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

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Date:   Mon, 26 Aug 2019 11:30:28 -0400
From:   Peter Jones <pjones@...hat.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Roberto Sassu <roberto.sassu@...wei.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Bartosz Szczepanek <bsz@...ihalf.com>,
        Lyude Paul <lyude@...hat.com>, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, Peter Jones <pjones@...hat.com>
Subject: [PATCH 2/2] efi+tpm: don't traverse an event log with no events

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@...hat.com>
Tested-by: Lyude Paul <lyude@...hat.com>
---
 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