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

According to the WebAssembly specification the alignment of load and
store instructions has to be less or equal to natural alignment.

R=titzer@chromium.org

Review-Url: https://codereview.chromium.org/2285643002
Cr-Commit-Position: refs/heads/master@{#39131}

src/wasm/ast-decoder.cc

@@ -401,7 +401,7 @@ class WasmDecoder : public Decoder {
       FOREACH_STORE_MEM_OPCODE(DECLARE_OPCODE_CASE)
 #undef DECLARE_OPCODE_CASE
       {
-        MemoryAccessOperand operand(this, pc);
+        MemoryAccessOperand operand(this, pc, UINT32_MAX);
         return 1 + operand.length;
       }
       case kExprBr:
@@ -1378,7 +1378,9 @@ class WasmFullDecoder : public WasmDecoder {
   }
 
   int DecodeLoadMem(LocalType type, MachineType mem_type) {
-    MemoryAccessOperand operand(this, pc_);
+    MemoryAccessOperand operand(this, pc_,
+                                ElementSizeLog2Of(mem_type.representation()));
+
     Value index = Pop(0, kAstI32);
     TFNode* node = BUILD(LoadMem, type, mem_type, index.node, operand.offset,
                          operand.alignment, position());
@@ -1387,7 +1389,8 @@ class WasmFullDecoder : public WasmDecoder {
   }
 
   int DecodeStoreMem(LocalType type, MachineType mem_type) {
-    MemoryAccessOperand operand(this, pc_);
+    MemoryAccessOperand operand(this, pc_,
+                                ElementSizeLog2Of(mem_type.representation()));
     Value val = Pop(1, type);
     Value index = Pop(0, kAstI32);
     BUILD(StoreMem, mem_type, index.node, operand.offset, operand.alignment,

src/wasm/ast-decoder.h

@@ -185,10 +185,17 @@ 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, pc + 1,
+                     "invalid alignment; expected maximum alignment is %u, "
+                     "actual alignment is %u",
+                     max_alignment, alignment);
+    }
     unsigned offset_length;
     offset = decoder->checked_read_u32v(pc, 1 + alignment_length,
                                         &offset_length, "offset");

src/wasm/wasm-interpreter.cc

@@ -1444,7 +1444,7 @@ class ThreadImpl : public WasmInterpreter::Thread {
 
 #define LOAD_CASE(name, ctype, mtype)                                       \
   case kExpr##name: {                                                       \
-    MemoryAccessOperand operand(&decoder, code->at(pc));                    \
+    MemoryAccessOperand operand(&decoder, code->at(pc), sizeof(ctype));     \
     uint32_t index = Pop().to<uint32_t>();                                  \
     size_t effective_mem_size = instance()->mem_size - sizeof(mtype);       \
     if (operand.offset > effective_mem_size ||                              \
@@ -1476,7 +1476,7 @@ class ThreadImpl : public WasmInterpreter::Thread {
 
 #define STORE_CASE(name, ctype, mtype)                                        \
   case kExpr##name: {                                                         \
-    MemoryAccessOperand operand(&decoder, code->at(pc));                      \
+    MemoryAccessOperand operand(&decoder, code->at(pc), sizeof(ctype));       \
     WasmVal val = Pop();                                                      \
     uint32_t index = Pop().to<uint32_t>();                                    \
     size_t effective_mem_size = instance()->mem_size - sizeof(mtype);         \

test/unittests/wasm/ast-decoder-unittest.cc

@@ -1093,6 +1093,40 @@ TEST_F(AstDecoderTest, LoadMemOffset) {
   }
 }
 
+TEST_F(AstDecoderTest, LoadMemAlignment) {
+  struct {
+    WasmOpcode instruction;
+    uint32_t maximum_aligment;
+  } values[] = {
+      {kExprI32LoadMem8U, 0},   // --
+      {kExprI32LoadMem8S, 0},   // --
+      {kExprI32LoadMem16U, 1},  // --
+      {kExprI32LoadMem16S, 1},  // --
+      {kExprI64LoadMem8U, 0},   // --
+      {kExprI64LoadMem8S, 0},   // --
+      {kExprI64LoadMem16U, 1},  // --
+      {kExprI64LoadMem16S, 1},  // --
+      {kExprI64LoadMem32U, 2},  // --
+      {kExprI64LoadMem32S, 2},  // --
+      {kExprI32LoadMem, 2},     // --
+      {kExprI64LoadMem, 3},     // --
+      {kExprF32LoadMem, 2},     // --
+      {kExprF64LoadMem, 3},     // --
+  };
+
+  for (int i = 0; i < arraysize(values); i++) {
+    for (byte alignment = 0; alignment <= 4; alignment++) {
+      byte code[] = {kExprI8Const, 0, static_cast<byte>(values[i].instruction),
+                     alignment, ZERO_OFFSET};
+      if (static_cast<uint32_t>(alignment) <= values[i].maximum_aligment) {
+        EXPECT_VERIFIES(sigs.v_i(), code);
+      } else {
+        EXPECT_FAILURE(sigs.v_i(), code);
+      }
+    }
+  }
+}
+
 TEST_F(AstDecoderTest, StoreMemOffset) {
   for (int offset = 0; offset < 128; offset += 7) {
     byte code[] = {WASM_STORE_MEM_OFFSET(MachineType::Int32(), offset,