From patchwork Wed Aug 26 01:39:57 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lokesh Gidra X-Patchwork-Id: 11737055 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 26991722 for ; Wed, 26 Aug 2020 01:40:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0DA632072D for ; Wed, 26 Aug 2020 01:40:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=google.com header.i=@google.com header.b="EONDCuS+" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726599AbgHZBkH (ORCPT ); Tue, 25 Aug 2020 21:40:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52676 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726711AbgHZBkF (ORCPT ); Tue, 25 Aug 2020 21:40:05 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2DADCC061756 for ; Tue, 25 Aug 2020 18:40:04 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id x6so742451ybp.10 for ; Tue, 25 Aug 2020 18:40:04 -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=5gbbSEIbK4yWfAq5tI3QZ5QR0T3vBYa40yqv00FjnKE=; b=EONDCuS+3d189+D8AI/ERnlF2MPUIT7CBrakxJTU20KFNPZczvwfsf1FS7U8Zf4ab7 RLTnMSpLwpGgvo9sEQb4SABuuS8pidp1RWTGa6ZtAZp9jBilnvom2oWEtMAtK8g9iQ/4 TwhmyRdfMWBu8+9tQlT2FA6xDjRZ1Uv1DM1L4vIQz0LhLMj72Swg6ag5Oj4MkhE90jsI LQrA7K4nJV480H+LBMNtxrYT8HvxiZCHIfLE73B6gTp7oPCvXkoTXz5lSwmJ+T2UY4vW +afTo7Jj4t7u/TZGLO+qfjQBwfh19BzspsByBUfGZNEiUg7JUgj9917P0P1DFTJ6MqFQ p80A== 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=5gbbSEIbK4yWfAq5tI3QZ5QR0T3vBYa40yqv00FjnKE=; b=U4PChdBmIiAuGnaPYPbzXzhgSfxmNlsEEk/d0/PW85qdsBTb5Rnj/jbmLKV6QavnXC zOALtzuE57bFilmRGjz02zKnjwphuXlAHgvGZyzWftrxjxohsI7HJz9wN+nQG59TFAmR dVhtfGzdL3WgC2nn/JlMUVnkaFxA+kJ8u/EMj4QEXq/kTMtIUw2a9BHdWct1pFy2biOB ctxufh8E2H1Clv/ignPZSX87Gr6/ZDy/iwiwqfrg+DEExhxmpQ9x/tad5AxgGEfC2RoP OuMyrUmddjGTwUHr8TFoqtJfsvDChJSY41x54MLsJKs09QFbb8yXb/sqVyedf+148fx2 7tjQ== X-Gm-Message-State: AOAM5322d+miePU55LhgRqZgNXcokrPu+wxK1bfhzyr+Kfp4ut/iJPSY nrhtMYsfj7B/T3Nri9ntypHgwU91O1esPDcXzg== X-Google-Smtp-Source: ABdhPJxGz/85hOODz7qBm7E2cIdEfrCvaBHLShAkLac9WkQj0OvIYzr7pzQHum6uPD4aip5+AhIe/HXpy8UENxoUeg== X-Received: from lg.mtv.corp.google.com ([2620:15c:211:202:f693:9fff:fef4:29dd]) (user=lokeshgidra job=sendgmr) by 2002:a25:7643:: with SMTP id r64mr20062213ybc.109.1598406003331; Tue, 25 Aug 2020 18:40:03 -0700 (PDT) Date: Tue, 25 Aug 2020 18:39:57 -0700 Message-Id: <20200826013959.1981270-1-lokeshgidra@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.28.0.297.g1956fa8f8d-goog Subject: [PATCH v3 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 Sender: linux-fsdevel-owner@vger.kernel.org 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 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 | 10 +++++++--- fs/userfaultfd.c | 16 +++++++++++++--- include/uapi/linux/userfaultfd.h | 9 +++++++++ kernel/sysctl.c | 2 +- 4 files changed, 30 insertions(+), 7 deletions(-)