Add memutils.c for backend and move existing mem helpers there.

Also remove inline definitions.

lib/crypto_backend/memutils.c

@@ -0,0 +1,46 @@
+/*
+ * Safe memory utilities
+ *
+ * Copyright (C) 2024 Milan Broz
+ *
+ * This file is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This file is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this file; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "crypto_backend_internal.h"
+
+/* Memzero helper (memset on stack can be optimized out) */
+void crypt_backend_memzero(void *s, size_t n)
+{
+#ifdef HAVE_EXPLICIT_BZERO
+	explicit_bzero(s, n);
+#else
+	volatile uint8_t *p = (volatile uint8_t *)s;
+	while(n--) *p++ = 0;
+#endif
+}
+
+/* Internal implementation for constant time memory comparison */
+int crypt_internal_memeq(const void *m1, const void *m2, size_t n)
+{
+	const unsigned char *_m1 = (const unsigned char *) m1;
+	const unsigned char *_m2 = (const unsigned char *) m2;
+	unsigned char result = 0;
+	size_t i;
+
+	for (i = 0; i < n; i++)
+		result |= _m1[i] ^ _m2[i];
+
+	return result;
+}