Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Peter Jones <pjones@redhat.com>
To:     Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        Roberto Sassu <roberto.sassu@huawei.com>,
        Matthew Garrett <mjg59@google.com>,
        Bartosz Szczepanek <bsz@semihalf.com>,
        Lyude Paul <lyude@redhat.com>, linux-efi@vger.kernel.org,
        linux-kernel@vger.kernel.org, Peter Jones <pjones@redhat.com>
Subject: [PATCH 2/2] efi+tpm: don't traverse an event log with no events
Date:   Mon, 26 Aug 2019 11:30:28 -0400
Message-Id: <20190826153028.32639-2-pjones@redhat.com>
In-Reply-To: <20190826153028.32639-1-pjones@redhat.com>
References: <20190826153028.32639-1-pjones@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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