From patchwork Thu Sep 24 06:56:04 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lokesh Gidra X-Patchwork-Id: 11796379 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id CC3906CA for ; Thu, 24 Sep 2020 06:56:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A88872395C for ; Thu, 24 Sep 2020 06:56:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="A6fOq1HO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727105AbgIXG4O (ORCPT ); Thu, 24 Sep 2020 02:56:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44144 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727090AbgIXG4L (ORCPT ); Thu, 24 Sep 2020 02:56:11 -0400 Received: from mail-pg1-x54a.google.com (mail-pg1-x54a.google.com [IPv6:2607:f8b0:4864:20::54a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EE086C0613D3 for ; Wed, 23 Sep 2020 23:56:10 -0700 (PDT) Received: by mail-pg1-x54a.google.com with SMTP id 82so1504329pgf.16 for ; Wed, 23 Sep 2020 23:56:10 -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=FX0p/GcmPpR3We5nTHUDyc9BUTZhvYJ9+N0VF4ja3D0=; b=A6fOq1HOlUuYS2ejjODUD35m8TFnAilniB8q/he/79yXRI6J7NI/5Ni7kHBCvEkC2m lcXuePvKeAjjCDD7fCMEPX38aVIXcuUWP+W4OMSy0zBk2sxHJx8ra7LETRsT0HIRDyye xSwf61KUpd7wPrXq18JauwkfZwXsMB8awli9ljDrb5XWJlKwH3mlcV56ZLOVPibIG4Ic o/eVdv/JTMLjilq0gn9LEnIdeugRCiuR9+nExc8TyYrfq2ju1CexD/xlhgumusLgQp7o XRzmYIJmWMncSaLiHbfMQfFKTa0htqvMutDnKpI3x/vLO5QTmvQvgoeB0YAL5ijGpOW3 0CmQ== 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=FX0p/GcmPpR3We5nTHUDyc9BUTZhvYJ9+N0VF4ja3D0=; b=QA4VtlW7ze5r+cAK8I/3F2dkSfQsKfHsI6/OUR3rvk4z2S9PasrFJWDCLhSxTVTkGD DiQegxb5o2/+3nKBiTcBTw8b2BtgCvsMJL9hyO5awe0c29aROfyHyBN0I6d+csz7kXzb L5yjpW+oWSoAQeVI0hJ28R5yzEMLV8EwgWRgp8aro8KatpLkB4Mj21Zq4EGXA8yu44Lh l8rSB9UXn3aK1LSdh4x186n/yPtvpgjbd9SCUpNULU04PmkltA+Gqb169QFo4ABSp0FH Aae0V+vxPrsboFcTghT4ZNNQT3Q+a6IWaTdn08QO/zGngVHNqMqP0LqGI0daiouOQwKz PCJQ== X-Gm-Message-State: AOAM533pJyKpycF1sjm6EDrkmhMw48dm7u4UnaYMGvuiZZn8QwKVdgC8 menIFSJkJgFd7fcuR6obwfnXTpbogSDTFs0F3A== X-Google-Smtp-Source: ABdhPJwhRa38PHwfQdB4AKI0fOgdNDJYzEpWP8u7QkJdKT8QhABjPf/lE453ktfsBvnzt0vFPv5CAiF1JPyJRhzdTA== 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:a17:902:82c2:b029:d1:f36a:ab97 with SMTP id u2-20020a17090282c2b02900d1f36aab97mr3356719plz.64.1600930570089; Wed, 23 Sep 2020 23:56:10 -0700 (PDT) Date: Wed, 23 Sep 2020 23:56:04 -0700 Message-Id: <20200924065606.3351177-1-lokeshgidra@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.28.0.681.g6f77f65b4e-goog Subject: [PATCH v4 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 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@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 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 | 12 +++++++++--- include/uapi/linux/userfaultfd.h | 9 +++++++++ 3 files changed, 28 insertions(+), 8 deletions(-)