From patchwork Sun Oct 11 06:24:54 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lokesh Gidra X-Patchwork-Id: 11830675 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 0EDF115E6 for ; Sun, 11 Oct 2020 06:25:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DDDFD20795 for ; Sun, 11 Oct 2020 06:25:20 +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 S1726761AbgJKGZB (ORCPT ); Sun, 11 Oct 2020 02:25:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54012 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725882AbgJKGZB (ORCPT ); Sun, 11 Oct 2020 02:25:01 -0400 Received: from mail-qt1-x849.google.com (mail-qt1-x849.google.com [IPv6:2607:f8b0:4864:20::849]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D7700C0613CE for ; Sat, 10 Oct 2020 23:25:00 -0700 (PDT) Received: by mail-qt1-x849.google.com with SMTP id l12so10237983qtu.22 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=ZngxjSFd5RxBhXWinrJ1j/AruujHd8BVVDk4csiwirarzoxmpncnqBmUhSrLvhNWeU UAedpS+Qr/vqdodKXW9kNbpn3qgjVfUEWVPQAdB0jK4sbs12n5toUbo+9PXiTiTL7Yb5 zkdKF4aQBRcPTDp7JO1hNKe3FcG4iVKQWfX+86uuPx9N9+uJ1AcuB1Wl4eGyO2z1Q0DK VFmjmROXumQO++pYWz15+jbgLTErWJN9Kd86uRkNXFROQ8KpWyLnBI14HCC/Sp0drVdV XwD0Z1R7/jJ31kTOnQJ07gaNhqcbN8yJXOEmLRs7lXwc+ywwmsYpdpvxJnczkLWz7Rvs DnxA== X-Gm-Message-State: AOAM533wSEGM6IAFEseYuGJU14iNFAuU73dzELh1QHBiMkuDFqmrcO2i fuqpGynl9ptGmDNnYACe1D3RW3aCirqZBptKMQ== 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 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 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(-)