[wasm] Avoid integer overflow on function locals check

On 32-bit systems, the computation {count + type_list->size()} can
overflow, leading to memory corruption later on.

R=titzer@chromium.org

Bug: chromium:819869
Change-Id: Ic81d201e58211e3989b4e945cd52e98dc951fbda
Reviewed-on: https://chromium-review.googlesource.com/955025
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51817}

src/wasm/baseline/liftoff-compiler.cc

@@ -41,6 +41,8 @@ class MovableLabel {
   Label* get() { return label_.get(); }
   MovableLabel() : MovableLabel(new Label()) {}
 
+  operator bool() const { return label_ != nullptr; }
+
   static MovableLabel None() { return MovableLabel(nullptr); }
 
  private:
@@ -53,6 +55,8 @@ class MovableLabel {
  public:
   Label* get() { return &label_; }
 
+  operator bool() const { return true; }
+
   static MovableLabel None() { return MovableLabel(); }
 
  private:
@@ -148,6 +152,8 @@ class LiftoffCompiler {
         codegen_zone_(codegen_zone),
         safepoint_table_builder_(compilation_zone_) {}
 
+  ~LiftoffCompiler() { BindUnboundLabels(nullptr); }
+
   bool ok() const { return ok_; }
 
   void unsupported(Decoder* decoder, const char* reason) {
@@ -185,7 +191,8 @@ class LiftoffCompiler {
 #ifdef DEBUG
     // Bind all labels now, otherwise their destructor will fire a DCHECK error
     // if they where referenced before.
-    for (uint32_t i = 0, e = decoder->control_depth(); i < e; ++i) {
+    uint32_t control_depth = decoder ? decoder->control_depth() : 0;
+    for (uint32_t i = 0; i < control_depth; ++i) {
       Control* c = decoder->control_at(i);
       Label* label = c->label.get();
       if (!label->is_bound()) __ bind(label);
@@ -258,7 +265,7 @@ class LiftoffCompiler {
         OutOfLineCode::StackCheck(position, __ cache_state()->used_registers));
     OutOfLineCode& ool = out_of_line_code_.back();
     __ StackCheck(ool.label.get());
-    __ bind(ool.continuation.get());
+    if (ool.continuation) __ bind(ool.continuation.get());
   }
 
   void StartFunctionBody(Decoder* decoder, Control* block) {

src/wasm/function-body-decoder-impl.h

@@ -682,7 +682,8 @@ class WasmDecoder : public Decoder {
       uint32_t count = decoder->consume_u32v("local count");
       if (decoder->failed()) return false;
 
-      if ((count + type_list->size()) > kV8MaxWasmFunctionLocals) {
+      DCHECK_LE(type_list->size(), kV8MaxWasmFunctionLocals);
+      if (count > kV8MaxWasmFunctionLocals - type_list->size()) {
         decoder->error(decoder->pc() - 1, "local count too large");
         return false;
       }

test/mjsunit/regress/wasm/regress-819869.js

@@ -0,0 +1,12 @@
+// Copyright 2018 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+load('test/mjsunit/wasm/wasm-constants.js');
+load('test/mjsunit/wasm/wasm-module-builder.js');
+
+var builder = new WasmModuleBuilder();
+builder.addFunction(undefined, kSig_i_i)
+    .addLocals({i32_count: 0xffffffff})
+    .addBody([]);
+assertThrows(() => builder.instantiate(), WebAssembly.CompileError);