[PATCH 2/2] efi+tpm: don't traverse an event log with no events

[Peter Jones]

When there are no entries to put into the final event log, some machines
will return the template they would have populated anyway.  In this case
the nr_events field is 0, but the rest of the log is just garbage.

This patch stops us from trying to iterate the table with
__calc_tpm2_event_size() when the number of events in the table is 0.

Signed-off-by: Peter Jones <pjones@xxxxxxxxxx>
Tested-by: Lyude Paul <lyude@xxxxxxxxxx>
---
 drivers/firmware/efi/tpm.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/firmware/efi/tpm.c b/drivers/firmware/efi/tpm.c
index 1d3f5ca3eaa..be51ed17c6e 100644
--- a/drivers/firmware/efi/tpm.c
+++ b/drivers/firmware/efi/tpm.c
@@ -75,11 +75,15 @@ int __init efi_tpm_eventlog_init(void)
 		goto out;
 	}
 
-	tbl_size = tpm2_calc_event_log_size((void *)efi.tpm_final_log
-					    + sizeof(final_tbl->version)
-					    + sizeof(final_tbl->nr_events),
-					    final_tbl->nr_events,
-					    log_tbl->log);
+	tbl_size = 0;
+	if (final_tbl->nr_events != 0) {
+		void *events = (void *)efi.tpm_final_log
+				+ sizeof(final_tbl->version)
+				+ sizeof(final_tbl->nr_events);
+		tbl_size = tpm2_calc_event_log_size(events,
+						    final_tbl->nr_events,
+						    log_tbl->log);
+	}
 	memblock_reserve((unsigned long)final_tbl,
 			 tbl_size + sizeof(*final_tbl));
 	early_memunmap(final_tbl, sizeof(*final_tbl));
-- 
2.23.0.rc2