TBB: add non-volatile counter support

This patch adds support for non-volatile counter authentication to
the Authentication Module. This method consists of matching the
counter values provided in the certificates with the ones stored
in the platform. If the value from the certificate is lower than
the platform, the boot process is aborted. This mechanism protects
the system against rollback.

The TBBR CoT has been updated to include this method as part of the
authentication process. Two counters are used: one for the trusted
world images and another for the non trusted world images.

** NEW PLATFORM APIs (mandatory when TBB is enabled) **

int plat_get_nv_ctr(void *cookie, unsigned int *nv_ctr);

    This API returns the non-volatile counter value stored
    in the platform. The cookie in the first argument may be
    used to select the counter in case the platform provides
    more than one (i.e. TBSA compliant platforms must provide
    trusted and non-trusted counters). This cookie is specified
    in ...

docs/porting-guide.md

@@ -638,6 +638,35 @@ retrieved from the platform. The function also reports extra information related
 to the ROTPK in the flags parameter.
 
 
+### Function: plat_get_nv_ctr()
+
+    Argument : void *, unsigned int *
+    Return   : int
+
+This function is mandatory when Trusted Board Boot is enabled. It returns the
+non-volatile counter value stored in the platform in the second argument. The
+cookie in the first argument may be used to select the counter in case the
+platform provides more than one (for example, on platforms that use the default
+TBBR CoT, the cookie will correspond to the OID values defined in
+TRUSTED_FW_NVCOUNTER_OID or NON_TRUSTED_FW_NVCOUNTER_OID).
+
+The function returns 0 on success. Any other value means the counter value could
+not be retrieved from the platform.
+
+
+### Function: plat_set_nv_ctr()
+
+    Argument : void *, unsigned int
+    Return   : int
+
+This function is mandatory when Trusted Board Boot is enabled. It sets a new
+counter value in the platform. The cookie in the first argument may be used to
+select the counter (as explained in plat_get_nv_ctr()).
+
+The function returns 0 on success. Any other value means the counter value could
+not be updated.
+
+
 2.3 Common mandatory modifications
 ---------------------------------
 

drivers/auth/auth_mod.c

@@ -40,6 +40,9 @@
 #include <stdint.h>
 #include <string.h>
 
+/* ASN.1 tags */
+#define ASN1_INTEGER                 0x02
+
 #define return_if_error(rc) \
 	do { \
 		if (rc != 0) { \
@@ -226,6 +229,83 @@ static int auth_signature(const auth_method_param_sig_t *param,
 	return rc;
 }
 
+/*
+ * Authenticate by Non-Volatile counter
+ *
+ * To protect the system against rollback, the platform includes a non-volatile
+ * counter whose value can only be increased. All certificates include a counter
+ * value that should not be lower than the value stored in the platform. If the
+ * value is larger, the counter in the platform must be updated to the new
+ * value.
+ *
+ * Return: 0 = success, Otherwise = error
+ */
+static int auth_nvctr(const auth_method_param_nv_ctr_t *param,
+		      const auth_img_desc_t *img_desc,
+		      void *img, unsigned int img_len)
+{
+	char *p;
+	void *data_ptr = NULL;
+	unsigned int data_len, len, i;
+	unsigned int cert_nv_ctr, plat_nv_ctr;
+	int rc = 0;
+
+	/* Get the counter value from current image. The AM expects the IPM
+	 * to return the counter value as a DER encoded integer */
+	rc = img_parser_get_auth_param(img_desc->img_type, param->cert_nv_ctr,
+				       img, img_len, &data_ptr, &data_len);
+	return_if_error(rc);
+
+	/* Parse the DER encoded integer */
+	assert(data_ptr);
+	p = (char *)data_ptr;
+	if (*p != ASN1_INTEGER) {
+		/* Invalid ASN.1 integer */
+		return 1;
+	}
+	p++;
+
+	/* NV-counters are unsigned integers up to 32-bit */
+	len = (unsigned int)(*p & 0x7f);
+	if ((*p & 0x80) || (len > 4)) {
+		return 1;
+	}
+	p++;
+
+	/* Check the number is not negative */
+	if (*p & 0x80) {
+		return 1;
+	}
+
+	/* Convert to unsigned int. This code is for a little-endian CPU */
+	cert_nv_ctr = 0;
+	for (i = 0; i < len; i++) {
+		cert_nv_ctr = (cert_nv_ctr << 8) | *p++;
+	}
+
+	/* Get the counter from the platform */
+	rc = plat_get_nv_ctr(param->plat_nv_ctr->cookie, &plat_nv_ctr);
+	return_if_error(rc);
+
+	if (cert_nv_ctr < plat_nv_ctr) {
+		/* Invalid NV-counter */
+		return 1;
+	} else if (cert_nv_ctr > plat_nv_ctr) {
+		if (img_desc->parent == NULL) {
+			/* This certificate has been signed with the ROT key.
+			 * Update the platform counter value */
+			rc = plat_set_nv_ctr(param->plat_nv_ctr->cookie,
+					     cert_nv_ctr);
+			return_if_error(rc);
+		} else {
+			/* Secondary certificates cannot modify the counter */
+			return 1;
+		}
+	}
+
+	return 0;
+}
+
 /*
  * Return the parent id in the output parameter '*parent_id'
  *
@@ -310,6 +390,10 @@ int auth_mod_verify_img(unsigned int img_id,
 			rc = auth_signature(&auth_method->param.sig,
 					img_desc, img_ptr, img_len);
 			break;
+		case AUTH_METHOD_NV_CTR:
+			rc = auth_nvctr(&auth_method->param.nv_ctr,
+					img_desc, img_ptr, img_len);
+			break;
 		default:
 			/* Unknown authentication method */
 			rc = 1;

