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Message-ID: <d92869b5-7244-e29e-5d30-c0e06cf45be1@linux.microsoft.com>
Date: Fri, 6 Nov 2020 15:51:51 -0800
From: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To: Mimi Zohar <zohar@...ux.ibm.com>,
Tushar Sugandhi <tusharsu@...ux.microsoft.com>,
stephen.smalley.work@...il.com, casey@...aufler-ca.com,
agk@...hat.com, snitzer@...hat.com, gmazyland@...il.com,
paul@...l-moore.com
Cc: tyhicks@...ux.microsoft.com, sashal@...nel.org, jmorris@...ei.org,
linux-integrity@...r.kernel.org, selinux@...r.kernel.org,
linux-security-module@...r.kernel.org,
linux-kernel@...r.kernel.org, dm-devel@...hat.com
Subject: Re: [PATCH v5 6/7] IMA: add critical_data to the built-in policy
rules
On 11/6/20 7:37 AM, Lakshmi Ramasubramanian wrote:
Hi Mimi,
>
>> Hi Lakshmi, Tushar,
>>
>> This patch defines a new critical_data builtin policy. Please update
>> the Subject line.
>>
>> On Sun, 2020-11-01 at 14:26 -0800, Tushar Sugandhi wrote:
>>> From: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
>>>
>>> The IMA hook to measure kernel critical data, namely
>>> ima_measure_critical_data(), could be called before a custom IMA policy
>>> is loaded. For example, SELinux calls ima_measure_critical_data() to
>>> measure its state and policy when they are initialized. This occurs
>>> before a custom IMA policy is loaded, and hence IMA hook will not
>>> measure the data. A built-in policy is therefore needed to measure
>>> critical data provided by callers before a custom IMA policy is loaded.
>>
>> ^Define a new critical data builtin policy to allow measuring early
>> kernel integrity critical data before a custom IMA policy is loaded.
>
> I will add the above line in the patch description.
>
>>
>> Either remove the references to SELinux or move this patch after the
>> subsequent patch which measures SELinux critical data.
>
> I will remove the reference to SELinux.
> I think it would be better to have this patch before the SELinux
> measurement patch.
>
>>
>>>
>>> Add CRITICAL_DATA to built-in IMA rules if the kernel command line
>>> contains "ima_policy=critical_data". Set the IMA template for this rule
>>> to "ima-buf" since ima_measure_critical_data() measures a buffer.
>>>
>>> Signed-off-by: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
>>
>>> ---
>>> security/integrity/ima/ima_policy.c | 32 +++++++++++++++++++++++++++++
>>> 1 file changed, 32 insertions(+)
>>>
>>> diff --git a/security/integrity/ima/ima_policy.c
>>> b/security/integrity/ima/ima_policy.c
>>> index ec99e0bb6c6f..dc8fe969d3fe 100644
>>> --- a/security/integrity/ima/ima_policy.c
>>> +++ b/security/integrity/ima/ima_policy.c
>>
>>> @@ -875,6 +884,29 @@ void __init ima_init_policy(void)
>>> ARRAY_SIZE(default_appraise_rules),
>>> IMA_DEFAULT_POLICY);
>>> + if (ima_use_critical_data) {
>>> + template = lookup_template_desc("ima-buf");
>>> + if (!template) {
>>> + ret = -EINVAL;
>>> + goto out;
>>> + }
>>> +
>>> + ret = template_desc_init_fields(template->fmt,
>>> + &(template->fields),
>>> + &(template->num_fields));
>>
>> The default IMA template when measuring buffer data is "ima_buf". Is
>> there a reason for allocating and initializing it here and not
>> deferring it until process_buffer_measurement()?
>>
>
> You are right - good catch.
> I will remove the above and validate.
>
process_buffer_measurement() allocates and initializes "ima-buf"
template only when the parameter "func" is NONE. Currently, only
ima_check_blacklist() passes NONE for func when calling
process_buffer_measurement().
If "func" is anything other than NONE, ima_match_policy() picks
the default IMA template if the IMA policy rule does not specify a template.
We need to add "ima-buf" in the built-in policy for critical_data so
that the default template is not used for buffer measurement.
Please let me know if I am missing something.
thanks,
-lakshmi
>>
>>> + if (ret)
>>> + goto out;
>>> +
>>> + critical_data_rules[0].template = template;
>>> + add_rules(critical_data_rules,
>>> + ARRAY_SIZE(critical_data_rules),
>>> + IMA_DEFAULT_POLICY);
>>> + }
>>> +
>>> +out:
>>> + if (ret)
>>> + pr_err("%s failed, result: %d\n", __func__, ret);
>>> +
>>> ima_update_policy_flag();
>>> }
>>
>
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