[wasm] Validate the alignment of load and store instructions.

src/wasm/ast-decoder.h

 // 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.
 
 #ifndef V8_WASM_AST_DECODER_H_
 #define V8_WASM_AST_DECODER_H_
 
 #include "src/signature.h"
 #include "src/wasm/decoder.h"
 #include "src/wasm/wasm-opcodes.h"
@@ skipping 167 matching lines @@
   inline uint32_t read_entry(Decoder* decoder, unsigned i) {
     DCHECK(i <= table_count);
     return table ? decoder->read_u32(table + i * sizeof(uint32_t)) : 0;
   }
 };
 
 struct MemoryAccessOperand {
   uint32_t alignment;
   uint32_t offset;
   unsigned length;
-  inline MemoryAccessOperand(Decoder* decoder, const byte* pc) {
+  inline MemoryAccessOperand(Decoder* decoder, const byte* pc,
+                             uint32_t max_alignment) {
     unsigned alignment_length;
     alignment =
         decoder->checked_read_u32v(pc, 1, &alignment_length, "alignment");
+    if (max_alignment < alignment) {
+      decoder->error(pc,

[titzer, 2016/09/02 07:46:23]

How about printing the expected maximum and the actual value as part of the
error message? You have to pass the position in that case.

[ahaas, 2016/09/02 11:35:45]

Done.

+                     "alignment must be less or equal to natural alignment");
+    }
     unsigned offset_length;
     offset = decoder->checked_read_u32v(pc, 1 + alignment_length,
                                         &offset_length, "offset");
     length = alignment_length + offset_length;
   }
 };
 
 struct ReturnArityOperand {
   uint32_t arity;
   unsigned length;
@@ skipping 130 matching lines @@
   }
 
   bool has_next() { return pc_ < end_; }
 };
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_WASM_AST_DECODER_H_