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Subject[PATCH 4/7] efi/tpm: don't traverse an event log with no events
Date
From: Peter Jones <pjones@redhat.com>

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.

Fixes: c46f3405692d ("tpm: Reserve the TPM final events table")
Cc: linux-efi@vger.kernel.org
Cc: linux-integrity@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Peter Jones <pjones@redhat.com>
Tested-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Acked-by: Matthew Garrett <mjg59@google.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
drivers/firmware/efi/tpm.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/firmware/efi/tpm.c b/drivers/firmware/efi/tpm.c
index 1d3f5ca3eaaf..b9ae5c6f9b9c 100644
--- 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));
--
2.20.1
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