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=-24.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1,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 92A95C4361B for ; Sat, 12 Dec 2020 00:49:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 59E1F2336F for ; Sat, 12 Dec 2020 00:49:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2437744AbgLLAfN (ORCPT ); Fri, 11 Dec 2020 19:35:13 -0500 Received: from linux.microsoft.com ([13.77.154.182]:59364 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2407332AbgLLAei (ORCPT ); Fri, 11 Dec 2020 19:34:38 -0500 Received: from [192.168.0.104] (c-73-42-176-67.hsd1.wa.comcast.net [73.42.176.67]) by linux.microsoft.com (Postfix) with ESMTPSA id B971820B7189; Fri, 11 Dec 2020 16:33:56 -0800 (PST) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com B971820B7189 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1607733237; bh=VZNQa3qRPgUnre55aohRTEHVjzAlSRRySxISovoGzSk=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=ExyALXf6MqtM3DX6EahqceWf1wvpmYO1ObxwoHMKGHdASDgz4FOUIVUcYB4Mifm5T TTL5TrShUAm48D6m0Do6D6fNXqywe9ZJnCnQGS8/M6HxN87vZtEejhdT7SKD91oSUP FLZV5B1dOul2CLKtLB4ZxwqBqLPgD6+S4v/F9se4= Subject: Re: [PATCH v8 8/8] selinux: include a consumer of the new IMA critical data hook To: Tyler Hicks , Tushar Sugandhi Cc: zohar@linux.ibm.com, stephen.smalley.work@gmail.com, casey@schaufler-ca.com, agk@redhat.com, snitzer@redhat.com, gmazyland@gmail.com, paul@paul-moore.com, sashal@kernel.org, jmorris@namei.org, linux-integrity@vger.kernel.org, selinux@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com References: <20201211235807.30815-1-tusharsu@linux.microsoft.com> <20201211235807.30815-9-tusharsu@linux.microsoft.com> <20201212003215.GG4951@sequoia> From: Lakshmi Ramasubramanian Message-ID: <09c3b609-eacb-86e1-b130-cf1dbf4852b8@linux.microsoft.com> Date: Fri, 11 Dec 2020 16:33:56 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201212003215.GG4951@sequoia> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/11/20 4:32 PM, Tyler Hicks wrote: > On 2020-12-11 15:58:07, Tushar Sugandhi wrote: >> From: Lakshmi Ramasubramanian >> >> SELinux stores the active policy in memory, so the changes to this data >> at runtime would have an impact on the security guarantees provided >> by SELinux. Measuring in-memory SELinux policy through IMA subsystem >> provides a secure way for the attestation service to remotely validate >> the policy contents at runtime. >> >> Measure the hash of the loaded policy by calling the IMA hook >> ima_measure_critical_data(). Since the size of the loaded policy can >> be large (several MB), measure the hash of the policy instead of >> the entire policy to avoid bloating the IMA log entry. >> >> Add "selinux" to the list of supported data sources maintained by IMA >> to enable measuring SELinux data. >> >> To enable SELinux data measurement, the following steps are required: >> >> 1, Add "ima_policy=critical_data" to the kernel command line arguments >> to enable measuring SELinux data at boot time. >> For example, >> BOOT_IMAGE=/boot/vmlinuz-5.10.0-rc1+ root=UUID=fd643309-a5d2-4ed3-b10d-3c579a5fab2f ro nomodeset security=selinux ima_policy=critical_data >> >> 2, Add the following rule to /etc/ima/ima-policy >> measure func=CRITICAL_DATA data_source=selinux >> >> Sample measurement of the hash of SELinux policy: >> >> To verify the measured data with the current SELinux policy run >> the following commands and verify the output hash values match. >> >> sha256sum /sys/fs/selinux/policy | cut -d' ' -f 1 >> >> grep "selinux-policy-hash" /sys/kernel/security/integrity/ima/ascii_runtime_measurements | tail -1 | cut -d' ' -f 6 >> >> Note that the actual verification of SELinux policy would require loading >> the expected policy into an identical kernel on a pristine/known-safe >> system and run the sha256sum /sys/kernel/selinux/policy there to get >> the expected hash. >> >> Signed-off-by: Lakshmi Ramasubramanian >> Suggested-by: Stephen Smalley > > This looks good but I've got one small suggestion below if you roll a > v9. Feel free to add: > > Reviewed-by: Tyler Hicks > >> diff --git a/security/selinux/measure.c b/security/selinux/measure.c >> new file mode 100644 >> index 000000000000..a070d8dae403 >> --- /dev/null >> +++ b/security/selinux/measure.c >> @@ -0,0 +1,81 @@ >> +// SPDX-License-Identifier: GPL-2.0-or-later >> +/* >> + * Measure SELinux state using IMA subsystem. >> + */ >> +#include >> +#include >> +#include >> +#include "security.h" >> + >> +/* >> + * This function creates a unique name by appending the timestamp to >> + * the given string. This string is passed as "event_name" to the IMA >> + * hook to measure the given SELinux data. >> + * >> + * The data provided by SELinux to the IMA subsystem for measuring may have >> + * already been measured (for instance the same state existed earlier). >> + * But for SELinux the current data represents a state change and hence >> + * needs to be measured again. To enable this, pass a unique "event_name" >> + * to the IMA hook so that IMA subsystem will always measure the given data. >> + * >> + * For example, >> + * At time T0 SELinux data to be measured is "foo". IMA measures it. >> + * At time T1 the data is changed to "bar". IMA measures it. >> + * At time T2 the data is changed to "foo" again. IMA will not measure it >> + * (since it was already measured) unless the event_name, for instance, >> + * is different in this call. >> + */ >> +static char *selinux_event_name(const char *name_prefix) >> +{ >> + char *event_name = NULL; >> + struct timespec64 cur_time; >> + >> + ktime_get_real_ts64(&cur_time); >> + event_name = kasprintf(GFP_KERNEL, "%s-%lld:%09ld", name_prefix, >> + cur_time.tv_sec, cur_time.tv_nsec); >> + return event_name; > > There's no longer a need to store the return of kasprintf() in a > variable. Just 'return kasprint(...);' and get rid of the event_name > variable. > Sure - I'll make the change. -lakshmi