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=-21.2 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=unavailable 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 D0D84C388F9 for ; Fri, 20 Nov 2020 03:04:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 700C02223F for ; Fri, 20 Nov 2020 03:04:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="BLljEWyf" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726985AbgKTDES (ORCPT ); Thu, 19 Nov 2020 22:04:18 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39190 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726494AbgKTDES (ORCPT ); Thu, 19 Nov 2020 22:04:18 -0500 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 B1514C0617A7 for ; Thu, 19 Nov 2020 19:04:16 -0800 (PST) Received: by mail-yb1-xb49.google.com with SMTP id w8so10121150ybq.4 for ; Thu, 19 Nov 2020 19:04:16 -0800 (PST) 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=8XFAGaMnZpaYT0ztE4+ED+zm8jGUSJs5c4zzKttTIPI=; b=BLljEWyfBU6MrGtybZ+HWm2CfYE4oGLcD3L+xxb5kEOx5ilALIDKkVQlH6oubTxp6L BBZTmpiz8uXxqqtHEhsFdDU6VTag6k3qtgSbyzUTrbxcEKDWDv3nuTYOQcqxDG2+Luqu Y7mZURx+7aeBj5HvS8JuF4nSnoJ4X/RwElcATSf8h99LbSpkeq0mE+wSYWodCBJn09aV zuF0FtCgIwr/ukk1vgBu+9GsvQo+vBe7TqF4dmSd+e62WwwIhb/of9is4L7vqWxZEM7h fLD1Dh8hjkGCpDCiJn42Ntat0/VIFIOfI0GG3hwN9iaO7eVyfAAQPb3lcs9mcrRDzhBy LNxw== 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=8XFAGaMnZpaYT0ztE4+ED+zm8jGUSJs5c4zzKttTIPI=; b=ELStRSjDPiixhZeHvBg6GqeBvbWylGTInTxgpe21YK9fwULiFZyFY0w2OR/6fVUUz2 fNBudTvygb0t0y2JHpSGdToUvzdL9KET1y6l0qqq4Xmx9ulInIh4qJhN9JogFBdiR0wy JcNUZQ9qEMJw8XIfW544qP5EPZuUC31bdNbnQiFHIcrjUDcIaAgiR7arFYDTuD/UDqv2 6YcLZhaEH/y3BRLur+mLaOytkMZ2uTduvjCzC8FOWt1IurI7dlC5WK7UKRSP4/tryFIx lri8f/QyJBdjRGDw3bz00WSOxCV/3d1iS/d/1GTtjNQFj1QDpL/1jmw/KnCPX+2cucDX U5pA== X-Gm-Message-State: AOAM533umFelDooCCOsCd20H0rcoAAsHWGbVW9Ysr3bSgnST5RbioRZE xTlWlP0RijRW5U3GfBo5uivM1HOBsFSkJ7OXHA== X-Google-Smtp-Source: ABdhPJyzXLRqU2uLJ4PTem5aB9mGgB98rkzGCcOgbzeOlWOc4omKQdbXxNUk7El2Ic8Wjh8MK4DlbpnhP3swOgdDAA== Sender: "lokeshgidra via sendgmr" X-Received: from lg.mtv.corp.google.com ([100.89.4.209]) (user=lokeshgidra job=sendgmr) by 2002:a25:abea:: with SMTP id v97mr16686450ybi.275.1605841455790; Thu, 19 Nov 2020 19:04:15 -0800 (PST) Date: Thu, 19 Nov 2020 19:04:09 -0800 Message-Id: <20201120030411.2690816-1-lokeshgidra@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.29.2.454.gaff20da3a2-goog Subject: [PATCH v6 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, 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 , linux-mm@kvack.kernel.org 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 v5: - Added printk_once when unprivileged_userfaultfd is set to 0 and userfaultfd syscall is called without UFFD_USER_MODE_ONLY in the absence of CAP_SYS_PTRACE capability. 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 | 20 +++++++++++++++++--- include/uapi/linux/userfaultfd.h | 9 +++++++++ 3 files changed, 36 insertions(+), 8 deletions(-) -- 2.29.0.rc1.297.gfa9743e501-goog