[wasm] Always trap for memory accesses with offset=uint32_max.

src/compiler/wasm-compiler.cc

 // Copyright 2015 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.
 
 #include "src/compiler/wasm-compiler.h"
 
 #include <memory>
 
 #include "src/isolate-inl.h"
 
@@ skipping 2894 matching lines @@
   DCHECK(module_ && module_->instance);
   uint32_t size = module_->instance->mem_size;
   byte memsize = wasm::WasmOpcodes::MemSize(memtype);
 
   size_t effective_size;
   if (size <= offset || size < (static_cast<uint64_t>(offset) + memsize)) {
     // Two checks are needed in the case where the offset is statically
     // out of bounds; one check for the offset being in bounds, and the next for
     // the offset + index being out of bounds for code to be patched correctly
     // on relocation.
-    size_t effective_offset = offset + memsize - 1;
+
+    // Check for overflows.
+    if ((std::numeric_limits<uint32_t>::max() - memsize) + 1 < offset) {
+      // Always trap. Do not use TrapAlways because it does not create a valid
+      // graph here.
+      trap_->TrapIfEq32(wasm::kTrapMemOutOfBounds, jsgraph()->Int32Constant(0),
+                        0, position);
+      return;
+    }
+    size_t effective_offset =
+        (offset - 1) + memsize;  // == offset + memsize - 1

[titzer, 2016/11/08 15:16:32]

comment is probably unnecessary

+
     Node* cond = graph()->NewNode(jsgraph()->machine()->Uint32LessThan(),
                                   jsgraph()->IntPtrConstant(effective_offset),
                                   jsgraph()->RelocatableInt32Constant(
                                       static_cast<uint32_t>(size),
                                       RelocInfo::WASM_MEMORY_SIZE_REFERENCE));
     trap_->AddTrapIfFalse(wasm::kTrapMemOutOfBounds, cond, position);
     // For offset > effective size, this relies on check above to fail and
     // effective size can be negative, relies on wrap around.
     effective_size = size - offset - memsize + 1;
   } else {
@@ skipping 559 matching lines @@
                             function_->code_start_offset),
            compile_ms);
   }
 
   return code;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8