From patchwork Wed Apr 11 16:25:18 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Howells X-Patchwork-Id: 10335835 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 8426E602D8 for ; Wed, 11 Apr 2018 16:29:59 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 71DCC204BD for ; Wed, 11 Apr 2018 16:29:59 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 66B1E20700; Wed, 11 Apr 2018 16:29:59 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00, MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id E113D204BD for ; Wed, 11 Apr 2018 16:29:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752906AbeDKQZW (ORCPT ); Wed, 11 Apr 2018 12:25:22 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:45148 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752804AbeDKQZU (ORCPT ); Wed, 11 Apr 2018 12:25:20 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 159298182D1C; Wed, 11 Apr 2018 16:25:20 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-120-8.rdu2.redhat.com [10.10.120.8]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3EA68215CDAF; Wed, 11 Apr 2018 16:25:19 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH 06/24] kexec_load: Disable at runtime if the kernel is locked down From: David Howells To: torvalds@linux-foundation.org Cc: linux-man@vger.kernel.org, linux-api@vger.kernel.org, jmorris@namei.org, linux-kernel@vger.kernel.org, dhowells@redhat.com, linux-security-module@vger.kernel.org Date: Wed, 11 Apr 2018 17:25:18 +0100 Message-ID: <152346391877.4030.6270466586590461223.stgit@warthog.procyon.org.uk> In-Reply-To: <152346387861.4030.4408662483445703127.stgit@warthog.procyon.org.uk> References: <152346387861.4030.4408662483445703127.stgit@warthog.procyon.org.uk> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Wed, 11 Apr 2018 16:25:20 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Wed, 11 Apr 2018 16:25:20 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'dhowells@redhat.com' RCPT:'' Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: X-Virus-Scanned: ClamAV using ClamSMTP From: Matthew Garrett The kexec_load() syscall permits the loading and execution of arbitrary code in ring 0, which is something that lock-down is meant to prevent. It makes sense to disable kexec_load() in this situation. This does not affect kexec_file_load() syscall which can check for a signature on the image to be booted. Signed-off-by: Matthew Garrett Signed-off-by: David Howells Acked-by: Dave Young Reviewed-by: "Lee, Chun-Yi" Reviewed-by: James Morris cc: kexec@lists.infradead.org Nacked-by: "Eric W. Biederman" --- kernel/kexec.c | 7 +++++++ 1 file changed, 7 insertions(+) -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/kernel/kexec.c b/kernel/kexec.c index aed8fb2564b3..1553ac765e73 100644 --- a/kernel/kexec.c +++ b/kernel/kexec.c @@ -199,6 +199,13 @@ static inline int kexec_load_check(unsigned long nr_segments, if (!capable(CAP_SYS_BOOT) || kexec_load_disabled) return -EPERM; + /* + * kexec can be used to circumvent module loading restrictions, so + * prevent loading in that case + */ + if (kernel_is_locked_down("kexec of unsigned images")) + return -EPERM; + /* * Verify we have a legal set of flags * This leaves us room for future extensions.