[PATCH v2 7/7] ima: record log size at kexec load and execute

[Stefan Berger]

On 10/5/23 14:26, Tushar Sugandhi wrote:
> The window between kexec 'load' and 'execute' could be arbitrarily long.
> Even with the large chunk of memory allocated at kexec 'load', it may
> run out which would result in missing events in IMA log after the system
> soft reboots to the new Kernel.  This would result in IMA measurements
> getting out of sync with the TPM PCR quotes which would result in remote
> attestation failing for that system.  There is currently no way for the
> new Kernel to know if the IMA log TPM PCR quote out of sync problem is
> because of the missing measurements during kexec.
>
> Define two new IMA events, 'kexec_load' and 'kexec_execute', to be
> measured at kexec 'load' and 'execute' respectively.
>
> IMA measures 'boot_aggregate' as the first event when the system boots -
> either cold boot or kexec soft boot.  In case when the system goes
> through multiple soft reboots, the number of 'boot_aggregate' events in
> IMA log corresponds to total number of boots (cold boot plus multiple
> kexec soft reboots).  With this change, there would be additional
> 'kexec_load' and 'kexec_execute' events in between the two
> 'boot_aggregate' events.  In rare cases, when the system runs out of
> memory during kexec soft reboot, 'kexec_execute' won't be copied since
> its one of the very last event measured just before kexec soft reboot.
> The absence of the event 'kexec_execute' in between the two
> boot_aggregate' events would signal the attestation service that the IMA
> log on the system is out of sync with TPM PCR quotes and the system needs
> to be cold booted for the remote attestation to succeed again.
>
>
> @@ -198,6 +208,7 @@ void ima_add_kexec_buffer(struct kimage *image)
>   static int ima_update_kexec_buffer(struct notifier_block *self,
>   				   unsigned long action, void *data)
>   {
> +	char ima_kexec_event[IMA_KEXEC_EVENT_LEN];
>   	void *buf = NULL;
>   	size_t buf_size;
>   	bool resume = false;
> @@ -213,9 +224,31 @@ static int ima_update_kexec_buffer(struct notifier_block *self,
>   		return NOTIFY_OK;
>   	}
>   
> +	buf_size = ima_get_binary_runtime_size();
> +	scnprintf(ima_kexec_event, IMA_KEXEC_EVENT_LEN,
> +		  "kexec_segment_size=%lu;ima_binary_runtime_size=%lu;",
> +		  kexec_segment_size, buf_size);
> +
> +	/*
> +	 * This is one of the very last events measured by IMA before kexec
> +	 * soft rebooting into the new Kernal.
> +	 * This event can be used as a marker after the system soft reboots
> +	 * to the new Kernel to check if there was sufficient memory allocated
> +	 * at kexec 'load' to capture the events measured between the window
> +	 * of kexec 'load' and 'execute'.
> +	 * This event needs to be present in the IMA log, in between the two
> +	 * 'boot_aggregate' events that are logged for the previous boot and
> +	 * the current soft reboot. If it is not present after the system soft
> +	 * reboots into the new Kernel, it would mean the IMA log is not
> +	 * consistent with the TPM PCR quotes, and the system needs to be
> +	 * cold-booted for the attestation to succeed again.
> +	 */
> +	ima_measure_critical_data("ima_kexec", "kexec_execute",
> +				  ima_kexec_event, strlen(ima_kexec_event),
> +				  false, NULL, 0);
> +
>   	ima_measurements_suspend();
>   
> -	buf_size = ima_get_binary_runtime_size();

This should be removed earlier, in 2/7.



>   	ret = ima_dump_measurement_list(&buf_size, &buf,
>   					kexec_segment_size);
>