[nrf noup] bootutil: Add support for KMU stored ED25519 signature key

The commit adds verification of image using keys stored in KMU.

Signed-off-by: Dominik Ermel <[email protected]>
Signed-off-by: Jamie McCrae <[email protected]>

Author: de-nordic

boot/bootutil/src/ed25519_psa.c

@@ -12,16 +12,33 @@
 
 #include <psa/crypto.h>
 #include <psa/crypto_types.h>
+#if defined(CONFIG_BOOT_SIGNATURE_USING_KMU)
+#include <cracen_psa_kmu.h>
+#endif
 
 BOOT_LOG_MODULE_DECLARE(ed25519_psa);
 
 #define SHA512_DIGEST_LENGTH    64
 #define EDDSA_KEY_LENGTH        32
 #define EDDSA_SIGNAGURE_LENGTH  64
 
+#if defined(CONFIG_BOOT_SIGNATURE_USING_KMU)
+/* List of KMU stored key ids available for MCUboot */
+#define MAKE_PSA_KMU_KEY_ID(id) PSA_KEY_HANDLE_FROM_CRACEN_KMU_SLOT(CRACEN_KMU_KEY_USAGE_SCHEME_RAW, id)
+
+static psa_key_id_t kmu_key_ids[] =  {
+    MAKE_PSA_KMU_KEY_ID(226),
+    MAKE_PSA_KMU_KEY_ID(228),
+    MAKE_PSA_KMU_KEY_ID(230)
+};
+
+#define KMU_KEY_COUNT (sizeof(kmu_key_ids)/sizeof(kmu_key_ids[0]))
+#endif
+
+#if !defined(CONFIG_BOOT_SIGNATURE_USING_KMU)
 int ED25519_verify(const uint8_t *message, size_t message_len,
-                          const uint8_t signature[EDDSA_SIGNAGURE_LENGTH],
-                          const uint8_t public_key[EDDSA_KEY_LENGTH])
+                   const uint8_t signature[EDDSA_SIGNAGURE_LENGTH],
+                   const uint8_t public_key[EDDSA_KEY_LENGTH])
 {
     /* Set to any error */
     psa_status_t status = PSA_ERROR_BAD_STATE;
@@ -69,3 +86,39 @@ int ED25519_verify(const uint8_t *message, size_t message_len,
 
     return ret;
 }
+#else
+int ED25519_verify(const uint8_t *message, size_t message_len,
+                          const uint8_t signature[EDDSA_SIGNAGURE_LENGTH],
+                          const uint8_t public_key[EDDSA_KEY_LENGTH])
+{
+    ARG_UNUSED(public_key);
+    /* Set to any error */
+    psa_status_t status = PSA_ERROR_BAD_STATE;
+    int ret = 0;        /* Fail by default */
+
+    /* Initialize PSA Crypto */
+    status = psa_crypto_init();
+    if (status != PSA_SUCCESS) {
+        BOOT_LOG_ERR("PSA crypto init failed %d", status);
+        return 0;
+    }
+
+    status = PSA_ERROR_BAD_STATE;
+
+    for (int i = 0; i < KMU_KEY_COUNT; ++i) {
+        psa_key_id_t kid = kmu_key_ids[i];
+
+        status = psa_verify_message(kid, PSA_ALG_PURE_EDDSA, message,
+                                    message_len, signature,
+                                    EDDSA_SIGNAGURE_LENGTH);
+        if (status == PSA_SUCCESS) {
+            ret = 1;
+            break;
+        }
+
+        BOOT_LOG_ERR("ED25519 signature verification failed %d", status);
+    }
+
+    return ret;
+}
+#endif

boot/bootutil/src/image_ed25519.c

@@ -25,14 +25,15 @@
 #include "bootutil/crypto/sha.h"
 
 #define EDDSA_SIGNATURE_LENGTH 64
-
-static const uint8_t ed25519_pubkey_oid[] = MBEDTLS_OID_ISO_IDENTIFIED_ORG "\x65\x70";
 #define NUM_ED25519_BYTES 32
 
 extern int ED25519_verify(const uint8_t *message, size_t message_len,
                           const uint8_t signature[EDDSA_SIGNATURE_LENGTH],
                           const uint8_t public_key[NUM_ED25519_BYTES]);
 
