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.

Tested-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Acked-by: Matthew Garrett <mjg59@google.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Ben Dooks <ben.dooks@codethink.co.uk>
Cc: Dave Young <dyoung@redhat.com>
Cc: Jerry Snitselaar <jsnitsel@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Lukas Wunner <lukas@wunner.de>
Cc: Octavian Purdila <octavian.purdila@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Talbert <swt@techie.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Cc: linux-integrity@vger.kernel.org
Cc: stable@vger.kernel.org
Fixes: c46f3405692d ("tpm: Reserve the TPM final events table")
Link: https://lkml.kernel.org/r/20191002165904.8819-5-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/drivers/firmware/efi/tpm.c b/drivers/firmware/efi/tpm.c
index 1d3f5ca3eaaf8b6397b39e17a8676be3466f2e26..b9ae5c6f9b9c4cd5afee425fa2e78dfeb71a1718 100644 (file)
--- 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));