rats-tls: csv: validate the hmac of PEK and ChipId in attester

Signed-off-by: hanliyang <[email protected]>

src/attesters/csv/collect_evidence.c

@@ -282,6 +282,32 @@ static int collect_attestation_evidence(uint8_t *hash, uint32_t hash_len,
 
 	/* Fill evidence buffer with attestation report */
 	assert(sizeof(csv_attestation_report) <= CSV_GUEST_MAP_LEN);
+
+	/* The PEK and ChipId are stored in csv_attestation_report, it's necessary
+	 * to validate PEK and ChipId before transfer to verifier.
+	 */
+	hash_block_t hmac;
+
+	memset((void *)&hmac, 0, sizeof(hash_block_t));
+	ret = sm3_hmac((const char *)report_mnonce, CSV_ATTESTATION_MNONCE_SIZE,
+		       (const unsigned char *)attestation_report +
+			       CSV_ATTESTATION_REPORT_HMAC_DATA_OFFSET,
+		       CSV_ATTESTATION_REPORT_HMAC_DATA_SIZE, (unsigned char *)&hmac,
+		       sizeof(hash_block_t));
+	if (ret) {
+		RTLS_ERR("failed to compute sm3 hmac\n");
+		goto err_munmap;
+	}
+	ret = memcmp(&hmac, &attestation_report->hmac, sizeof(hash_block_t));
+	if (ret) {
+		RTLS_ERR("PEK and ChipId may have been tampered with\n");
+		goto err_munmap;
+	}
+	RTLS_DEBUG("check PEK and ChipId successfully\n");
+
+	/* Reserved1 field should be filled with 0 */
+	memset(attestation_report->reserved1, 0, sizeof(attestation_report->reserved1));
+
 	memcpy(evidence->report, (void *)user_data, sizeof(csv_attestation_report));
 
 	/* Fill in CEK cert and HSK cert */

src/attesters/csv/csv_utils.c

@@ -7,6 +7,7 @@
 #include <stddef.h>
 #include <rats-tls/log.h>
 #include <openssl/evp.h>
+#include <openssl/hmac.h>
 
 void gen_random_bytes(void *buf, size_t len)
 {
@@ -46,3 +47,34 @@ int sm3_hash(const unsigned char *data, size_t len, unsigned char *hash, size_t
 
 	return ret;
 }
+
+int sm3_hmac(const char *key, size_t key_len, const unsigned char *data, size_t data_len,
+	     unsigned char *hmac, size_t expected_hmac_len)
+{
+	HMAC_CTX *hmac_ctx = HMAC_CTX_new();
+	const EVP_MD *evp_md = EVP_sm3();
+	int sm3_hmac_out_size = 0;
+	int ret = -1;
+
+	if (hmac_ctx == NULL)
+		return ret;
+
+	if (!HMAC_Init_ex(hmac_ctx, key, key_len, evp_md, NULL))
+		goto err_free_hmac_ctx;
+
+	if (!HMAC_Update(hmac_ctx, data, data_len))
+		goto err_free_hmac_ctx;
+
+	if (!HMAC_Final(hmac_ctx, hmac, &sm3_hmac_out_size))
+		goto err_free_hmac_ctx;
+
+	if (sm3_hmac_out_size != expected_hmac_len)
+		goto err_free_hmac_ctx;
+
+	ret = 0;
+
+err_free_hmac_ctx:
+	HMAC_CTX_free(hmac_ctx);
+
+	return ret;
+}

src/attesters/csv/csv_utils.h

@@ -8,3 +8,5 @@
 
 void gen_random_bytes(void *buf, size_t len);
 int sm3_hash(const unsigned char *data, size_t len, unsigned char *hash, size_t expected_hash_len);
+int sm3_hmac(const char *key, size_t key_len, const unsigned char *data, size_t data_len,
+	     unsigned char *hmac, size_t expected_hmac_len);

src/verifiers/csv/CMakeLists.txt

@@ -16,7 +16,6 @@ link_directories(${LIBRARY_DIRS})
 
 # Set source file
 set(SOURCES cleanup.c
-            csv_utils.c
             hygoncert.c
             init.c
             main.c

src/verifiers/csv/verify_evidence.c

@@ -10,7 +10,6 @@
 #include <rats-tls/verifier.h>
 #include <rats-tls/csv.h>
 #include "hygoncert.h"
-#include "csv_utils.h"
 
 static enclave_verifier_err_t verify_cert_chain(csv_evidence *evidence)
 {
@@ -24,35 +23,9 @@ static enclave_verifier_err_t verify_cert_chain(csv_evidence *evidence)
 	assert(sizeof(hygon_root_cert_t) == HYGON_CERT_SIZE);
 	assert(sizeof(csv_cert_t) == HYGON_CSV_CERT_SIZE);
 
-	/* The PEK and ChipId are stored in csv_attestation_report, it's necessary
-	 * to check whether PEK and ChipId have been tampered with.
-	 */
-	hash_block_t hmac;
-	uint8_t mnonce[CSV_ATTESTATION_MNONCE_SIZE] = {
-		0,
-	};
+	/* Retrieve PEK cert and ChipId */
 	int i, j;
 
-	/* Retrieve mnonce which is the key of sm3-hmac */
-	j = CSV_ATTESTATION_MNONCE_SIZE / sizeof(uint32_t);
-	for (i = 0; i < j; i++)
-		((uint32_t *)mnonce)[i] = ((uint32_t *)report->mnonce)[i] ^ report->anonce;
-
-	memset((void *)&hmac, 0, sizeof(hash_block_t));
-	if (sm3_hmac((const char *)mnonce, CSV_ATTESTATION_MNONCE_SIZE,
-		     (const unsigned char *)report + CSV_ATTESTATION_REPORT_HMAC_DATA_OFFSET,
-		     CSV_ATTESTATION_REPORT_HMAC_DATA_SIZE, (unsigned char *)&hmac,
-		     sizeof(hash_block_t))) {
-		RTLS_ERR("failed to compute sm3 hmac\n");
-		return err;
-	}
-	if (memcmp(&hmac, &report->hmac, sizeof(hash_block_t))) {
-		RTLS_ERR("PEK and ChipId may have been tampered with\n");
-		return err;
-	}
-	RTLS_DEBUG("check PEK and ChipId successfully\n");
-
-	/* Retrieve PEK cert and ChipId */
 	j = (offsetof(csv_attestation_report, reserved1) -
 	     offsetof(csv_attestation_report, pek_cert)) /
 	    sizeof(uint32_t);