+#if !defined(CONFIG_BOOT_SIGNATURE_USING_KMU)
+static const uint8_t ed25519_pubkey_oid[] = MBEDTLS_OID_ISO_IDENTIFIED_ORG "\x65\x70";
+
 /*
  * Parse the public key used for signing.
  */
@@ -71,21 +72,25 @@ bootutil_import_key(uint8_t **cp, uint8_t *end)
 
     return 0;
 }
+#endif
 
 fih_ret
 bootutil_verify_sig(uint8_t *hash, uint32_t hlen, uint8_t *sig, size_t slen,
   uint8_t key_id)
 {
     int rc;
     FIH_DECLARE(fih_rc, FIH_FAILURE);
-    uint8_t *pubkey;
+    uint8_t *pubkey = NULL;
+#if !defined(CONFIG_BOOT_SIGNATURE_USING_KMU)
     uint8_t *end;
+#endif
 
     if (hlen != IMAGE_HASH_SIZE || slen != EDDSA_SIGNATURE_LENGTH) {
         FIH_SET(fih_rc, FIH_FAILURE);
         goto out;
     }
 
+#if !defined(CONFIG_BOOT_SIGNATURE_USING_KMU)
     pubkey = (uint8_t *)bootutil_keys[key_id].key;
     end = pubkey + *bootutil_keys[key_id].len;
 
@@ -94,6 +99,7 @@ bootutil_verify_sig(uint8_t *hash, uint32_t hlen, uint8_t *sig, size_t slen,
         FIH_SET(fih_rc, FIH_FAILURE);
         goto out;
     }
+#endif
 
     rc = ED25519_verify(hash, IMAGE_HASH_SIZE, sig, pubkey);
 
@@ -115,14 +121,17 @@ bootutil_verify_img(const uint8_t *img, uint32_t size,
 {
     int rc;
     FIH_DECLARE(fih_rc, FIH_FAILURE);
-    uint8_t *pubkey;
+    uint8_t *pubkey = NULL;
+#if !defined(CONFIG_BOOT_SIGNATURE_USING_KMU)
     uint8_t *end;
+#endif
 
     if (slen != EDDSA_SIGNATURE_LENGTH) {
         FIH_SET(fih_rc, FIH_FAILURE);
         goto out;
     }
 
+#if !defined(CONFIG_BOOT_SIGNATURE_USING_KMU)
     pubkey = (uint8_t *)bootutil_keys[key_id].key;
     end = pubkey + *bootutil_keys[key_id].len;
 
@@ -131,6 +140,7 @@ bootutil_verify_img(const uint8_t *img, uint32_t size,
         FIH_SET(fih_rc, FIH_FAILURE);
         goto out;
     }
+#endif
 
     rc = ED25519_verify(img, size, sig, pubkey);
 

boot/zephyr/CMakeLists.txt

@@ -297,7 +297,7 @@ if(CONFIG_MCUBOOT_SERIAL)
   endif()
 endif()
 
-if(NOT CONFIG_BOOT_SIGNATURE_KEY_FILE STREQUAL "")
+if(NOT CONFIG_BOOT_SIGNATURE_USING_KMU OR NOT CONFIG_BOOT_SIGNATURE_KEY_FILE STREQUAL "")
   # CONF_FILE points to the KConfig configuration files of the bootloader.
   foreach (filepath ${CONF_FILE})
     file(READ ${filepath} temp_text)

boot/zephyr/Kconfig

@@ -302,6 +302,20 @@ endif
 
 endchoice
 
+config BOOT_SIGNATURE_USING_KMU
+	bool "Use KMU stored keys for signature verification"
+	select PSA_WANT_ALG_GCM
+	select PSA_WANT_KEY_TYPE_AES
+	select PSA_WANT_AES_KEY_SIZE_256
+	select PSA_WANT_ALG_SP800_108_COUNTER_CMAC
+	select PSA_WANT_ALG_CMAC
+	select PSA_WANT_ALG_ECB_NO_PADDING
+	help
+	  The MCUboot will use keys provisioned to board for signature verification
+	  instead of compiling in a key data.
+
+if !BOOT_SIGNATURE_USING_KMU
+
 config BOOT_SIGNATURE_KEY_FILE
 	string "PEM key file"
 	default "root-ec-p256.pem" if BOOT_SIGNATURE_TYPE_ECDSA_P256
@@ -319,6 +333,8 @@ config BOOT_SIGNATURE_KEY_FILE
 	  with the public key information will be written in a format expected by
 	  MCUboot.
 
+endif
+
 config MCUBOOT_CLEANUP_ARM_CORE
 	bool "Perform core cleanup before chain-load the application"
 	depends on CPU_CORTEX_M