[PATCH 5.3 064/112] efi/tpm: Dont traverse an event log with no events

[Greg Kroah-Hartman]

From: Peter Jones <pjones@xxxxxxxxxx>

commit 05c8c1ff81ed2eb9bad7c27cf92e55c864c16df8 upstream.

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.

Tested-by: Lyude Paul <lyude@xxxxxxxxxx>
Signed-off-by: Peter Jones <pjones@xxxxxxxxxx>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
Acked-by: Matthew Garrett <mjg59@xxxxxxxxxx>
Acked-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Cc: Ben Dooks <ben.dooks@xxxxxxxxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: Jerry Snitselaar <jsnitsel@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Lukas Wunner <lukas@xxxxxxxxx>
Cc: Octavian Purdila <octavian.purdila@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Scott Talbert <swt@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-efi@xxxxxxxxxxxxxxx
Cc: linux-integrity@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Fixes: c46f3405692d ("tpm: Reserve the TPM final events table")
Link: https://lkml.kernel.org/r/20191002165904.8819-5-ard.biesheuvel@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/firmware/efi/tpm.c |   15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

--- a/drivers/firmware/efi/tpm.c
+++ b/drivers/firmware/efi/tpm.c
@@ -75,11 +75,16 @@ 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));