix read-only page got writable when recover pte Date: Thu, 10 Nov 2022 10:17:01 -0500 Message-Id: <20221110151702.1478763-2-peterx@redhat.com> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20221110151702.1478763-1-peterx@redhat.com> References: <20221110151702.1478763-1-peterx@redhat.com> MIME-Version: 1.0 Content-type: text/plain Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ives van Hoorne from codesandbox.io reported an issue regarding possible data loss of uffd-wp when applied to memfds on heavily loaded systems. The sympton is some read page got data mismatch from the snapshot child VMs. Here I can also reproduce with a Rust reproducer that was provided by Ives that keeps taking snapshot of a 256MB VM, on a 32G system when I initiate 80 instances I can trigger the issues in ten minutes. It turns out that we got some pages write-through even if uffd-wp is applied to the pte. The problem is, when removing migration entries, we didn't really worry about write bit as long as we know it's not a write migration entry. That may not be true, for some memory types (e.g. writable shmem) mk_pte can return a pte with write bit set, then to recover the migration entry to its original state we need to explicit wr-protect the pte or it'll has the write bit set if it's a read migration entry. For uffd it can cause write-through. I didn't verify, but I think it'll be the same for mprotect()ed pages and after migration we can miss the sigbus instead. The relevant code on uffd was introduced in the anon support, which is commit f45ec5ff16a7 ("userfaultfd: wp: support swap and page migration", 2020-04-07). However anon shouldn't suffer from this problem because anon should already have the write bit cleared always, so that may not be a proper Fixes target. To satisfy the need on the backport, I'm attaching the Fixes tag to the uffd-wp shmem support. Since no one had issue with mprotect, so I assume that's also the kernel version we should start to backport for stable, and we shouldn't need to worry before that. Cc: Andrea Arcangeli Cc: stable@vger.kernel.org Fixes: b1f9e876862d ("mm/uffd: enable write protection for shmem & hugetlbfs") Reported-by: Ives van Hoorne Signed-off-by: Peter Xu --- mm/migrate.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/mm/migrate.c b/mm/migrate.c index dff333593a8a..8b6351c08c78 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -213,8 +213,14 @@ static bool remove_migration_pte(struct folio *folio, pte = pte_mkdirty(pte); if (is_writable_migration_entry(entry)) pte = maybe_mkwrite(pte, vma); - else if (pte_swp_uffd_wp(*pvmw.pte)) + else + /* NOTE: mk_pte can have write bit set */ + pte = pte_wrprotect(pte); + + if (pte_swp_uffd_wp(*pvmw.pte)) { + WARN_ON_ONCE(pte_write(pte)); pte = pte_mkuffd_wp(pte); + } if (folio_test_anon(folio) && !is_readable_migration_entry(entry)) rmap_flags |= RMAP_EXCLUSIVE; -- 2.37.3