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Thu, 14 Jan 2021 02:49:12 +0000 Received: from d06av26.portsmouth.uk.ibm.com (d06av26.portsmouth.uk.ibm.com [9.149.105.62]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 10E2nAY244106238 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 14 Jan 2021 02:49:10 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6F425AE045; Thu, 14 Jan 2021 02:49:10 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BAFE7AE051; Thu, 14 Jan 2021 02:49:06 +0000 (GMT) Received: from li-f45666cc-3089-11b2-a85c-c57d1a57929f.ibm.com (unknown [9.160.57.196]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 14 Jan 2021 02:49:06 +0000 (GMT) Message-ID: <3746bc7673df25354411151442a7772b867be396.camel@linux.ibm.com> From: Mimi Zohar To: Paul Moore Date: Wed, 13 Jan 2021 21:49:05 -0500 In-Reply-To: References: <20210108040708.8389-1-tusharsu@linux.microsoft.com> <20210108040708.8389-9-tusharsu@linux.microsoft.com> <97328fc71687a0e1c327f6821548be9ba35bb193.camel@linux.ibm.com> <71cddb6c8676ccd63c89364d805cfca76d32cb6e.camel@linux.ibm.com> Mime-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343, 18.0.737 definitions=2021-01-13_14:2021-01-13, 2021-01-13 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 lowpriorityscore=0 mlxscore=0 spamscore=0 adultscore=0 bulkscore=0 priorityscore=1501 malwarescore=0 phishscore=0 mlxlogscore=999 clxscore=1015 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101140010 X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-loop: dm-devel@redhat.com Cc: sashal@kernel.org, dm-devel@redhat.com, snitzer@redhat.com, nramas@linux.microsoft.com, selinux@vger.kernel.org, Stephen Smalley , James Morris , linux-kernel@vger.kernel.org, casey@schaufler-ca.com, linux-security-module@vger.kernel.org, tyhicks@linux.microsoft.com, Tushar Sugandhi , linux-integrity@vger.kernel.org, gmazyland@gmail.com, agk@redhat.com Subject: Re: [dm-devel] [PATCH v10 8/8] selinux: include a consumer of the new IMA critical data hook X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dm-devel-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Wed, 2021-01-13 at 21:40 -0500, Paul Moore wrote: > On Wed, Jan 13, 2021 at 6:11 PM Mimi Zohar wrote: > > On Wed, 2021-01-13 at 17:10 -0500, Paul Moore wrote: > > > On Wed, Jan 13, 2021 at 4:11 PM Mimi Zohar wrote: > > > > On Wed, 2021-01-13 at 14:19 -0500, Paul Moore wrote: > > > > > 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? > > > > > > > > Why are you saying that even if the counter wraps a new measurement is > > > > guaranteed. I agree with the rest of what you said. > > > > > > I was assuming that the IMA code simply compares the passed > > > "policy_event_name" value to the previous value, if they are different > > > a new measurement is taken, if they are the same the measurement > > > request is ignored. If this is the case the counter value is only > > > important in as much as that it is different from the previous value, > > > even simply toggling a single bit back and forth would suffice in this > > > case. IMA doesn't keep a record of every previous "policy_event_name" > > > value does it? Am I misunderstanding how > > > ima_measure_critical_data(...) works? > > > > Originally, there was quite a bit of discussion as to how much or how > > little should be measured for a number of reasons. One reason is that > > the TPM is relatively slow. Another reason is to limit the size of the > > measurement list. For this reason, duplicate hashes aren't added to > > the measurement list or extended into the TPM. > > > > When a dentry is removed from cache, its also removed from IMA's iint > > cache. A subsequent file read would result in adding the measurement > > and extending the TPM again. ima_lookup_digest_entry() is called to > > prevent adding the duplicate entry. > > > > Lakshmi is trying to address the situation where an event changes a > > value, but then is restored to the original value. The original and > > subsequent events are measured, but restoring to the original value > > isn't re-measured. This isn't any different than when a file is > > modified and then reverted. > > > > Instead of changing the name like this, which doesn't work for files, > > allowing duplicate measurements should be generic, based on policy. > > Perhaps it is just the end of the day and I'm a bit tired, but I just > read all of the above and I have no idea what your current thoughts > are regarding this patch. Other than appending the timestamp, which is a hack, the patch is fine. Support for re-measuring