drivers/auth/mbedtls/mbedtls_x509_parser.c

@@ -405,6 +405,13 @@ static int check_integrity(void *img, unsigned int img_len)
 
 /*
  * Extract an authentication parameter from an X509v3 certificate
+ *
+ * This function returns a pointer to the extracted data and its length.
+ * Depending on the type of parameter, a pointer to the data stored in the
+ * certificate may be returned (i.e. an octet string containing a hash). Other
+ * data may need to be copied and formatted (i.e. integers). In the later case,
+ * a buffer of the correct type needs to be statically allocated, filled and
+ * returned.
  */
 static int get_auth_param(const auth_param_type_desc_t *type_desc,
 		void *img, unsigned int img_len,
@@ -422,6 +429,7 @@ static int get_auth_param(const auth_param_type_desc_t *type_desc,
 		*param_len = (unsigned int)tbs.len;
 		break;
 	case AUTH_PARAM_HASH:
+	case AUTH_PARAM_NV_CTR:
 		/* All these parameters are included as X509v3 extensions */
 		rc = get_ext(type_desc->cookie, param, param_len);
 		break;

drivers/auth/tbbr/tbbr_cot.c

@@ -56,6 +56,11 @@ static unsigned char content_pk_buf[PK_DER_LEN];
 /*
  * Parameter type descriptors
  */
+static auth_param_type_desc_t trusted_nv_ctr = AUTH_PARAM_TYPE_DESC(
+		AUTH_PARAM_NV_CTR, TRUSTED_FW_NVCOUNTER_OID);
+static auth_param_type_desc_t non_trusted_nv_ctr = AUTH_PARAM_TYPE_DESC(
+		AUTH_PARAM_NV_CTR, NON_TRUSTED_FW_NVCOUNTER_OID);
+
 static auth_param_type_desc_t subject_pk = AUTH_PARAM_TYPE_DESC(
 		AUTH_PARAM_PUB_KEY, 0);
 static auth_param_type_desc_t sig = AUTH_PARAM_TYPE_DESC(
@@ -116,6 +121,13 @@ static const auth_img_desc_t cot_desc[] = {
 					.alg = &sig_alg,
 					.data = &raw_data,
 				}
+			},
+			[1] = {
+				.type = AUTH_METHOD_NV_CTR,
+				.param.nv_ctr = {
+					.cert_nv_ctr = &trusted_nv_ctr,
+					.plat_nv_ctr = &trusted_nv_ctr
+				}
 			}
 		},
 		.authenticated_data = {
@@ -158,6 +170,13 @@ static const auth_img_desc_t cot_desc[] = {
 					.alg = &sig_alg,
 					.data = &raw_data,
 				}
+			},
+			[1] = {
+				.type = AUTH_METHOD_NV_CTR,
+				.param.nv_ctr = {
+					.cert_nv_ctr = &trusted_nv_ctr,
+					.plat_nv_ctr = &trusted_nv_ctr
+				}
 			}
 		},
 		.authenticated_data = {
@@ -193,6 +212,13 @@ static const auth_img_desc_t cot_desc[] = {
 					.alg = &sig_alg,
 					.data = &raw_data,
 				}
+			},
+			[1] = {
+				.type = AUTH_METHOD_NV_CTR,
+				.param.nv_ctr = {
+					.cert_nv_ctr = &trusted_nv_ctr,
+					.plat_nv_ctr = &trusted_nv_ctr
+				}
 			}
 		},
 		.authenticated_data = {
@@ -218,6 +244,13 @@ static const auth_img_desc_t cot_desc[] = {
 					.alg = &sig_alg,
 					.data = &raw_data,
 				}
+			},
+			[1] = {
+				.type = AUTH_METHOD_NV_CTR,
+				.param.nv_ctr = {
+					.cert_nv_ctr = &trusted_nv_ctr,
+					.plat_nv_ctr = &trusted_nv_ctr
+				}
 			}
 		},
 		.authenticated_data = {
@@ -260,6 +293,13 @@ static const auth_img_desc_t cot_desc[] = {
