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

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

common/utility_stub.c

@@ -10,7 +10,6 @@
 
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
 
 void* Malloc(size_t size) {
   void* p = malloc(size);
@@ -29,6 +28,13 @@ void* Memcpy(void* dest, const void* src, size_t n) {
   return memcpy(dest, src, n);
 }
 
+void* Memset(void* dest, const uint8_t c, size_t n) {
+  while (n--) {
+    *((uint8_t*)dest) = c;
+  }
+  return dest;
+}
+
 int SafeMemcmp(const void* s1, const void* s2, size_t n) {
   int match = 1;
   const unsigned char* us1 = s1;
@@ -42,3 +48,16 @@ int SafeMemcmp(const void* s1, const void* s2, size_t n) {
 
   return match;
 }
+
+void* StatefulMemcpy(MemcpyState* state, void* dst, int len) {
+  void* saved_ptr;
+  if (len > state->remaining_len) {
+    state->remaining_len = -1;
+    return NULL;
+  }
+  saved_ptr = state->remaining_buf;
+  Memcpy(dst, saved_ptr, len);
+  state->remaining_buf += len;
+  state->remaining_len -= len;
+  return dst;
+}

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_ */

utils/Makefile

@@ -8,6 +8,5 @@ all:	dumpRSAPublicKey
 
 dumpRSAPublicKey:	dumpRSAPublicKey.c
 		$(CC) $(CFLAGS) $(LIBS) $< -o $@
-
 clean:
 	rm -f dumpRSAPublicKey