an event can be upstreamed independently. Mimi -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel 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=-15.3 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,USER_AGENT_SANE_2 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 A69CBC433E6 for ; Thu, 14 Jan 2021 02:50:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7610B23602 for ; Thu, 14 Jan 2021 02:50:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727291AbhANCuD (ORCPT ); Wed, 13 Jan 2021 21:50:03 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:53352 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725888AbhANCuB (ORCPT ); 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Thu, 14 Jan 2021 02:49:10 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BAFE7AE051; Thu, 14 Jan 2021 02:49:06 +0000 (GMT) Received: from li-f45666cc-3089-11b2-a85c-c57d1a57929f.ibm.com (unknown [9.160.57.196]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 14 Jan 2021 02:49:06 +0000 (GMT) Message-ID: <3746bc7673df25354411151442a7772b867be396.camel@linux.ibm.com> Subject: Re: [PATCH v10 8/8] selinux: include a consumer of the new IMA critical data hook From: Mimi Zohar To: Paul Moore 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 Date: Wed, 13 Jan 2021 21:49:05 -0500 In-Reply-To: References: <20210108040708.8389-1-tusharsu@linux.microsoft.com> <20210108040708.8389-9-tusharsu@linux.microsoft.com> <97328fc71687a0e1c327f6821548be9ba35bb193.camel@linux.ibm.com> <71cddb6c8676ccd63c89364d805cfca76d32cb6e.camel@linux.ibm.com> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.28.5 (3.28.5-14.el8) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343,18.0.737 definitions=2021-01-13_14:2021-01-13,2021-01-13 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 lowpriorityscore=0 mlxscore=0 spamscore=0 adultscore=0 bulkscore=0 priorityscore=1501 malwarescore=0 phishscore=0 mlxlogscore=999 clxscore=1015 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101140010 Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On Wed, 2021-01-13 at 21:40 -0500, Paul Moore wrote: > On Wed, Jan 13, 2021 at 6:11 PM Mimi Zohar wrote: > > On Wed, 2021-01-13 at 17:10 -0500, Paul Moore wrote: > > > On Wed, Jan 13, 2021 at 4:11 PM Mimi Zohar wrote: > > > > On Wed, 2021-01-13 at 14:19 -0500, Paul Moore wrote: > > > > > 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? > > > > > > > > Why are you saying that even if the counter wraps a new measurement is > > > > guaranteed. I agree with the rest of what you said. > > > > > > I was assuming that the IMA code simply compares the passed > > > "policy_event_name" value to the previous value, if they are different > > > a new measurement is taken, if they are the same the measurement > > > request is ignored. If this is the case the counter value is only > > > important in as much as that it is different from the previous value, > > > even simply toggling a single bit back and forth would suffice in this > > > case. IMA doesn't keep a record of every previous "policy_event_name" > > > value does it? Am I misunderstanding how > > > ima_measure_critical_data(...) works? > > > > Originally, there was quite a bit of discussion as to how much or how > > little should be measured for a number of reasons. One reason is that > > the TPM is relatively slow. Another reason is to limit the size of the > > measurement list. For this reason, duplicate hashes aren't added to > > the measurement list or extended into the TPM. > > > > When a dentry is removed from cache, its also removed from IMA's iint > > cache. A subsequent file read would result in adding the measurement > > and extending the TPM again. ima_lookup_digest_entry() is called to > > prevent adding the duplicate entry. > > > > Lakshmi is trying to address the situation where an event changes a > > value, but then is restored to the original value. The original and > > subsequent events are measured, but restoring to the original value > > isn't re-measured. This isn't any different than when a file is > > modified and then reverted. > > > > Instead of changing the name like this, which doesn't work for files, > > allowing duplicate measurements should be generic, based on policy. > > Perhaps it is just the end of the day and I'm a bit tired, but I just > read all of the above and I have no idea what your current thoughts > are regarding this patch. Other than appending the timestamp, which is a hack, the patch is fine. Support for re-measuring an event can be upstreamed independently. Mimi