bootutil: Support for MCUBOOT_BYPASS_KEY_MATCH

This MCUboot configuration option turns off matching of
public key hash, taken from image TLV, against built in public
key. Such verification is not needed when there is only one
key built in as the signature verification will reject
image signed with unknown key anyway.
Enabling the option allows to slightly reduce MCUboot binary
size by removing the code that does the key matching.
Boot time improvement is not really significant.

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>

Author: de-nordic

boot/bootutil/src/image_validate.c

@@ -280,6 +280,8 @@ bootutil_img_hash(struct boot_loader_state *state,
 #   define KEY_BUF_SIZE         (SIG_BUF_SIZE + 24)
 #endif /* !MCUBOOT_HW_KEY */
 
+#if !defined(MCUBOOT_BYPASS_KEY_MATCH)
+/* Find functions are only needed when key is checked first */
 #if !defined(MCUBOOT_HW_KEY)
 static int
 bootutil_find_key(uint8_t *keyhash, uint8_t keyhash_len)
@@ -349,6 +351,18 @@ bootutil_find_key(uint8_t image_index, uint8_t *key, uint16_t key_len)
 #endif /* !MCUBOOT_HW_KEY */
 #endif /* !MCUBOOT_BUILTIN_KEY */
 #endif /* EXPECTED_SIG_TLV */
+#else  /* !MCUBOOT_BYPASS_KEY_MATCH */
+static inline int
+bootutil_find_key(uint8_t image_index, uint8_t *key, uint16_t key_len)
+{
+    (void)image_index;
+    (void)key;
+    (void)key_len;
+
+    /* There is only one key, so it always matches */
+    return 0;
+}
+#endif /* !MCUBOOT_BYPASS_KEY_MATCH */
 
 /**
  * Reads the value of an image's security counter.