core: make constant compare common

Move wolfBoot_constant_compare out of TPM-only code so AHCI and update paths can use it without TPM feature gating.

F/CI

Author: danielinux

include/image.h

@@ -1254,6 +1254,7 @@ static void UNUSEDFUNCTION wolfBoot_image_clear_signature_ok(
 /* Defined in image.c */
 int image_CT_compare(const uint8_t *expected, const uint8_t *actual,
     uint32_t len);
+int wolfBoot_constant_compare(const uint8_t* a, const uint8_t* b, uint32_t len);
 int wolfBoot_open_image(struct wolfBoot_image *img, uint8_t part);
 #ifdef EXT_FLASH
 int wolfBoot_open_image_external(struct wolfBoot_image* img, uint8_t part, uint8_t* addr);

include/tpm.h

@@ -79,10 +79,6 @@ int wolfBoot_load_pubkey(const uint8_t* pubkey_hint, WOLFTPM2_KEY* pubKey,
     TPM_ALG_ID* pAlg);
 #endif
 
-#if defined(WOLFBOOT_TPM_KEYSTORE) || defined(WOLFBOOT_TPM_SEAL)
-int wolfBoot_constant_compare(const uint8_t* a, const uint8_t* b, uint32_t len);
-#endif
-
 #ifdef WOLFBOOT_TPM_KEYSTORE
 int wolfBoot_check_rot(int key_slot, uint8_t* pubkey_hint);
 #endif

src/string.c

@@ -223,6 +223,18 @@ int memcmp(const void *_s1, const void *_s2, size_t n)
     return diff;
 }
 
+int wolfBoot_constant_compare(const uint8_t* a, const uint8_t* b, uint32_t len)
+{
+    uint32_t i;
+    uint8_t diff = 0;
+
+    for (i = 0; i < len; i++) {
+        diff |= a[i] ^ b[i];
+    }
+
+    return diff;
+}
+
 void* memchr(void const *s, int c_in, size_t n)
 {
     unsigned char c = (unsigned char)c_in;

src/tpm.c

@@ -44,19 +44,6 @@ WOLFTPM2_KEY     wolftpm_srk;
 #endif
 
 #if defined(WOLFBOOT_TPM_SEAL) || defined(WOLFBOOT_TPM_KEYSTORE)
-int wolfBoot_constant_compare(const uint8_t* a, const uint8_t* b,
-    uint32_t len)
-{
-    uint32_t i;
-    uint8_t diff = 0;
-
-    for (i = 0; i < len; i++) {
-        diff |= a[i] ^ b[i];
-    }
-
-    return diff;
-}
-
 void wolfBoot_print_hexstr(const unsigned char* bin, unsigned long sz,
     unsigned long maxLine)
 {