tpm: Don't duplicate events from the final event log in the TCG2 log

After the first call to GetEventLog() on UEFI systems using the TCG2
crypto agile log format, any further log events (other than those
triggered by ExitBootServices()) will be logged in both the main log and
also in the Final Events Log. While the kernel only calls GetEventLog()
immediately before ExitBootServices(), we can't control whether earlier
parts of the boot process have done so. This will result in log entries
that exist in both logs, and so the current approach of simply appending
the Final Event Log to the main log will result in events being
duplicated.

We can avoid this problem by looking at the size of the Final Event Log
just before we call ExitBootServices() and exporting this to the main
kernel. The kernel can then skip over all events that occured before
ExitBootServices() and only append events that were not also logged to
the main log.

Signed-off-by: Matthew Garrett <mjg59@google.com>
Reported-by: Joe Richey <joerichey@google.com>
Suggested-by: Joe Richey <joerichey@google.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/drivers/char/tpm/eventlog/efi.c b/drivers/char/tpm/eventlog/efi.c
index 73b981026627..6bb023de17f1 100644
--- a/drivers/char/tpm/eventlog/efi.c
+++ b/drivers/char/tpm/eventlog/efi.c
@@ -75,6 +75,8 @@ int tpm_read_log_efi(struct tpm_chip *chip)
 		goto out;
 	}
 
+	efi_tpm_final_log_size -= log_tbl->final_events_preboot_size;
+
 	tmp = krealloc(log->bios_event_log,
 		       log_size + efi_tpm_final_log_size,
 		       GFP_KERNEL);
@@ -85,8 +87,15 @@ int tpm_read_log_efi(struct tpm_chip *chip)
 	}
 
 	log->bios_event_log = tmp;
+
+	/*
+	 * Copy any of the final events log that didn't also end up in the
+	 * main log. Events can be logged in both if events are generated
+	 * between GetEventLog() and ExitBootServices().
+	 */
 	memcpy((void *)log->bios_event_log + log_size,
-	       final_tbl->events, efi_tpm_final_log_size);
+	       final_tbl->events + log_tbl->final_events_preboot_size,
+	       efi_tpm_final_log_size);
 	log->bios_event_log_end = log->bios_event_log +
 		log_size + efi_tpm_final_log_size;