Message-ID: <5a8c8801-d8ce-ab9b-3d38-25fbb4a4f6bb@linux.ibm.com>
Date:   Thu, 2 Dec 2021 13:03:03 -0500
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.2.0
Subject: Re: [RFC 08/20] ima: Move measurement list related variables into
 ima_namespace
Content-Language: en-US
To:     jejb@linux.ibm.com, linux-integrity@vger.kernel.org
Cc:     zohar@linux.ibm.com, serge@hallyn.com,
        christian.brauner@ubuntu.com, containers@lists.linux.dev,
        dmitry.kasatkin@gmail.com, ebiederm@xmission.com,
        krzysztof.struczynski@huawei.com, roberto.sassu@huawei.com,
        mpeters@redhat.com, lhinds@redhat.com, lsturman@redhat.com,
        puiterwi@redhat.com, jamjoom@us.ibm.com,
        linux-kernel@vger.kernel.org, paul@paul-moore.com, rgb@redhat.com,
        linux-security-module@vger.kernel.org, jmorris@namei.org
References: <20211130160654.1418231-1-stefanb@linux.ibm.com>
 <20211130160654.1418231-9-stefanb@linux.ibm.com>
 <141ce433f026b47edb1d9a8f89e4581db253c579.camel@linux.ibm.com>
 <c3b99439-1dd6-e204-ad41-5d8bacb54d48@linux.ibm.com>
 <eeaadc76ca2da67d79c155497a73c6905b70e726.camel@linux.ibm.com>
 <05da6ebc-0cd4-753a-8589-4b1a06d198c6@linux.ibm.com>
 <39e43a4829b86b5a87bc082628cc6f45d4d8c899.camel@linux.ibm.com>
From:   Stefan Berger <stefanb@linux.ibm.com>
In-Reply-To: <39e43a4829b86b5a87bc082628cc6f45d4d8c899.camel@linux.ibm.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 12/2/21 12:44, James Bottomley wrote:
> On Thu, 2021-12-02 at 11:45 -0500, Stefan Berger wrote:
>> On 12/2/21 11:29, James Bottomley wrote:
>>> On Thu, 2021-12-02 at 08:41 -0500, Stefan Berger wrote:
>>>> On 12/2/21 07:46, James Bottomley wrote:
>>>>> On Tue, 2021-11-30 at 11:06 -0500, Stefan Berger wrote:
>>>>>> Move measurement list related variables into the
>>>>>> ima_namespace.
>>>>>> This
>>>>>> way a
>>>>>> front-end like SecurityFS can show the measurement list
>>>>>> inside an
>>>>>> IMA
>>>>>> namespace.
>>>>>>
>>>>>> Implement ima_free_measurements() to free a list of
>>>>>> measurements
>>>>>> and call it when an IMA namespace is deleted.
>>>>> This one worries me quite a lot.  What seems to be happening in
>>>>> this
>>>>> code:
>>>>>
>>>>>> @@ -107,7 +100,7 @@ static int ima_add_digest_entry(struct
>>>>>> ima_namespace *ns,
>>>>>>            qe->entry = entry;
>>>>>>     
>>>>>>            INIT_LIST_HEAD(&qe->later);
>>>>>> -       list_add_tail_rcu(&qe->later, &ima_measurements);
>>>>>> +       list_add_tail_rcu(&qe->later, &ns->ima_measurements);
>>>>>>     
>>>>>>            atomic_long_inc(&ns->ima_htable.len);
>>>>>>            if (update_htable) {
>>>>>>
>>>>> is that we now only add the measurements to the namespace list,
>>>>> but
>>>>> that list is freed when the namespace dies.  However, the
>>>>> measurement
>>>>> is still extended through the PCRs meaning we have incomplete
>>>>> information for a replay after the namespace dies?
>>>> *Not at all.* The measurement list of the namespace is
>>>> independent
>>>> of
>>>> the host.
>>>>
>>>> The cover letter states:
>>> I get that the host can set up a policy to log everything in the
>>> namespace, but that wasn't my question.  My question is can the
>>> guest
>>> set up a policy to log something that doesn't go into the host log
>>> (because the host hasn't asked for it to be logged) but extends a
>>> PCR
>>> anyway, thus destroying the ability of the host to do log replay.
>> host log goes with host TPM and vice versa
>>
>> guest log goes with (optional) vTPM and vice version
> But that's what doesn't seem to happen ... ima_pcr_extend isn't
> virtualized and it's always called from ima_add_template_entry()
> meaning the physical TPM is always extended even for a namespace only
> entry.

You cannot set a measurement rule in the namespace. That is prevented 
per 9/20: ima: Only accept AUDIT rules for IMA non-init_ima_ns 
namespaces for now.

Also, with the tests that I have done with IMA namespaces I have not 
seen any 'evmctl ima_measurement ...' failures.

Have you been able to cause the IMA namespace to do measurements? It 
would be an easy thing to move the tpm_chip into the ima_namespace as 
well, but per 9/20 this shouldn't be necessary at this point.

>   
>
>> Extending the PCR of the host's TPM would require the data to be
>> logged in the host log as well. So, no, it's not possible.
> Well, exactly: if you don't have or want a vTPM per container the only
> way to attest is via the physical TPM which means all entries in the
> namespace must be in the host log, so the host owner can quote and
> reply and they can split the attested log and give assurance to the
> namespaces that their entries are correct.

Yes, this series allows you to log into the system log and along with 
this extend the TPM PCR.


>
> James
>
>