security/vboot: Add rollback NVRAM space for TPM 2

Create an NVRAM space in TPM 2.0 that survives owner clear and can be
read and written without authorization. This space allows to seal data
with the TPM that can only be unsealed before the space was cleared.
It will be used during ChromeOS enterprise rollback to securely
carry data across a TPM clear.

Public documentation on the rollback feature:
https://source.chromium.org/chromium/chromiumos/platform2/+/main:oobe_config/README.md

BUG=b/233746744

Signed-off-by: Miriam Polzer <mpolzer@google.com>
Change-Id: I59ca0783b41a6f9ecd5b72f07de6fb403baf2820
Reviewed-on: https://review.coreboot.org/c/coreboot/+/66623
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

2 files changed, 36 insertions, 0 deletions

diff --git a/src/security/vboot/antirollback.h b/src/security/vboot/antirollback.h
index 75bfcdc7c772..10a9e21e378b 100644
--- a/src/security/vboot/antirollback.h
+++ b/src/security/vboot/antirollback.h
@@ -28,6 +28,7 @@ enum vb2_pcr_digest;
 /* 0x100d: Hash of MRC_CACHE training data for non-recovery boot */
 #define MRC_RW_HASH_NV_INDEX            0x100d
 #define HASH_NV_SIZE                    VB2_SHA256_DIGEST_SIZE
+#define ENT_ROLLBACK_SPACE_INDEX        0x100e
 /* Widevine Secure Counter space */
 #define WIDEVINE_COUNTER_NV_INDEX(n)	(0x3000 + (n))
 #define NUM_WIDEVINE_COUNTERS		4
diff --git a/src/security/vboot/secdata_tpm.c b/src/security/vboot/secdata_tpm.c
index 3ad7fc8a7524..78850696c4fa 100644
--- a/src/security/vboot/secdata_tpm.c
+++ b/src/security/vboot/secdata_tpm.c
@@ -116,6 +116,17 @@ static const TPMA_NV rw_space_attributes = {
 	.TPMA_NV_WRITE_STCLEAR = 1,
 };
 
+static const TPMA_NV rw_auth_space_attributes = {
+	.TPMA_NV_AUTHWRITE = 1,
+	.TPMA_NV_AUTHREAD = 1,
+	.TPMA_NV_NO_DA = 1,
+	.TPMA_NV_PPREAD = 1,
+	.TPMA_NV_PPWRITE = 1,
+	.TPMA_NV_PLATFORMCREATE = 1,
+	.TPMA_NV_WRITE_STCLEAR = 1,
+	.TPMA_NV_POLICY_DELETE = 1,
+};
+
 static const TPMA_NV fwmp_attr = {
 	.TPMA_NV_PLATFORMCREATE = 1,
 	.TPMA_NV_OWNERWRITE = 1,
@@ -342,6 +353,22 @@ static uint32_t setup_zte_spaces(void)
 	return rv;
 }
 
+/*
+ * Set up enterprise rollback space.
+ *
+ * This space is not used by firmware but needs to survive owner clear. Thus, it
+ * needs to be created here.
+ */
+static uint32_t enterprise_rollback_create_space(void)
+{
+	uint8_t rollback_space_default[32] = {0};
+
+	return setup_space("Enterprise Rollback Space",
+			   ENT_ROLLBACK_SPACE_INDEX, rollback_space_default,
+			   sizeof(rollback_space_default), rw_auth_space_attributes,
+			   unsatisfiable_policy, sizeof(unsatisfiable_policy));
+}
+
 static uint32_t setup_widevine_counter_spaces(void)
 {
 	uint32_t index, rv;
@@ -387,6 +414,14 @@ static uint32_t _factory_initialize_tpm(struct vb2_context *ctx)
 	if (CONFIG(CHROMEOS) && !(CONFIG(TPM_GOOGLE)))
 		RETURN_ON_FAILURE(setup_zte_spaces());
 
+	/*
+	 * On TPM 2.0, create a space that survives TPM clear. This allows to
+	 * securely lock data during enterprise rollback by binding to this
+	 * space's value.
+	 */
+	if (CONFIG(CHROMEOS))
+		RETURN_ON_FAILURE(enterprise_rollback_create_space());
+
 	/* Define widevine counter space. No need to increment/write to the secure counters
 	   and are expected to be incremented during the first use. */
 	if (CONFIG(VBOOT_DEFINE_WIDEVINE_COUNTERS))