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 */
> >
> > /*
>
