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

[Mimi Zohar <zohar@linux.ibm.com>]

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

> 
> > +	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 */
> >  
> >  /*
> 



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