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=-11.2 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL autolearn=no 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 927E5C433E0 for ; Tue, 22 Dec 2020 00:25:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 65AD022B51 for ; Tue, 22 Dec 2020 00:25:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726105AbgLVAZ1 (ORCPT ); Mon, 21 Dec 2020 19:25:27 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51274 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725985AbgLVAZY (ORCPT ); Mon, 21 Dec 2020 19:25:24 -0500 Received: from mail-il1-x133.google.com (mail-il1-x133.google.com [IPv6:2607:f8b0:4864:20::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 668C1C0613D6 for ; Mon, 21 Dec 2020 16:24:44 -0800 (PST) Received: by mail-il1-x133.google.com with SMTP id v3so10516705ilo.5 for ; Mon, 21 Dec 2020 16:24:44 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=4RuWWi7Zl0r6VeRFf6xBa4XAn38HB/limrAzhvwBg9E=; b=QxNJ3YhgavKUMBo9RFOSja6zyVmlQSaT9lxfBxy2MZqCO+Lmri5ACNMvgW/1nEBH9u RfRWRqk4hPOPoCizuEb4pvXMgwxOT3Yp0Ue0HSEN8FP5649e+o8It9Pp1hTl/gncEv5v Z5XKcfOnokS7rz2lbhVKUIcP2ImTJdgDicSI+Z0xj3sYdg/tR7EHorMT2UyccQToc2tL dZtFjPlW8euhQGfmx+x3tDQOdffJLed1RX3ZpyaPAhpRQKIWopoqX2NIU02F98qrQMxd xlOKdL4kia4rVg4CK34oJd0QGnOYYHaaNyiItjcwMmIrOmZiqy+eN8lQ16fg7OCSigBx XeIA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=4RuWWi7Zl0r6VeRFf6xBa4XAn38HB/limrAzhvwBg9E=; b=XLSCuO74bPbAB/ahGTGqKkKCU+/EFfFA55jjQ0oCwAUnfqQeODfl3Lt/V7V0C0v+tK NBo2c4wWBvSHjWou74eMUj+oUfQovpYWr2mo7QtTRfvumHs5xhFs/ivZrhBNswbuUDRi u7KnS1NKrHulPJEz1ARImR6Nye/07weg2mFhIG5awg8IAMWW8hGCMWm0Px0RrwSnByR1 2s2OgeXRt/tQQWYZ+9EOn0c/pDnIU4TGORxnA76eXbx2YVE9bflGhQhriNCTUzYRUE9r ah75Iw8FO5pqgeSeQ+hlGjqrFRYaMpMNPPf2v9azXGrcK3MbqspFnPFEDbVcvaxduy0P Hhvw== X-Gm-Message-State: AOAM5323OAqIKNtHEcXUM85399PDQiY2HDHV0WUvhI/YOYuEGgryUUQX dx157mET6DbWQ5KXiGDX6GSUNQ== X-Google-Smtp-Source: ABdhPJyBEsQhZx/Eo+G0MR8uYZv1+RPEAPRNQ3dCCuOdkBFw/mpJJCIkxzG9Yzm/uczjOmTQpWBxzA== X-Received: by 2002:a92:9ada:: with SMTP id c87mr18944102ill.5.1608596683475; Mon, 21 Dec 2020 16:24:43 -0800 (PST) Received: from google.com ([2620:15c:183:200:7220:84ff:fe09:2d90]) by smtp.gmail.com with ESMTPSA id w9sm14146363ilq.43.2020.12.21.16.24.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Dec 2020 16:24:42 -0800 (PST) Date: Mon, 21 Dec 2020 17:24:38 -0700 From: Yu Zhao To: Linus Torvalds Cc: Peter Xu , Nadav Amit , Andrea Arcangeli , linux-mm , lkml , Pavel Emelyanov , Mike Kravetz , Mike Rapoport , stable , Minchan Kim , Andy Lutomirski , Will Deacon , Peter Zijlstra Subject: Re: [PATCH] mm/userfaultfd: fix memory corruption due to writeprotect Message-ID: References: <9E301C7C-882A-4E0F-8D6D-1170E792065A@gmail.com> <1FCC8F93-FF29-44D3-A73A-DF943D056680@gmail.com> <20201221223041.GL6640@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 21, 2020 at 04:11:01PM -0800, Linus Torvalds wrote: > On Mon, Dec 21, 2020 at 4:00 PM Yu Zhao wrote: > > > > My first instinct is to be conservative and revert 09854ba94c6a ("mm: > > do_wp_page() simplification") so people are less likely to come back > > and complain about performance issues from holding mmap lock for > > write when clearing pte_write. > > Well, the thing is, that simplificaiton was actually part of fixing a > real regression wrt GUP. > > Reverting that would break a308c71bf1e6 ("mm/gup: Remove enfornced COW > mechanism"). > > And that one was the (better) fix for commit 17839856fd58 that fixed a > real security issue, but did it with a big hammer that then caused > problems for uffd-wp (and some other loads). There's a bit more > context in the merge message in commit b25d1dc9474e Merge branch > 'simplify-do_wp_page'. > > So while that commit 09854ba94c6a on its own is "just" a > simplification, it's actually part of a bigger series that fixes > serious problems. > > Linus Well, that settles it then. I don't any better idea that is as safe as what Nadav has.