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=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,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 0DAD4C388F9 for ; Fri, 20 Nov 2020 03:04:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9B2ED2237B for ; Fri, 20 Nov 2020 03:04:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="bn7ilro4" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727076AbgKTDEV (ORCPT ); Thu, 19 Nov 2020 22:04:21 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39200 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726988AbgKTDEU (ORCPT ); Thu, 19 Nov 2020 22:04:20 -0500 Received: from mail-qv1-xf49.google.com (mail-qv1-xf49.google.com [IPv6:2607:f8b0:4864:20::f49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D308CC0613CF for ; Thu, 19 Nov 2020 19:04:19 -0800 (PST) Received: by mail-qv1-xf49.google.com with SMTP id 5so6135369qvk.3 for ; Thu, 19 Nov 2020 19:04:19 -0800 (PST) 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=S80ppjIa8avRgCLzMtS9uD6gmPO2GY129S5ovczlpcA=; b=bn7ilro4cOy+tDQBg0BRd9vDaADZLaBkGp8sycj7nJbZrcIxlJ8zRDBvHRXiSp4/vt bCGgK1DJGcSDZjcdWvldVAXk1Kr4M9ydE7q4MBcnvrbaj3SY1Xn3DjskcExrURpmNq/u /k9u5/4jdFDvoWSgxZ2b3dJmKDyDIz+KCQ6ri9RfFSySl2P/JzZddjgT6ZDBZYmIJwZj ySNIw9IdveLjnuXgBiEIlp0j10K5uwBXgUIhyff9SIXaEBmLNkopb1NZwpYFoVrcOe5I VqjQGTivND7CdMI4ftMS3HLMtAfS4yOPIVF/Qu8baAHx6XAhDLquEzfKJT0HkGoDhjEj mXDw== 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=S80ppjIa8avRgCLzMtS9uD6gmPO2GY129S5ovczlpcA=; b=HUU7IPJ+pG3oqwysmyyFjdoxHSRuM5BWPzqqUUQ+3S5IsduwGHYlerGLeNUraKxGS8 H9mx5ON9Afe6laDvoTLZI1X2YFa9nAOc6qIEtmDW85GhqTPZW+oTcuOXWULVPOYvM8RK YOAG7EJEUBaIZmRiLTwmpkXVPauFD1Z+U8xLpsyXvjMwPiB0UYC8ChABlE5W9a7SsUS/ AUAS9/9GEoMHImowEv6X7zfiWqJ9mEk0jeoyQxcTPMRIVHT2Kc9tLVAzBGVK8yOPD/Qe 22t9zSPGZDO7z+IWgsuE+wIq9RNYhZSZ2u4mAkCaeVAnCMXyZkVXv40G/U1ZBJC/vw9H GJGw== X-Gm-Message-State: AOAM530c+8BYQ2Zbye+7HWFHs4ezAiulquH4AVAVTJApdWlmccJep3+b CCIJgUewfQjNYe+pwYEZmI9VNdLdUffLM8C7ew== X-Google-Smtp-Source: ABdhPJx34e9nPiDw+gT8zarXTKmsqrTynJL70oY3j/bY/HhHf4bACXfvvpHHXZO8YLCgaXOcRpzYo2Ixc5atUVGxXA== Sender: "lokeshgidra via sendgmr" X-Received: from lg.mtv.corp.google.com ([100.89.4.209]) (user=lokeshgidra job=sendgmr) by 2002:ad4:4051:: with SMTP id r17mr10076025qvp.39.1605841458917; Thu, 19 Nov 2020 19:04:18 -0800 (PST) Date: Thu, 19 Nov 2020 19:04:10 -0800 In-Reply-To: <20201120030411.2690816-1-lokeshgidra@google.com> Message-Id: <20201120030411.2690816-2-lokeshgidra@google.com> Mime-Version: 1.0 References: <20201120030411.2690816-1-lokeshgidra@google.com> X-Mailer: git-send-email 2.29.2.454.gaff20da3a2-goog Subject: [PATCH v6 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, 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, 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 Reviewed-by: Andrea Arcangeli --- fs/userfaultfd.c | 10 +++++++++- include/uapi/linux/userfaultfd.h | 9 +++++++++ 2 files changed, 18 insertions(+), 1 deletion(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 000b457ad087..605599fde015 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -405,6 +405,13 @@ 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) { + printk_once(KERN_WARNING "uffd: Set unprivileged_userfaultfd " + "sysctl knob to 1 if kernel faults must be handled " + "without obtaining CAP_SYS_PTRACE capability\n"); + goto out; + } /* * If it's already released don't get it. This avoids to loop @@ -1965,10 +1972,11 @@ 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 */ -- 2.29.0.rc1.297.gfa9743e501-goog