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=-14.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT, 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 A8EB1C43457 for ; Sun, 11 Oct 2020 06:25:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 72FE3207FB for ; Sun, 11 Oct 2020 06:25:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="sWYTJbGO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726858AbgJKGZB (ORCPT ); Sun, 11 Oct 2020 02:25:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54016 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726719AbgJKGZB (ORCPT ); Sun, 11 Oct 2020 02:25:01 -0400 Received: from mail-qt1-x84a.google.com (mail-qt1-x84a.google.com [IPv6:2607:f8b0:4864:20::84a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E266BC0613D2 for ; Sat, 10 Oct 2020 23:25:00 -0700 (PDT) Received: by mail-qt1-x84a.google.com with SMTP id y53so10321567qth.2 for ; Sat, 10 Oct 2020 23:25:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:message-id:mime-version:subject:from:to:cc; bh=UJx97gIPGIXFXkRks4Wo0vV6Q6PxKBpX120vcE6WJsg=; b=sWYTJbGOpsmE70syYCNzGsAplxbAsaDGvmNcakNaECKP+Ez8bD3Rdi6wI3rU59lXC9 6gfqTcuW9qjebxjGoE/SlnfNpby5Lx9LohoeIR0wNuoONARjym5sepDDSAAzRvXJTOvh jWgsUd7YnS0HYTD/FqQ5fTCIc4Egy70KtDZFi4GTlSgAJR+du+MoKKkmnVxmYz+VjXsm /LRCyixeYm3wQkxoj7oL5e4ruFzoYKC/W4hO6hQ+Fby9VjHr2ghxh2G+ODkOMtdkOl2L n/3z5bO46TzAHYpXmxMlyLX3xSV5i+mcGQEM8lPmKs5wXtRt8EL6d6bXbmBDWTELZFnI Xcjw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:message-id:mime-version:subject:from :to:cc; bh=UJx97gIPGIXFXkRks4Wo0vV6Q6PxKBpX120vcE6WJsg=; b=WTMIhB+fTEksAxnosQggCcpM6lh/B8Tf+TSwcoDoYpLCuWc+G6BH0ZSgafrXF4uswX gqXiR8ERN6qjH+Y4wegaUvlCe7AumENIdyCUnOw2gvXXK6EeARzplYU9VhDjTMLOSTRL jGAtfNXkHuUrWEGoDMf/BqbkFt8Nhbu6FRq7sNgc1EWMgXMwWOSpiWb4EMRlu4fRNKGc CzeC97mrbsdXuI9E+6GjMpFoN7FBCm+XobcwsEc7RQMJW6QuE2XHYXGTB5bVkyGxHfQ9 UY0SO43VVHw+uCNJ9HNuWoEO/jNaewiOXZtXgN6pGeehZ9QLB5unsaOi3kEykAyxfMK7 Lg2g== X-Gm-Message-State: AOAM5311glPUGSsJSuKF2ydrEn2P+oCZFS96QTd3TngAMBnO2VGAcCdB d7gZ8LPice5xjbj2kkGvXosiz+CZKvmzJ6bD8g== X-Google-Smtp-Source: ABdhPJwwuHEwTJas51CDs0CXwMgtZ6GF8BpLVVQwMWpZxEVKux8CKK116qNPOrQYZazm9+cW7Nre45/LrKMgXOFtEA== Sender: "lokeshgidra via sendgmr" X-Received: from lg.mtv.corp.google.com ([2620:15c:211:202:f693:9fff:fef4:29dd]) (user=lokeshgidra job=sendgmr) by 2002:a0c:a203:: with SMTP id f3mr20270612qva.33.1602397499810; Sat, 10 Oct 2020 23:24:59 -0700 (PDT) Date: Sat, 10 Oct 2020 23:24:54 -0700 Message-Id: <20201011062456.4065576-1-lokeshgidra@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.28.0.1011.ga647a8990f-goog Subject: [PATCH v5 0/2] Control over userfaultfd kernel-fault handling From: Lokesh Gidra To: Kees Cook , Jonathan Corbet , Peter Xu , Andrea Arcangeli , Sebastian Andrzej Siewior , Andrew Morton Cc: Alexander Viro , Stephen Smalley , Eric Biggers , Lokesh Gidra , Daniel Colascione , "Joel Fernandes (Google)" , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kaleshsingh@google.com, calin@google.com, surenb@google.com, nnk@google.com, jeffv@google.com, kernel-team@android.com, Mike Rapoport , Shaohua Li , Jerome Glisse , Mauro Carvalho Chehab , Johannes Weiner , Mel Gorman , Nitin Gupta , Vlastimil Babka , Iurii Zaikin , Luis Chamberlain Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patch series is split from [1]. The other series enables SELinux support for userfaultfd file descriptors so that its creation and movement can be controlled. It has been demonstrated on various occasions that suspending kernel code execution for an arbitrary amount of time at any access to userspace memory (copy_from_user()/copy_to_user()/...) can be exploited to change the intended behavior of the kernel. For instance, handling page faults in kernel-mode using userfaultfd has been exploited in [2, 3]. Likewise, FUSE, which is similar to userfaultfd in this respect, has been exploited in [4, 5] for similar outcome. This small patch series adds a new flag to userfaultfd(2) that allows callers to give up the ability to handle kernel-mode faults with the resulting UFFD file object. It then adds a 'user-mode only' option to the unprivileged_userfaultfd sysctl knob to require unprivileged callers to use this new flag. The purpose of this new interface is to decrease the chance of an unprivileged userfaultfd user taking advantage of userfaultfd to enhance security vulnerabilities by lengthening the race window in kernel code. [1] https://lore.kernel.org/lkml/20200211225547.235083-1-dancol@google.com/ [2] https://duasynt.com/blog/linux-kernel-heap-spray [3] https://duasynt.com/blog/cve-2016-6187-heap-off-by-one-exploit [4] https://googleprojectzero.blogspot.com/2016/06/exploiting-recursion-in-linux-kernel_20.html [5] https://bugs.chromium.org/p/project-zero/issues/detail?id=808 Changes since v4: - Added warning when bailing out from handling kernel fault. Changes since v3: - Modified the meaning of value '0' of unprivileged_userfaultfd sysctl knob. Setting this knob to '0' now allows unprivileged users to use userfaultfd, but can handle page faults in user-mode only. - The default value of unprivileged_userfaultfd sysctl knob is changed to '0'. Changes since v2: - Removed 'uffd_flags' and directly used 'UFFD_USER_MODE_ONLY' in userfaultfd(). Changes since v1: - Added external references to the threats from allowing unprivileged users to handle page faults from kernel-mode. - Removed the new sysctl knob restricting handling of page faults from kernel-mode, and added an option for the same in the existing 'unprivileged_userfaultfd' knob. Lokesh Gidra (2): Add UFFD_USER_MODE_ONLY Add user-mode only option to unprivileged_userfaultfd sysctl knob Documentation/admin-guide/sysctl/vm.rst | 15 ++++++++++----- fs/userfaultfd.c | 16 +++++++++++++--- include/uapi/linux/userfaultfd.h | 9 +++++++++ 3 files changed, 32 insertions(+), 8 deletions(-) -- 2.28.0.1011.ga647a8990f-goog