 					.alg = &sig_alg,
 					.data = &raw_data,
 				}
+			},
+			[1] = {
+				.type = AUTH_METHOD_NV_CTR,
+				.param.nv_ctr = {
+					.cert_nv_ctr = &trusted_nv_ctr,
+					.plat_nv_ctr = &trusted_nv_ctr
+				}
 			}
 		},
 		.authenticated_data = {
@@ -285,6 +325,13 @@ static const auth_img_desc_t cot_desc[] = {
 					.alg = &sig_alg,
 					.data = &raw_data,
 				}
+			},
+			[1] = {
+				.type = AUTH_METHOD_NV_CTR,
+				.param.nv_ctr = {
+					.cert_nv_ctr = &trusted_nv_ctr,
+					.plat_nv_ctr = &trusted_nv_ctr
+				}
 			}
 		},
 		.authenticated_data = {
@@ -327,6 +374,13 @@ static const auth_img_desc_t cot_desc[] = {
 					.alg = &sig_alg,
 					.data = &raw_data,
 				}
+			},
+			[1] = {
+				.type = AUTH_METHOD_NV_CTR,
+				.param.nv_ctr = {
+					.cert_nv_ctr = &trusted_nv_ctr,
+					.plat_nv_ctr = &trusted_nv_ctr
+				}
 			}
 		},
 		.authenticated_data = {
@@ -352,6 +406,13 @@ static const auth_img_desc_t cot_desc[] = {
 					.alg = &sig_alg,
 					.data = &raw_data,
 				}
+			},
+			[1] = {
+				.type = AUTH_METHOD_NV_CTR,
+				.param.nv_ctr = {
+					.cert_nv_ctr = &trusted_nv_ctr,
+					.plat_nv_ctr = &trusted_nv_ctr
+				}
 			}
 		},
 		.authenticated_data = {
@@ -394,6 +455,13 @@ static const auth_img_desc_t cot_desc[] = {
 					.alg = &sig_alg,
 					.data = &raw_data,
 				}
+			},
+			[1] = {
+				.type = AUTH_METHOD_NV_CTR,
+				.param.nv_ctr = {
+					.cert_nv_ctr = &non_trusted_nv_ctr,
+					.plat_nv_ctr = &non_trusted_nv_ctr
+				}
 			}
 		},
 		.authenticated_data = {
@@ -419,6 +487,13 @@ static const auth_img_desc_t cot_desc[] = {
 					.alg = &sig_alg,
 					.data = &raw_data,
 				}
+			},
+			[1] = {
+				.type = AUTH_METHOD_NV_CTR,
+				.param.nv_ctr = {
+					.cert_nv_ctr = &non_trusted_nv_ctr,
+					.plat_nv_ctr = &non_trusted_nv_ctr
+				}
 			}
 		},
 		.authenticated_data = {

include/drivers/auth/auth_common.h

@@ -46,6 +46,7 @@ typedef enum auth_param_type_enum {
 	AUTH_PARAM_SIG_ALG,		/* The image signature algorithm */
 	AUTH_PARAM_HASH,		/* A hash (including the algorithm) */
 	AUTH_PARAM_PUB_KEY,		/* A public key */
+	AUTH_PARAM_NV_CTR,		/* A non-volatile counter */
 } auth_param_type_t;
 
 /*
@@ -80,6 +81,7 @@ typedef enum auth_method_type_enum {
 	AUTH_METHOD_NONE = 0,
 	AUTH_METHOD_HASH,	/* Authenticate by hash matching */
 	AUTH_METHOD_SIG,	/* Authenticate by PK operation */
+	AUTH_METHOD_NV_CTR,	/* Authenticate by Non-Volatile Counter */
 	AUTH_METHOD_NUM 	/* Number of methods */
 } auth_method_type_t;
 
@@ -105,7 +107,8 @@ typedef struct auth_method_param_sig_s {
  * Parameters for authentication by NV counter
  */
 typedef struct auth_method_param_nv_ctr_s {
-	auth_param_type_desc_t *nv_ctr;	/* NV counter value */
+	auth_param_type_desc_t *cert_nv_ctr;	/* NV counter in certificate */
+	auth_param_type_desc_t *plat_nv_ctr;	/* NV counter in platform */
 } auth_method_param_nv_ctr_t;
 
