[PATCH] tpm: measure DTB in PCR1 instead of PCR0

Ilias Apalodimas ilias.apalodimas at linaro.org
Fri Jun 14 14:09:50 CEST 2024


The PC client spec [0], doesn't describe measurements for DTBs. It does
describe what do to for ACPI tables though.

There is a description for ACPI in 3.3.4.1 PCR[0] – SRTM, POST BIOS,
and Embedded Drivers and they explicitly mention ACPI in there. There's
no mention of ACPI in 3.3.4.2 PCR[1] – Host Platform Configuration.

However, in Figure 6 --  PCR Mapping of UEFI Components ACPI is shown
in PCR1. The general description also mentions PCR0 is for code and PCR1
is for data such as ACPI and SMBIOS.

So let's switch over the DTB measurements to PCR1 which seems a better
fit.

[0] https://trustedcomputinggroup.org/resource/pc-client-specific-platform-firmware-profile-specification

Reported-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
---
 boot/bootm.c              | 2 +-
 lib/efi_loader/efi_tcg2.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/boot/bootm.c b/boot/bootm.c
index 6fa8edab021e..3de87eb185d7 100644
--- a/boot/bootm.c
+++ b/boot/bootm.c
@@ -963,7 +963,7 @@ int bootm_measure(struct bootm_headers *images)
 			goto unmap_initrd;

 		if (IS_ENABLED(CONFIG_MEASURE_DEVICETREE)) {
-			ret = tcg2_measure_data(dev, &elog, 0, images->ft_len,
+			ret = tcg2_measure_data(dev, &elog, 1, images->ft_len,
 						(u8 *)images->ft_addr,
 						EV_TABLE_OF_DEVICES,
 						strlen("dts") + 1,
diff --git a/lib/efi_loader/efi_tcg2.c b/lib/efi_loader/efi_tcg2.c
index 51264c1b998c..a8a54c9f131d 100644
--- a/lib/efi_loader/efi_tcg2.c
+++ b/lib/efi_loader/efi_tcg2.c
@@ -1328,7 +1328,7 @@ efi_status_t efi_tcg2_measure_dtb(void *dtb)
 	sha256_update(&hash_ctx, (u8 *)dtb + fdt_off_mem_rsvmap(dtb), rsvmap_size);
 	sha256_finish(&hash_ctx, blob->data + blob->blob_description_size);

-	ret = measure_event(dev, 0, EV_POST_CODE, event_size, (u8 *)blob);
+	ret = measure_event(dev, 1, EV_POST_CODE, event_size, (u8 *)blob);

 	free(blob);
 	return ret;
--
2.45.1



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