commit 1fbc1123d798137324cc8876db6386584c475da1
author Matt DeVillier <matt.devillier@amd.corp-partner.google.com> Mon Jan 23 18:38:45 2023 -0600
committer Felix Held <felix-coreboot@felixheld.de> Mon Feb 13 14:56:48 2023 +0000
tree d01ab54ffed0756d3610e82d741ad876c567bce4
parent 9ce755d05ed56753105bce6f4d75f4ddbc98cb26

soc/amd/common/block/gfx: Use TPM-stored hash for vbios cache validation

Write the SHA256 hash of the cached VBIOS data when saving to FMAP,
and use it to validate the data read from FMAP on subsequent boots.

Add TPM2 as a dependency to the selection of VBIOS_CACHE_IN_FMAP.

BUG=b:255812886
TEST=tested with rest of patch train

Change-Id: I9c8f23b000b90a1072aeb7a57d3b7b2b2bc626dc
Signed-off-by: Matt DeVillier <matt.devillier@amd.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/72402
Reviewed-by: Martin L Roth <gaumless@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/amd/common/block/graphics/Kconfig

diff --git a/src/soc/amd/common/block/graphics/Kconfig b/src/soc/amd/common/block/graphics/Kconfig
index 511f304..75b4013 100644
--- a/src/soc/amd/common/block/graphics/Kconfig
+++ b/src/soc/amd/common/block/graphics/Kconfig
@@ -13,7 +13,7 @@
 
 config SOC_AMD_GFX_CACHE_VBIOS_IN_FMAP
 	bool "Support for caching modified VBIOS tables in flash"
-	depends on SOC_AMD_COMMON_BLOCK_GRAPHICS && CHROMEOS && RUN_FSP_GOP
+	depends on SOC_AMD_COMMON_BLOCK_GRAPHICS && CHROMEOS && RUN_FSP_GOP && TPM2
 	default n
 	help
 	  Enable support for flash based VBIOS cache.

src/soc/amd/common/block/graphics/graphics.c

diff --git a/src/soc/amd/common/block/graphics/graphics.c b/src/soc/amd/common/block/graphics/graphics.c
index 843bf78..70e3758 100644
--- a/src/soc/amd/common/block/graphics/graphics.c
+++ b/src/soc/amd/common/block/graphics/graphics.c
@@ -9,6 +9,7 @@
 #include <device/pci.h>
 #include <fmap.h>
 #include <fsp/graphics.h>
+#include <security/vboot/vbios_cache_hash_tpm.h>
 #include <security/vboot/vboot_common.h>
 #include <soc/intel/common/vbt.h>
 #include <timestamp.h>
@@ -234,6 +235,9 @@
 						VBIOS_CACHE_FMAP_SIZE) != VBIOS_CACHE_FMAP_SIZE)
 		printk(BIOS_ERR, "Failed to save vbios data to flash; rdev_writeat() failed.\n");
 
+	/* save data hash to TPM NVRAM for validation on subsequent boots */
+	vbios_cache_update_hash(vbios_data, VBIOS_CACHE_FMAP_SIZE);
+
 	printk(BIOS_SPEW, "VBIOS cache successfully written to FMAP.\n");
 }
 
@@ -254,14 +258,11 @@
 /*
  * Return true if VBIOS cache data is valid
  *
- * For now, just compare first 2 bytes of data
- * TODO: replace with TPM hash verification once implemented
+ * Compare hash of data with hash stored in TPM NVRAM
  */
 bool vbios_cache_is_valid(void)
 {
-	bool is_valid = vbios_data[0] == 0x55 && vbios_data[1] == 0xaa;
-	printk(BIOS_SPEW, "VBIOS cache is %s\n", is_valid ? "valid" : "invalid");
-	return is_valid;
+	return vbios_cache_verify_hash(vbios_data, VBIOS_CACHE_FMAP_SIZE) == CB_SUCCESS;
 }
 
 BOOT_STATE_INIT_ENTRY(BS_PRE_DEVICE, BS_ON_EXIT, read_vbios_cache_from_fmap, NULL);