From patchwork Sun Oct 11 06:24:55 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lokesh Gidra X-Patchwork-Id: 11830677 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 3226B174A 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 16EF420795 for ; Sun, 11 Oct 2020 06:25:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="LVXko3Hc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727008AbgJKGZE (ORCPT ); Sun, 11 Oct 2020 02:25:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54034 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726898AbgJKGZD (ORCPT ); Sun, 11 Oct 2020 02:25:03 -0400 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 BA1F7C0613D2 for ; Sat, 10 Oct 2020 23:25:03 -0700 (PDT) Received: by mail-qv1-xf49.google.com with SMTP id eh4so4870465qvb.12 for ; Sat, 10 Oct 2020 23:25:03 -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=EOovoB63mTNgnDeBGShd0QgMbi9PshapUqeSaojca1c=; b=LVXko3Hcrxqpkqjw4qp3l2lqDGjuJbCxZwlPQHlN3ABbKQE5MnJQJGYvrPrzp0+XQJ xe35ME2rFCaVv6FCK8RBf96ywpGvNTtsbOgMFmcsifDgIDsJYxLffmrAJLgPe04ITLhP 7q7V3YPlWvaRT8l/h21YGG8ykaEMDOJrVf7fa4Ogu7ZBflNc0n3VGKRQUato1UY9JDCz 9awfqjwCrbO7YZWSEu12mT6XSBJNXvsdCK2YM2TRriD/nL1oskRfAYOVUiLoz1mXdluR R0BzQdOraoC1ywdVMUmzqmwmIKhxYEJMbfUIrEp1IjVUgpvuHVfJlp28ySs9B/AhhGcv uF7A== 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=EOovoB63mTNgnDeBGShd0QgMbi9PshapUqeSaojca1c=; b=rMuiwor8MlICv3uVnsqM+/U6JoLvWcmErSjOFyibODHNDU0+DVvH1jO6gEYUKiNcPN zPqWMBgdMIsd2nHsUPqKBxSXAwVZKSTNgwripYldjZl8I+JHIcsOql8zrrGmLodoP2Yu LgurE9yyTFHTksGCikc9uGsTExJiV4u/YkflQqPpNmrZns3Qp6vyxqyD59ATQNmqyVVF gqkgthje1Eb74RxxJEJQYS4g8nFbn6PrX0TaZnFzBRcdwjGbUvTLJUG9sK4gntw0+Dvt LPirL18VuNwV3VkdzzJLCpAi7MyaJ/hM5d789aAdc9PbJiAPN1+LefSC75l8yY8SoxNx tNHQ== X-Gm-Message-State: AOAM533oD4SYpOPym46AXhLKzp7I+EWwyKejiUbsjQQF9sEuZJVOpMkE +6VyJdG+rbsXeyiqINkZsP48skiz2QEnGyCByQ== X-Google-Smtp-Source: ABdhPJw9sm8/WVHSmcrHkJYm7Ha57Yv6FZUh8ylmPOpg1TPvFBMEVR2+aHjracYoglMHkrUriRfoN2WmW7juJLjHwA== 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:ad4:544a:: with SMTP id h10mr20428528qvt.35.1602397502814; Sat, 10 Oct 2020 23:25:02 -0700 (PDT) Date: Sat, 10 Oct 2020 23:24:55 -0700 In-Reply-To: <20201011062456.4065576-1-lokeshgidra@google.com> Message-Id: <20201011062456.4065576-2-lokeshgidra@google.com> Mime-Version: 1.0 References: <20201011062456.4065576-1-lokeshgidra@google.com> X-Mailer: git-send-email 2.28.0.1011.ga647a8990f-goog Subject: [PATCH v5 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 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@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 0e4a3837da52..bd229f06d4e9 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 @@ -1975,10 +1982,11 @@ 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 */