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=-13.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 BC57CC433DB for ; Wed, 13 Jan 2021 19:20:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5E9C722DFA for ; Wed, 13 Jan 2021 19:20:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728311AbhAMTUS (ORCPT ); Wed, 13 Jan 2021 14:20:18 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43706 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728227AbhAMTUR (ORCPT ); Wed, 13 Jan 2021 14:20:17 -0500 Received: from mail-ej1-x630.google.com (mail-ej1-x630.google.com [IPv6:2a00:1450:4864:20::630]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 44B15C061575 for ; Wed, 13 Jan 2021 11:19:37 -0800 (PST) Received: by mail-ej1-x630.google.com with SMTP id hs11so2360825ejc.1 for ; Wed, 13 Jan 2021 11:19:37 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=paul-moore-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=S/PHuWHTpBgQdNKFQVbdGCQEXvy7VZiLuqAEx0fTPmc=; b=tL+6Yn+IUsR2YEh35/aL3jXmHoQrvV8UasLgKQs0l8QTPelm18MXU0i3P5X+q4QWyq IhkiuKLuRQY4K2Bm+4ujxq41d+pjIeAoE7mCKTalqgNt447l7cBLfHL7p7cWpN6fvHsf MkfuWSXLj+eD22GOZPqCKgArFwovqD9oCbHS+/cDZVlW3quSi0wTe4iSNl4juLeRW3dP tZs7fPTeHCn3YCA5FgzY+0GRtINk3h4JiQd8M25jLQQoNIwHojUVEo3rFd4aIINQc7KR O94AirXCPjk3ria+0IeigE7amaEwrI5r79qJdIqrwqBuRbpYNY/1F+9qOtfE0tmo+l2Z N2Hw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=S/PHuWHTpBgQdNKFQVbdGCQEXvy7VZiLuqAEx0fTPmc=; b=A+7LnLaPLnanY4/J1gZtwg3SUrHn2sbT+SakIVu7u6XcNxuZS5mpOd2D/7EKQKLCyA T7wGUrmxDR1K0qMqCJ8KOHhFa6BdqWLhig5mhDm+KAI1RM1fe7xvYTpK6hoW7GLCfOUX XjpdhcGuMx07XHIOPXIufQOXNkSUR4QqKzVshF6Vzs0VH2yT99ulm0+Vqn9j4giNbxc8 7iLK7CrMPOIe7Jueihwn8FG7jX3dvVSt4j/L+gYTAA66oxKuTh3rXlpkwIoSv8hEpVS5 X8kZOVedemvo0mDNDTVyQ9wpgqDj6G+5OWpydkP7y/A4T9aUoU3R7mc9vzRXQW2zuMvZ SsqA== X-Gm-Message-State: AOAM533sq3pWWf2B3uYItclMdg6miB/XxqzEWYSxIq49bCgY9j4lLfsN IuJtYBBCAZkQ5Jxrqo360xxHg7gNbXPG9/uPiM3O X-Google-Smtp-Source: ABdhPJzpy46FnrM89yDbgKYDTI8w6gf3C22HrHYgT3GZAYPhAuzSu+VXCuKNthgyqqXgSQ08rYGZHUwVDEZ9CXerKRc= X-Received: by 2002:a17:907:4126:: with SMTP id mx6mr2618600ejb.91.1610565575830; Wed, 13 Jan 2021 11:19:35 -0800 (PST) MIME-Version: 1.0 References: <20210108040708.8389-1-tusharsu@linux.microsoft.com> <20210108040708.8389-9-tusharsu@linux.microsoft.com> <97328fc71687a0e1c327f6821548be9ba35bb193.camel@linux.ibm.com> In-Reply-To: <97328fc71687a0e1c327f6821548be9ba35bb193.camel@linux.ibm.com> From: Paul Moore Date: Wed, 13 Jan 2021 14:19:24 -0500 Message-ID: Subject: Re: [PATCH v10 8/8] selinux: include a consumer of the new IMA critical data hook To: Mimi Zohar Cc: Tushar Sugandhi , Stephen Smalley , casey@schaufler-ca.com, agk@redhat.com, snitzer@redhat.com, gmazyland@gmail.com, tyhicks@linux.microsoft.com, sashal@kernel.org, James Morris , nramas@linux.microsoft.com, linux-integrity@vger.kernel.org, selinux@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On Wed, Jan 13, 2021 at 2:13 PM Mimi Zohar wrote: > On Tue, 2021-01-12 at 11:27 -0500, Paul Moore wrote: > > On Thu, Jan 7, 2021 at 11:07 PM 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. > > > > > > 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 label=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 > > > Reviewed-by: Tyler Hicks > > > --- > > > Documentation/ABI/testing/ima_policy | 3 +- > > > security/selinux/Makefile | 2 + > > > security/selinux/ima.c | 64 ++++++++++++++++++++++++++++ > > > security/selinux/include/ima.h | 24 +++++++++++ > > > security/selinux/include/security.h | 3 +- > > > security/selinux/ss/services.c | 64 ++++++++++++++++++++++++---- > > > 6 files changed, 149 insertions(+), 11 deletions(-) > > > create mode 100644 security/selinux/ima.c > > > create mode 100644 security/selinux/include/ima.h > > > > I remain concerned about the possibility of bypassing a measurement by > > tampering with the time, but I appear to be the only one who is > > worried about this so I'm not going to block this patch on those > > grounds. > > > > Acked-by: Paul Moore > > Thanks, Paul. > > Including any unique string would cause the buffer hash to change, > forcing a new measurement. Perhaps they were concerned with > overflowing a counter. My understanding is that Lakshmi wanted to force a new measurement each time and felt using a timestamp would be the best way to do that. A counter, even if it wraps, would have a different value each time whereas a timestamp is vulnerable to time adjustments. While a properly controlled and audited system could be configured and monitored to detect such an event (I *think*), why rely on that if it isn't necessary? -- paul moore www.paul-moore.com