 /*

include/plat/arm/soc/common/soc_css_def.h

@@ -65,6 +65,13 @@
  */
 #define SOC_CSS_NIC400_APB4_BRIDGE	4
 
+/* Non-volatile counters */
+#define SOC_TRUSTED_NVCTR_BASE		0x7fe70000
+#define TFW_NVCTR_BASE			(SOC_TRUSTED_NVCTR_BASE + 0x0000)
+#define TFW_NVCTR_SIZE			4
+#define NTFW_CTR_BASE			(SOC_TRUSTED_NVCTR_BASE + 0x0004)
+#define NTFW_CTR_SIZE			4
+
 /* Keys */
 #define SOC_KEYS_BASE			0x7fe80000
 #define TZ_PUB_KEY_HASH_BASE		(SOC_KEYS_BASE + 0x0000)

include/plat/common/platform.h

@@ -249,6 +249,8 @@ void bl32_plat_enable_mmu(uint32_t flags);
  ******************************************************************************/
 int plat_get_rotpk_info(void *cookie, void **key_ptr, unsigned int *key_len,
 			unsigned int *flags);
+int plat_get_nv_ctr(void *cookie, unsigned int *nv_ctr);
+int plat_set_nv_ctr(void *cookie, unsigned int nv_ctr);
 
 #if ENABLE_PLAT_COMPAT
 /*

plat/arm/board/common/board_arm_trusted_boot.c

@@ -31,11 +31,14 @@
 #include <arm_def.h>
 #include <assert.h>
 #include <platform.h>
+#include <platform_oid.h>
 #include <stdint.h>
 #include <string.h>
 
 /* Weak definition may be overridden in specific platform */
 #pragma weak plat_match_rotpk
+#pragma weak plat_get_nv_ctr
+#pragma weak plat_set_nv_ctr
 
 /* SHA256 algorithm */
 #define SHA256_BYTES			32
@@ -148,3 +151,43 @@ int plat_get_rotpk_info(void *cookie, void **key_ptr, unsigned int *key_len,
 	return 0;
 }
 
+/*
+ * Return the non-volatile counter value stored in the platform. The cookie
+ * will contain the OID of the counter in the certificate.
+ *
+ * Return: 0 = success, Otherwise = error
+ */
+int plat_get_nv_ctr(void *cookie, unsigned int *nv_ctr)
+{
+	const char *oid;
+	uint32_t *nv_ctr_addr;
+
+	assert(cookie != NULL);
+	assert(nv_ctr != NULL);
+
+	oid = (const char *)cookie;
+	if (strcmp(oid, TRUSTED_FW_NVCOUNTER_OID) == 0) {
+		nv_ctr_addr = (uint32_t *)TFW_NVCTR_BASE;
+	} else if (strcmp(oid, NON_TRUSTED_FW_NVCOUNTER_OID) == 0) {
+		nv_ctr_addr = (uint32_t *)NTFW_CTR_BASE;
+	} else {
+		return 1;
+	}
+
+	*nv_ctr = (unsigned int)(*nv_ctr_addr);
+
+	return 0;
+}
+
+/*
+ * Store a new non-volatile counter value. On Juno and FVP, the non-volatile
+ * counters are RO and cannot be modified. We expect the values in the
+ * certificates to always match the RO values so that this function is never
+ * called.
+ *
+ * Return: 0 = success, Otherwise = error
+ */
+int plat_set_nv_ctr(void *cookie, unsigned int nv_ctr)
+{
+	return 1;
+}

plat/arm/board/common/board_common.mk

@@ -51,6 +51,11 @@ ifneq (${TRUSTED_BOARD_BOOT},0)
     endif
     $(eval $(call add_define,ARM_ROTPK_LOCATION_ID))
 
+    # Certificate NV-Counters. Use values corresponding to tied off values in
+    # ARM development platforms
+    TFW_NVCTR_VAL	?=	31
+    NTFW_NVCTR_VAL	?=	223
+
     BL1_SOURCES		+=	plat/arm/board/common/board_arm_trusted_boot.c
     BL2_SOURCES		+=	plat/arm/board/common/board_arm_trusted_boot.c
 endif

plat/arm/board/fvp/fvp_def.h

@@ -69,7 +69,13 @@
 
 #define PCIE_EXP_BASE			0x40000000
 #define TZRNG_BASE			0x7fe60000
-#define TZNVCTR_BASE			0x7fe70000
+
+/* Non-volatile counters */
+#define TRUSTED_NVCTR_BASE		0x7fe70000
+#define TFW_NVCTR_BASE			(TRUSTED_NVCTR_BASE + 0x0000)
+#define TFW_NVCTR_SIZE			4
+#define NTFW_CTR_BASE			(TRUSTED_NVCTR_BASE + 0x0004)
+#define NTFW_CTR_SIZE			4
 
 /* Keys */
 #define SOC_KEYS_BASE			0x7fe80000