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

src/wasm/ast-decoder.h

Index: src/wasm/ast-decoder.h
diff --git a/src/wasm/ast-decoder.h b/src/wasm/ast-decoder.h
index 22ae789c1b42dfd9c57bb81f519b0a08b6cf88fc..f653d1de6ff07c66237f179173868464cd9cf77e 100644
--- a/src/wasm/ast-decoder.h
+++ b/src/wasm/ast-decoder.h
@@ -185,10 +185,15 @@ 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");