diff --git a/sys/compat/linuxkpi/common/include/linux/string.h b/sys/compat/linuxkpi/common/include/linux/string.h
--- a/sys/compat/linuxkpi/common/include/linux/string.h
+++ b/sys/compat/linuxkpi/common/include/linux/string.h
@@ -98,6 +98,18 @@
 	return (dst);
 }
 
+/* See slab.h for kvmalloc/kvfree(). */
+static inline void *
+kvmemdup(const void *src, size_t len, gfp_t gfp)
+{
+	void *dst;
+
+	dst = kvmalloc(len, gfp);
+	if (dst != NULL)
+		memcpy(dst, src, len);
+	return (dst);
+}
+
 static inline char *
 strndup_user(const char __user *ustr, long n)
 {