libstub,tpm: do not ignore failure case when reading final event log

JIRA: https://issues.redhat.com/browse/RHEL-72764

Upstream Status: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

commit 63971b0
Author: Gregory Price <gourry@gourry.net>
Date:   Fri Sep 13 19:19:54 2024 -0400

    libstub,tpm: do not ignore failure case when reading final event log

    Current code fails to check for an error case when reading events
    from final event log to calculate offsets.  Check the error case,
    and break early because all subsequent calls will also fail.

    Signed-off-by: Gregory Price <gourry@gourry.net>
    Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Signed-off-by: Štěpán Horáček <shoracek@redhat.com>

Author: shoracek

drivers/firmware/efi/libstub/tpm.c

@@ -124,6 +124,9 @@ static void efi_retrieve_tcg2_eventlog(int version, efi_physical_addr_t log_loca
 			event_size = __calc_tpm2_event_size(header,
 						   (void *)(long)log_location,
 						   false);
+			/* If calc fails this is a malformed log */
+			if (!event_size)
+				break;
 			final_events_size += event_size;
 			i--;
 		}