v8-randomize-hash.patch

From db8adac19321504530e6794771ae534a238c1648 Mon Sep 17 00:00:00 2001
From: Bert Belder <bertbelder@gmail.com>
Date: Fri, 30 Dec 2011 14:36:31 +0100
Subject: [PATCH 1/1] Partial support for hash randomization

- Doesn't play nice with snapshots
- Breaks ARM and MIPS
---
 deps/v8/src/flag-definitions.h      |    3 +++
 deps/v8/src/ia32/code-stubs-ia32.cc |   18 ++++++++++++++----
 deps/v8/src/isolate.cc              |    8 +++++++-
 deps/v8/src/isolate.h               |    3 +++
 deps/v8/src/objects-inl.h           |    6 ++++--
 deps/v8/src/objects.cc              |    4 +++-
 deps/v8/src/x64/code-stubs-x64.cc   |   18 ++++++++++++++----
 7 files changed, 48 insertions(+), 12 deletions(-)

diff --git a/deps/v8/src/flag-definitions.h b/deps/v8/src/flag-definitions.h
index 7df2b0b..e0b3989 100644
--- a/deps/v8/src/flag-definitions.h
+++ b/deps/v8/src/flag-definitions.h
@@ -319,6 +319,9 @@ DEFINE_bool(trace_exception, false,
             "print stack trace when throwing exceptions")
 DEFINE_bool(preallocate_message_memory, false,
             "preallocate some memory to build stack traces.")
+DEFINE_bool(randomize_string_hashes,
+            true,
+            "randomize string hashes to avoid predictable hash collisions")
 
 // v8.cc
 DEFINE_bool(preemption, false,
diff --git a/deps/v8/src/ia32/code-stubs-ia32.cc b/deps/v8/src/ia32/code-stubs-ia32.cc
index 1009aaf..444fd28 100644
--- a/deps/v8/src/ia32/code-stubs-ia32.cc
+++ b/deps/v8/src/ia32/code-stubs-ia32.cc
@@ -5606,10 +5606,20 @@ void StringHelper::GenerateHashInit(MacroAssembler* masm,
                                     Register hash,
                                     Register character,
                                     Register scratch) {
-  // hash = character + (character << 10);
-  __ mov(hash, character);
-  __ shl(hash, 10);
-  __ add(hash, Operand(character));
+  int32_t seed = masm->isolate()->HasherSeed();
+  if (seed != 0) {
+    ASSERT(FLAG_randomize_string_hashes);
+    // hash = (seed + character) + ((seed + character) << 10);
+    __ lea(scratch, Operand(character, seed));
+    __ shl(scratch, 10);
+    __ lea(hash, Operand(hash, character, times_1, seed));
+  } else {
+    ASSERT(!FLAG_randomize_string_hashes);
+    // hash = character + (character << 10);
+    __ mov(hash, character);
+    __ shl(hash, 10);
+    __ add(hash, Operand(character));
+  }
   // hash ^= hash >> 6;
   __ mov(scratch, hash);
   __ sar(scratch, 6);
diff --git a/deps/v8/src/isolate.cc b/deps/v8/src/isolate.cc
index fd0f673..b24e474 100644
--- a/deps/v8/src/isolate.cc
+++ b/deps/v8/src/isolate.cc
@@ -1410,7 +1410,8 @@ Isolate::Isolate()
       thread_manager_(NULL),
       string_tracker_(NULL),
       regexp_stack_(NULL),
-      embedder_data_(NULL) {
+      embedder_data_(NULL),
+      hasher_seed_(0) {
   TRACE_ISOLATE(constructor);
 
   memset(isolate_addresses_, 0,
@@ -1709,6 +1710,11 @@ bool Isolate::Init(Deserializer* des) {
   regexp_stack_ = new RegExpStack();
   regexp_stack_->isolate_ = this;
 
