[PATCH 06/10] ima: update buffer at kexec execute with ima measurements

[Tushar Sugandhi]

Adding Eric to cc.

On 7/7/23 12:49, Mimi Zohar wrote:
> On Fri, 2023-07-07 at 11:01 -0400, Mimi Zohar wrote:
>> Hi Tushar,
>>
>> On Mon, 2023-07-03 at 14:57 -0700, Tushar Sugandhi wrote:
>>
>>> +/*
>>> + * Called during kexec execute so that IMA can update the measurement list.
>>> + */
>>> +static int ima_update_kexec_buffer(struct notifier_block *self,
>>> +				   unsigned long action, void *data)
>>> +{
>>> +	void *new_buffer = NULL;
>>> +	size_t new_buffer_size, cur_buffer_size;
>>> +	bool resume = false;
>>> +
>>> +	if (!kexec_in_progress) {
>>> +		pr_info("%s: No kexec in progress.\n", __func__);
>>> +		return NOTIFY_OK;
>>> +	}
>>> +
>>> +	if (!ima_kexec_buffer) {
>>> +		pr_err("%s: Kexec buffer not set.\n", __func__);
>>> +		return NOTIFY_OK;
>>> +	}
>>> +
>>> +	ima_measurements_suspend();
>>> +
>>> +	cur_buffer_size = kexec_segment_size - sizeof(struct ima_kexec_hdr);
>>> +	new_buffer_size = ima_get_binary_runtime_size();
>>> +	if (new_buffer_size > cur_buffer_size) {
>>> +		pr_err("%s: Measurement list grew too large.\n", __func__);
>>> +		resume = true;
>>> +		goto out;
>>> +	}
>> This changes the current behavior of carrying as many measurements
>> across kexec as possible.  True the measurement list won't verify
>> against the TPM PCRs, but not copying the measurements leaves the
>> impression there weren't any previous measurements.
>>
>> This also explains the reason for allocating an IMA buffer (patch 1/10)
>> and not writing the measurements directly into the kexec buffer.
> If not carrying even a partial measurement list across kexec is
> desired, then in addition to the "boot_aggregate" record, define a new
> record containing the TPM pcrcounter.  With this information,
> attestation servers will at least be able to detect if the measurement
> list was truncated.
>
> thanks,
>
> Mimi
Sure.  Recording TPM pcrcounter at boot aggregate and
Kexec 'load' should provide the necessary information to the
attestation servers.  We can implement this if needed, based on how
rest of the series evolves.

~Tushar
>>> +	ima_populate_buf_at_kexec_execute(&new_buffer_size, &new_buffer);
>>> +
>>> +	if (!new_buffer) {
>>> +		pr_err("%s: Dump measurements failed.\n", __func__);
>>> +		resume = true;
>>> +		goto out;
>>> +	}
>>> +	memcpy(ima_kexec_buffer, new_buffer, new_buffer_size);
>>> +out:
>>> +	kimage_unmap_segment(ima_kexec_buffer);
>>> +	ima_kexec_buffer = NULL;
>>> +
>>> +	if (resume)
>>> +		ima_measurements_resume();
>>> +
>>> +	return NOTIFY_OK;
>>> +}
>>> +
>>>   #endif /* IMA_KEXEC */
>>>   
>>>   /*