Re: [PATCH v6 7/8] IMA: add a built-in policy rule for critical data measurement

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

On 11/20/20 6:30 AM, Mimi Zohar wrote:

Hi Mimi,

> 
> On Thu, 2020-11-19 at 15:26 -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.
>> Define a new critical data builtin policy to allow measuring
>> early kernel integrity critical data before a custom IMA policy is
>> loaded.
> 
> Everything needing to be said seems to be included in the second
> sentence.  Does the first sentence add anything?  "Define a new
> critical data builtin policy" makes for a good Subject line.

Agreed - will update.

> 
>>
>> Add critical data to built-in IMA rules if the kernel command line
>> contains "ima_policy=critical_data".
> 
> The boot command line parameters are defined in Documentation/admin-
> guide/kernel-parameters.txt.  Please update "ima_policy".

Will do.

> 
>>
>> Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
>> ---
>>   security/integrity/ima/ima_policy.c | 12 ++++++++++++
>>   1 file changed, 12 insertions(+)
>>
>> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
>> index c9e52dab0638..119604a3efa0 100644
>> --- a/security/integrity/ima/ima_policy.c
>> +++ b/security/integrity/ima/ima_policy.c
>> @@ -206,6 +206,10 @@ static struct ima_rule_entry secure_boot_rules[] __ro_after_init = {
>>   	 .flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
>>   };
>>
>> +static struct ima_rule_entry critical_data_rules[] __ro_after_init = {
>> +	{.action = MEASURE, .func = CRITICAL_DATA, .flags = IMA_FUNC},
>> +};
>> +
>>   /* An array of architecture specific rules */
>>   static struct ima_rule_entry *arch_policy_entry __ro_after_init;
>>   
>> @@ -228,6 +232,7 @@ __setup("ima_tcb", default_measure_policy_setup);
>>   
>>   static bool ima_use_appraise_tcb __initdata;
>>   static bool ima_use_secure_boot __initdata;
>> +static bool ima_use_critical_data __ro_after_init;
> 
> Unlike ima_fail_unverifiable_sigs, ima_use_critical_data is only used
> during __init.  Please change "__ro_after_init" to "__initdata".  (The
> critical data policy itself is defined properly as __ro_after_init.)

Will do.

> 
>>   static bool ima_fail_unverifiable_sigs __ro_after_init;
>>   static int __init policy_setup(char *str)
>>   {
>> @@ -242,6 +247,8 @@ static int __init policy_setup(char *str)
>>   			ima_use_appraise_tcb = true;
>>   		else if (strcmp(p, "secure_boot") == 0)
>>   			ima_use_secure_boot = true;
>> +		else if (strcmp(p, "critical_data") == 0)
>> +			ima_use_critical_data = true;
>>   		else if (strcmp(p, "fail_securely") == 0)
>>   			ima_fail_unverifiable_sigs = true;
>>   		else
>> @@ -875,6 +882,11 @@ void __init ima_init_policy(void)
>>   			  ARRAY_SIZE(default_appraise_rules),
>>   			  IMA_DEFAULT_POLICY);
>>   
>> +	if (ima_use_critical_data)
>> +		add_rules(critical_data_rules,
>> +			  ARRAY_SIZE(critical_data_rules),
>> +			  IMA_DEFAULT_POLICY);
>> +
>>   	ima_update_policy_flag();
>>   }
>>   
> 

thanks,
  -lakshmi