+  // Setup the seed that is used to randomize the string hash function.
+  if (FLAG_randomize_string_hashes) {
+    hasher_seed_ = V8::RandomPrivate(this);
+  }
+
   // Enable logging before setting up the heap
   logger_->Setup();
 
diff --git a/deps/v8/src/isolate.h b/deps/v8/src/isolate.h
index 2582da6..a75342c 100644
--- a/deps/v8/src/isolate.h
+++ b/deps/v8/src/isolate.h
@@ -897,6 +897,8 @@ class Isolate {
     return &interp_canonicalize_mapping_;
   }
 
+  uint32_t HasherSeed() { return hasher_seed_; }
+
   void* PreallocatedStorageNew(size_t size);
   void PreallocatedStorageDelete(void* p);
   void PreallocatedStorageInit(size_t size);
@@ -1149,6 +1151,7 @@ class Isolate {
   RegExpStack* regexp_stack_;
   unibrow::Mapping<unibrow::Ecma262Canonicalize> interp_canonicalize_mapping_;
   void* embedder_data_;
+  uint32_t hasher_seed_;
 
 #if defined(V8_TARGET_ARCH_ARM) && !defined(__arm__) || \
     defined(V8_TARGET_ARCH_MIPS) && !defined(__mips__)
diff --git a/deps/v8/src/objects-inl.h b/deps/v8/src/objects-inl.h
index 8796865..af58572 100644
--- a/deps/v8/src/objects-inl.h
+++ b/deps/v8/src/objects-inl.h
@@ -4237,11 +4237,13 @@ uint32_t String::Hash() {
 
 StringHasher::StringHasher(int length)
   : length_(length),
-    raw_running_hash_(0),
+    raw_running_hash_(ISOLATE->HasherSeed()),
     array_index_(0),
     is_array_index_(0 < length_ && length_ <= String::kMaxArrayIndexSize),
     is_first_char_(true),
-    is_valid_(true) { }
+    is_valid_(true) {
+  ASSERT(FLAG_randomize_string_hashes == (raw_running_hash_ != 0));
+}
 
 
 bool StringHasher::has_trivial_hash() {
diff --git a/deps/v8/src/objects.cc b/deps/v8/src/objects.cc
index 6085b4e..6f5f36d 100644
--- a/deps/v8/src/objects.cc
+++ b/deps/v8/src/objects.cc
@@ -10482,7 +10482,9 @@ class TwoCharHashTableKey : public HashTableKey {
   TwoCharHashTableKey(uint32_t c1, uint32_t c2)
     : c1_(c1), c2_(c2) {
     // Char 1.
-    uint32_t hash = c1 + (c1 << 10);
+    uint32_t hash = ISOLATE->HasherSeed();
+    hash += c1;
+    hash += hash << 10;
     hash ^= hash >> 6;
     // Char 2.
     hash += c2;
diff --git a/deps/v8/src/x64/code-stubs-x64.cc b/deps/v8/src/x64/code-stubs-x64.cc
index df4438b..1bba5e6 100644
--- a/deps/v8/src/x64/code-stubs-x64.cc
+++ b/deps/v8/src/x64/code-stubs-x64.cc
@@ -4609,10 +4609,20 @@ void StringHelper::GenerateHashInit(MacroAssembler* masm,
                                     Register hash,
                                     Register character,
                                     Register scratch) {
-  // hash = character + (character << 10);
-  __ movl(hash, character);
-  __ shll(hash, Immediate(10));
-  __ addl(hash, character);
+  int32_t seed = masm->isolate()->HasherSeed();
+  if (seed != 0) {
+    ASSERT(FLAG_randomize_string_hashes);
+    // hash = (seed + character) + ((seed + character) << 10);
+    __ leal(scratch, Operand(character, seed));
+    __ shll(scratch, Immediate(10));
+    __ leal(hash, Operand(hash, character, times_1, seed));
+  } else {
+    ASSERT(!FLAG_randomize_string_hashes);
+    // hash = character + (character << 10);
+    __ movl(hash, character);
+    __ shll(hash, Immediate(10));
+    __ addl(hash, character);
+  }
   // hash ^= hash >> 6;
   __ movl(scratch, hash);
   __ sarl(scratch, Immediate(6));
-- 
1.7.7.1.msysgit.0