Re: [PATCH] tpm: Don't duplicate events from the final event log in the TCG2 log

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Tue, Jun 04, 2019 at 12:35:11PM -0700, Matthew Garrett wrote:
> After the first call to GetEventLog() on UEFI systems using the TCG2
> crypto agile log format, any further log events (other than those
> triggered by ExitBootServices()) will be logged in both the main log and
> also in the Final Events Log. While the kernel only calls GetEventLog()
> immediately before ExitBootServices(), we can't control whether earlier
> parts of the boot process have done so. This will result in log entries
> that exist in both logs, and so the current approach of simply appending
> the Final Event Log to the main log will result in events being
> duplicated.

Sounds flakky how UEFI firmaware works. Wonder why the ignition of the
final events log is bound to the invokation of GetEventLog() in the
first place.

> We can avoid this problem by looking at the size of the Final Event Log
> just before we call ExitBootServices() and exporting this to the main
> kernel. The kernel can then skip over all events that occured before
> ExitBootServices() and only append events that were not also logged to
> the main log.
> 
> Signed-off-by: Matthew Garrett <mjg59@google.com>
> Reported-by: Joe Richey <joerichey@google.com>
> Suggested-by: Joe Richey <joerichey@google.com>

Rename final_events_early_size as final_events_preboot_size because it
is a bit more descriptive name. Other than that looks good to me.

/Jarkko