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=-20.4 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,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, 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 98B76C4346E for ; Thu, 24 Sep 2020 06:56:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 52E5A2395A for ; Thu, 24 Sep 2020 06:56:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="IAfJ9hUk" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727121AbgIXG4Q (ORCPT ); Thu, 24 Sep 2020 02:56:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44158 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727106AbgIXG4O (ORCPT ); Thu, 24 Sep 2020 02:56:14 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1C9C2C0613D3 for ; Wed, 23 Sep 2020 23:56:14 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id n13so1999012ybk.9 for ; Wed, 23 Sep 2020 23:56:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:in-reply-to:message-id:mime-version:references:subject :from:to:cc; bh=0lc69aA0lZ8Rvz8am0rRBV+yoECXRArvVbNXpFjuF40=; b=IAfJ9hUkQEx5zcT/VoPJFQBNov4n/VGUJ2rUk3yYjsbHcmOpHg2psmZnWDQT1HibG8 EoL1YHN1lh6kttKZYhxFxT/bhLxpS+FE5pJfN4nnr5ghPEoQFQX19vUBUc/UYBrd3aiD Y34qiKb+zTLH1vMmlVMKBg7iplLE/XMAYY4RDNo0HjImc21wcDBULe2M9Wu1rNNeJpNw OcyEND8JQgLZiLpqDHihBdOkCGy62BeywRwX0UGdoeAj+mEYZw+9IZ36lYOXp30qEtOe /3XOP5Wpdp9/In1hwPw11yVmfusFF4LGPB41iX8Pk1nN9EJL6Uygo8ox5pY8p2rh5ylP b1mQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=0lc69aA0lZ8Rvz8am0rRBV+yoECXRArvVbNXpFjuF40=; b=YdDO6p2KgdP/VsnM2NLzUtISY81jKfa8oK5MhWLkhweC/21Ij5rdLs55flEd2j0SDI ye6eme5YhIxwMraYeTiniGBpg5Hquyt5V2WN3WTJ8XhUl8MYW4/lokVEDJXRIJpg4gio rdGj89OcUl+xs0Kx4vjrJVXXxqNRfqjYP2oxjzVSi0Ih/XRmV/sXffPWGngBzWU8hKFg ru0nTOsttvMglxN9ZdqmopHNrvcxLwWRgxzljU0nyuuKuS25V+V43G2vt6A6RFsypkYa rgExaeqS4yWi2CNkW1EImx7olmpwtLmDa3yktyFtGsUeEJGwRTFYwlhoDFnNTInSW+MX lFyA== X-Gm-Message-State: AOAM531KmU3OoJL2l6tCVHXnkkGAwMbYscNyCGdUrl737js1If2TW+mU Cy9HwUGxtaaTKz9UHaPbkVQ0Q0nmuVBbdgx0pQ== X-Google-Smtp-Source: ABdhPJzMmPQPeoJFyWqE98eXL323QIE0VTj57+sU2UBDWAcdC/qsoSA0OeELDrbSu6EGODdQw9UHozulqnwRgeyFRA== 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:a5b:e83:: with SMTP id z3mr4661708ybr.289.1600930573277; Wed, 23 Sep 2020 23:56:13 -0700 (PDT) Date: Wed, 23 Sep 2020 23:56:05 -0700 In-Reply-To: <20200924065606.3351177-1-lokeshgidra@google.com> Message-Id: <20200924065606.3351177-2-lokeshgidra@google.com> Mime-Version: 1.0 References: <20200924065606.3351177-1-lokeshgidra@google.com> X-Mailer: git-send-email 2.28.0.681.g6f77f65b4e-goog Subject: [PATCH v4 1/2] Add UFFD_USER_MODE_ONLY 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 , Daniel Colascione Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org userfaultfd handles page faults from both user and kernel code. Add a new UFFD_USER_MODE_ONLY flag for userfaultfd(2) that makes the resulting userfaultfd object refuse to handle faults from kernel mode, treating these faults as if SIGBUS were always raised, causing the kernel code to fail with EFAULT. A future patch adds a knob allowing administrators to give some processes the ability to create userfaultfd file objects only if they pass UFFD_USER_MODE_ONLY, reducing the likelihood that these processes will exploit userfaultfd's ability to delay kernel page faults to open timing windows for future exploits. Signed-off-by: Daniel Colascione Signed-off-by: Lokesh Gidra --- fs/userfaultfd.c | 6 +++++- include/uapi/linux/userfaultfd.h | 9 +++++++++ 2 files changed, 14 insertions(+), 1 deletion(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 0e4a3837da52..3191434057f3 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -405,6 +405,9 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason) if (ctx->features & UFFD_FEATURE_SIGBUS) goto out; + if ((vmf->flags & FAULT_FLAG_USER) == 0 && + ctx->flags & UFFD_USER_MODE_ONLY) + goto out; /* * If it's already released don't get it. This avoids to loop @@ -1975,10 +1978,11 @@ SYSCALL_DEFINE1(userfaultfd, int, flags) BUG_ON(!current->mm); /* Check the UFFD_* constants for consistency. */ + BUILD_BUG_ON(UFFD_USER_MODE_ONLY & UFFD_SHARED_FCNTL_FLAGS); BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC); BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK); - if (flags & ~UFFD_SHARED_FCNTL_FLAGS) + if (flags & ~(UFFD_SHARED_FCNTL_FLAGS | UFFD_USER_MODE_ONLY)) return -EINVAL; ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL); diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h index e7e98bde221f..5f2d88212f7c 100644 --- a/include/uapi/linux/userfaultfd.h +++ b/include/uapi/linux/userfaultfd.h @@ -257,4 +257,13 @@ struct uffdio_writeprotect { __u64 mode; }; +/* + * Flags for the userfaultfd(2) system call itself. + */ + +/* + * Create a userfaultfd that can handle page faults only in user mode. + */ +#define UFFD_USER_MODE_ONLY 1 + #endif /* _LINUX_USERFAULTFD_H */ -- 2.28.0.681.g6f77f65b4e-goog