Re: [PATCH v5 6/7] IMA: add critical_data to the built-in policy rules

[Lakshmi Ramasubramanian <nramas@linux.microsoft.com>]

On 11/6/20 7:24 AM, Mimi Zohar wrote:

Hi Mimi,

Thanks for reviewing the patches.

> 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@linux.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@linux.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.

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();
>>   }
>>   
>