Add a StatefulMemcpy which can be used to safely and iteratively copy blocks of memory.

Review URL: http://codereview.chromium.org/572024

include/utility.h

@@ -10,6 +10,7 @@
 #ifndef VBOOT_REFERENCE_UTILITY_H_
 #define VBOOT_REFERENCE_UTILITY_H_
 
+#include <inttypes.h>
 #include <string.h>
 
 /* Allocate [size] bytes and return a pointer to the allocated memory. Abort
@@ -23,10 +24,30 @@ void Free(void* ptr);
 /* Copy [n] bytes from [src] to [dest]. */
 void* Memcpy(void* dest, const void* src, size_t n);
 
+/* Set [n] bytes starting at [s] to [c]. */
+void* Memset(void *dest, const uint8_t c, size_t n);
+
 /* Compare [n] bytes starting at [s1] with [s2] and return 1 if they match,
  * 0 if they don't. Time taken to perform the comparison is only dependent on
  * [n] and not on the relationship of the match between [s1] and [s2].
  */
 int SafeMemcmp(const void* s1, const void* s2, size_t n);
 
+/* Track remaining data to be read in a buffer. */
+typedef struct MemcpyState {
+  void* remaining_buf;
+  int remaining_len;
+} MemcpyState;
+
+/* Copy [len] bytes into [dst] only if there's enough data to read according
+ * to [state].
+ * On success, return [dst] and update [state]..
+ * On failure, return NULL, set remaining len in state to -1.
+ *
+ * Useful for iterating through a binary blob to populate a struct. After the
+ * first failure (buffer overrun), successive calls will always fail.
+ */
+void* StatefulMemcpy(MemcpyState* state, void* dst, int len);
+
+
 #endif  /* VBOOT_REFERENCE_UTILITY_H_ */