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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 B3180C433E6 for ; Tue, 22 Dec 2020 00:12:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 86FC122AED for ; Tue, 22 Dec 2020 00:12:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727091AbgLVAMD (ORCPT ); Mon, 21 Dec 2020 19:12:03 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49254 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725783AbgLVAMC (ORCPT ); Mon, 21 Dec 2020 19:12:02 -0500 Received: from mail-lf1-x131.google.com (mail-lf1-x131.google.com [IPv6:2a00:1450:4864:20::131]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D2064C0613D6 for ; Mon, 21 Dec 2020 16:11:21 -0800 (PST) Received: by mail-lf1-x131.google.com with SMTP id m25so27795464lfc.11 for ; Mon, 21 Dec 2020 16:11:21 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=hTuaw61/vu6Ch8LghemKyv8ZjkRGc9Bd4nL0SHS84i8=; b=XRqPvAjqNYfYvdTAPbyVeX/6O742pr4s6sQMYn9OH27FKmpUFDXDQcK9Tl2txOM6YO vqCZR/1DVmPxmcBQfj8ygABjF6pmB8V6dG3OaZcI7+9pJSjvqpbcqzrEpWL97R7G4EDm qS6LzBxmqQ8dWZpVnIRQLX6xY4Ofvg3UtYHJE= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=hTuaw61/vu6Ch8LghemKyv8ZjkRGc9Bd4nL0SHS84i8=; b=oVKmEuhZk1HLuRK+sOP2i85Lye+IN9qu1P8Wlt6KCU4t4PP8NAeQJ7dDqoFv0Mi0sj PJG2oLA7LwTvkw648utP6RHGqYKf/uLiTH7ur4MBvnhmooKcoZlp12+Tr3aA6qQvbFYS z8GtNwGBvVKgoVEFdkOh5b0Ya1/r5L0LL/G8xUcOquw94399/eoJsXrTo+cdWFHUfcSW YsiIch4VBmqpYgd5KR9j+FxUbQOUIx321hMW65yqj1u1Lhv6SR8haatnr3+kt4c0UuwN SUl25tdhP6xV0Lr2RpLkbg2ULnqt3jEdCvX3HkIhoAVlHxUCcOzErhZJuY5B1I2q6/21 Wxbw== X-Gm-Message-State: AOAM532RovPWvleieHlHQpWVJUqeQr/ZO2I/BbmGNSd+Rzq/Ff9rMPiV V0XIuq2LgirKH1d2erfmiUhPQ0OeUNRqkA== X-Google-Smtp-Source: ABdhPJwWEcgkz3m1P7Jph0GqQIOwcg0VPDNDUGQTP6VS+DAzqPvq4JhyCXeOqqLYo+SW4SHiPXk8YA== X-Received: by 2002:a05:6512:108a:: with SMTP id j10mr7609677lfg.381.1608595879913; Mon, 21 Dec 2020 16:11:19 -0800 (PST) Received: from mail-lf1-f47.google.com (mail-lf1-f47.google.com. [209.85.167.47]) by smtp.gmail.com with ESMTPSA id h13sm2321309lfj.110.2020.12.21.16.11.18 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 21 Dec 2020 16:11:18 -0800 (PST) Received: by mail-lf1-f47.google.com with SMTP id o17so27916415lfg.4 for ; Mon, 21 Dec 2020 16:11:18 -0800 (PST) X-Received: by 2002:ac2:41d9:: with SMTP id d25mr7001569lfi.377.1608595877900; Mon, 21 Dec 2020 16:11:17 -0800 (PST) MIME-Version: 1.0 References: <76B4F49B-ED61-47EA-9BE4-7F17A26B610D@gmail.com> <9E301C7C-882A-4E0F-8D6D-1170E792065A@gmail.com> <1FCC8F93-FF29-44D3-A73A-DF943D056680@gmail.com> <20201221223041.GL6640@xz-x1> In-Reply-To: From: Linus Torvalds Date: Mon, 21 Dec 2020 16:11:01 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] mm/userfaultfd: fix memory corruption due to writeprotect To: Yu Zhao 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 Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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