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Message-ID: <cdcd63f7-ce1f-4463-f886-c36832d7a706@linux.microsoft.com>
Date: Fri, 6 Nov 2020 07:37:16 -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 7:24 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@...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.
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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