MinSFI: Passing arguments to the entry function

src/minsfi/trusted/entry.c

Index: src/minsfi/trusted/entry.c
diff --git a/src/minsfi/trusted/entry.c b/src/minsfi/trusted/entry.c
index 9a71d9ebc0c01b75db83ac759904c0fb45162fc8..fd8527b26cea379742084990cd7399f81f8ceaf3 100644
--- a/src/minsfi/trusted/entry.c
+++ b/src/minsfi/trusted/entry.c
@@ -4,8 +4,11 @@
  * found in the LICENSE file.
  */
 
+#include <string.h>
+
 #include "native_client/src/include/minsfi.h"
 #include "native_client/src/include/minsfi_priv.h"
+#include "native_client/src/include/minsfi_ptr.h"
 
 /*
  * Fixed offset of the data segment. This must be kept in sync with the
@@ -19,7 +22,7 @@ extern const char  __sfi_data_segment[];
 extern uint32_t    __sfi_data_segment_size;
 
 /* Entry point of the sandbox */
-extern uint32_t _start_minsfi(uint32_t info);
+extern uint32_t _start_minsfi(sfiptr_t info);
 
 static inline void GetManifest(MinsfiManifest *sb) {
   sb->ptr_size = __sfi_pointer_size;
@@ -43,11 +46,73 @@ bool MinsfiInitializeSandbox(void) {
   return true;
 }
 
-int MinsfiInvokeSandbox(void) {
-  if (MinsfiGetActiveSandbox() == NULL)
+/*
+ * Arguments are passed to the sandbox with a single pointer to an array of
+ * integers called 'info' where:
+ *   info[0] = argc
+ *   info[j+1] = untrusted pointer to argv[j]      (for 0 <= j < argc)
+ * The sandbox will expect this array to be stored at the bottom of the
+ * untrusted stack and will start growing the stack backwards from the given
+ * address.
+ *
+ * This function will iterate over the arguments, store the argv[*] strings
+ * at the bottom of the untrusted stack and prepend it with the 'info' data
+ * structure as described above.
+ */
+static sfiptr_t CopyArguments(int argc, char *argv[], const MinsfiSandbox *sb) {
+  int arg_index;
+  size_t arg_length, info_length;
+  sfiptr_t *info;
+  char *stack_base, *stack_ptr;
+
+  if (argc < 0)
+    return 0;
+
+  /* Allocate memory for the info data structure. */
+  info_length = (argc + 1) * sizeof(sfiptr_t);
+  info = (sfiptr_t*) malloc(info_length);
+  info[0] = argc;
+
+  /* Compute the bounds of the stack. */
+  stack_base = sb->mem_base + sb->mem_layout.stack.offset;
+  stack_ptr = stack_base + sb->mem_layout.stack.length;
+
+  /* Copy the argv[*] strings onto the stack. Return NULL if the stack is not
+   * large enough. */
+  for (arg_index = 0; arg_index < argc; ++arg_index) {
+    arg_length = strlen(argv[arg_index]) + 1;
+    stack_ptr -= arg_length;
+    if (stack_ptr < stack_base)
+      return 0;

[jvoung (off chromium), 2014/09/10 17:04:29]

free(info), on early exit?

[dbrazdil, 2014/09/10 18:49:47]

Done. Thanks

+
+    memcpy(stack_ptr, argv[arg_index], arg_length);
+    info[arg_index + 1] = ToMinsfiPtr(stack_ptr, sb);
+  }
+
+  /* Copy the info data structure across. */
+  stack_ptr -= info_length;
+  if (stack_ptr < stack_base)
+    return 0;

[jvoung (off chromium), 2014/09/10 17:04:29]

free(info)?

[dbrazdil, 2014/09/10 18:49:47]

Done.

+  memcpy(stack_ptr, (char*) info, info_length);
+
+  /* Clean up. */
+  free(info);
+
+  /* Return untrusted pointer to the beginning of the data structure. */
+  return ToMinsfiPtr(stack_ptr, sb);
+}
+
+int MinsfiInvokeSandbox(int argc, char *argv[]) {
+  const MinsfiSandbox *sb;
+  sfiptr_t info;
+
+  if ((sb = MinsfiGetActiveSandbox()) == NULL)
+    return EXIT_FAILURE;
+
+  if ((info = CopyArguments(argc, argv, sb)) == 0)
     return EXIT_FAILURE;
 
-  return _start_minsfi(0);
+  return _start_minsfi(info);
 }
 
 bool MinsfiDestroySandbox(void) {