Re: [PATCH] tpm: efi: Don't create binary_bios_measurements file for an empty log

[Tyler Hicks <tyhicks@linux.microsoft.com>]

On 2020-10-28 11:30:11, Tyler Hicks wrote:
> So, we need help from Kai, Kenneth, or Mimi to verify my assumption that
> their firmware is providing an empty main event log and a populated
> final event log.

Hi Kai, Kenneth, and Mimi - could one or two of you please follow these
steps:

1) Apply the proposed patch in the grandparent of this email so that
   your kernel doesn't crash
2) Revert commit 7f3d176f5f7e ("tpm: Require that all digests are
   present in TCG_PCR_EVENT2 structures") so that
   __calc_tpm2_event_size() goes back to being less picky and may treat
   a final log event as a valid event log header
3) Add some debugging warnings in efi_tpm_eventlog_init() to check for
   an empty main event log and a populated final event log, as shown
   below
4) Boot the resulting kernel build, look for the warnings, and report
   back

diff --git a/drivers/firmware/efi/tpm.c b/drivers/firmware/efi/tpm.c
index c1955d320fec..c4d2dbd5ed42 100644
--- a/drivers/firmware/efi/tpm.c
+++ b/drivers/firmware/efi/tpm.c
@@ -78,6 +78,9 @@ int __init efi_tpm_eventlog_init(void)
 		goto out;
 	}
 
+	WARN(!log_tbl->size && final_tbl->nr_events,
+	     "nr_events = %llu\n", final_tbl->nr_events);
+
 	tbl_size = 0;
 	if (final_tbl->nr_events != 0) {
 		void *events = (void *)efi.tpm_final_log
@@ -95,6 +98,8 @@ int __init efi_tpm_eventlog_init(void)
 		goto out_calc;
 	}
 
+	WARN(!log_tbl->size && tbl_size, "tbl_size = %d\n", tbl_size);
+
 	memblock_reserve((unsigned long)final_tbl,
 			 tbl_size + sizeof(*final_tbl));
 	efi_tpm_final_log_size = tbl_size;

For your convenience, I've created a branch with these changes on top of
v5.9:

 https://git.kernel.org/pub/scm/linux/kernel/git/tyhicks/linux.git/log/?h=tpm/bin-bios-measurements-debug

Thank you!

Tyler