Avoid fallback to weak entropy for the PRNGs on Windows.

Add fallback to rand_s() to gather entropy on Windows for
seeding the random number generator. This is compatible
with what Blink does.

BUG=v8:2905
R=machenbach@chromium.org

Review URL: https://codereview.chromium.org/24315007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16920 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/utils/random-number-generator.cc

@@ -28,6 +28,7 @@
 #include "utils/random-number-generator.h"
 
 #include <cstdio>
+#include <cstdlib>
 
 #include "flags.h"
 #include "platform/mutex.h"
@@ -67,6 +68,16 @@ RandomNumberGenerator::RandomNumberGenerator() {
     }
   }
 
+#if V8_OS_CYGWIN || V8_OS_WIN
+  // Use rand_s() to gather entropy on Windows. See:
+  // https://code.google.com/p/v8/issues/detail?id=2905
+  unsigned first_half, second_half;
+  errno_t result = rand_s(&first_half);
+  ASSERT_EQ(0, result);
+  result = rand_s(&second_half);
+  ASSERT_EQ(0, result);
+  SetSeed((static_cast<int64_t>(first_half) << 32) + second_half);
+#else
   // Gather entropy from /dev/urandom if available.
   FILE* fp = fopen("/dev/urandom", "rb");
   if (fp != NULL) {
@@ -91,6 +102,7 @@ RandomNumberGenerator::RandomNumberGenerator() {
   seed ^= TimeTicks::HighResNow().ToInternalValue() << 16;
   seed ^= TimeTicks::Now().ToInternalValue() << 8;
   SetSeed(seed);
+#endif  // V8_OS_CYGWIN || V8_OS_WIN
 }
 
 

tools/gyp/v8.gyp

@@ -805,6 +805,9 @@
           ]},
         ],
         ['OS=="win"', {
+          'defines': [
+            '_CRT_RAND_S'  # for rand_s()
+          ],
           'variables': {
             'gyp_generators': '<!(echo $GYP_GENERATORS)',
           },