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

[Mimi Zohar]

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.

> +	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 */
>  
>  /*

-- 
thanks,

Mimi