[WebAssembly] Check if the section order is correct

Summary:
This patch checks if the section order is correct when reading a wasm
object file in `WasmObjectFile` and converting YAML to wasm object in
yaml2wasm. (It is not possible to check when reading YAML because it is
handled exclusively by the YAML reader.)

This checks the ordering of all known sections (core sections + known
custom sections). This also adds section ID DataCount section that will
be scheduled to be added in near future.

Reviewers: sbc100

Subscribers: dschuff, mgorny, jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D54924

llvm-svn: 349221

include/llvm/BinaryFormat/Wasm.h

@@ -200,6 +200,7 @@ enum : unsigned {
   WASM_SEC_ELEM = 9,       // Elements section
   WASM_SEC_CODE = 10,      // Function bodies (code)
   WASM_SEC_DATA = 11,      // Data segments
+  WASM_SEC_DATACOUNT = 12, // Data segment count
   WASM_SEC_EVENT = 13      // Event declarations
 };
 

include/llvm/Object/Wasm.h

@@ -283,6 +283,49 @@ private:
   uint32_t EventSection = 0;
 };
 
+class WasmSectionOrderChecker {
+public:
+  // We define orders for all core wasm sections and known custom sections.
+  enum : int {
+    // Core sections
+    // The order of standard sections is precisely given by the spec.
+    WASM_SEC_ORDER_TYPE = 1,
+    WASM_SEC_ORDER_IMPORT = 2,
+    WASM_SEC_ORDER_FUNCTION = 3,
+    WASM_SEC_ORDER_TABLE = 4,
+    WASM_SEC_ORDER_MEMORY = 5,
+    WASM_SEC_ORDER_GLOBAL = 6,
+    WASM_SEC_ORDER_EVENT = 7,
+    WASM_SEC_ORDER_EXPORT = 8,
+    WASM_SEC_ORDER_START = 9,
+    WASM_SEC_ORDER_ELEM = 10,
+    WASM_SEC_ORDER_DATACOUNT = 11,
+    WASM_SEC_ORDER_CODE = 12,
+    WASM_SEC_ORDER_DATA = 13,
+
+    // Custom sections
+    // "dylink" should be the very first section in the module
+    WASM_SEC_ORDER_DYLINK = 0,
+    // "linking" section requires DATA section in order to validate data symbols
+    WASM_SEC_ORDER_LINKING = 100,
+    // Must come after "linking" section in order to validate reloc indexes.
+    WASM_SEC_ORDER_RELOC = 101,
+    // "name" section must appear after DATA. Comes after "linking" to allow
+    // symbol table to set default function name.
+    WASM_SEC_ORDER_NAME = 102,
+    // "producers" section must appear after "name" section.
+    WASM_SEC_ORDER_PRODUCERS = 103
+  };
+
+  bool isValidSectionOrder(unsigned ID, StringRef CustomSectionName = "");
+
+private:
+  int LastOrder = -1; // Lastly seen known section's order
+
+  // Returns -1 for unknown sections.
+  int getSectionOrder(unsigned ID, StringRef CustomSectionName = "");
+};
+
 } // end namespace object
 
 inline raw_ostream &operator<<(raw_ostream &OS, const object::WasmSymbol &Sym) {

lib/Object/WasmObjectFile.cpp

@@ -24,6 +24,7 @@
 #include "llvm/Support/Error.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/LEB128.h"
+#include "llvm/Support/ScopedPrinter.h"
 #include <algorithm>
 #include <cassert>
 #include <cstdint>
@@ -207,8 +208,8 @@ static wasm::WasmTable readTable(WasmObjectFile::ReadContext &Ctx) {
   return Table;
 }
 
-static Error readSection(WasmSection &Section,
-                         WasmObjectFile::ReadContext &Ctx) {
+static Error readSection(WasmSection &Section, WasmObjectFile::ReadContext &Ctx,
+                         WasmSectionOrderChecker &Checker) {
   Section.Offset = Ctx.Ptr - Ctx.Start;
   Section.Type = readUint8(Ctx);
   LLVM_DEBUG(dbgs() << "readSection type=" << Section.Type << "\n");
@@ -231,6 +232,13 @@ static Error readSection(WasmSection &Section,
     Ctx.Ptr += SectionNameSize;
     Size -= SectionNameSize;
   }
+
+  if (!Checker.isValidSectionOrder(Section.Type, Section.Name)) {
+    return make_error<StringError>("Out of order section type: " +
+                                       llvm::to_string(Section.Type),
+                                   object_error::parse_failed);
+  }
+
   Section.Content = ArrayRef<uint8_t>(Ctx.Ptr, Size);
   Ctx.Ptr += Size;
   return Error::success();
@@ -265,8 +273,9 @@ WasmObjectFile::WasmObjectFile(MemoryBufferRef Buffer, Error &Err)
   }
 
   WasmSection Sec;
+  WasmSectionOrderChecker Checker;
   while (Ctx.Ptr < Ctx.End) {
-    if ((Err = readSection(Sec, Ctx)))
+    if ((Err = readSection(Sec, Ctx, Checker)))
       return;
     if ((Err = parseSection(Sec)))
       return;
@@ -1433,3 +1442,58 @@ WasmObjectFile::getWasmRelocation(DataRefImpl Ref) const {
   assert(Ref.d.b < Sec.Relocations.size());
   return Sec.Relocations[Ref.d.b];
 }
+
+int WasmSectionOrderChecker::getSectionOrder(unsigned ID,
+                                             StringRef CustomSectionName) {
+  switch (ID) {
+  case wasm::WASM_SEC_CUSTOM:
+    return StringSwitch<unsigned>(CustomSectionName)
+        .Case("dylink", WASM_SEC_ORDER_DYLINK)
+        .Case("linking", WASM_SEC_ORDER_LINKING)
+        .StartsWith("reloc.", WASM_SEC_ORDER_RELOC)
+        .Case("name", WASM_SEC_ORDER_NAME)
+        .Case("producers", WASM_SEC_ORDER_PRODUCERS)
+        .Default(-1);
+  case wasm::WASM_SEC_TYPE:
+    return WASM_SEC_ORDER_TYPE;
+  case wasm::WASM_SEC_IMPORT:
+    return WASM_SEC_ORDER_IMPORT;
+  case wasm::WASM_SEC_FUNCTION:
+    return WASM_SEC_ORDER_FUNCTION;
+  case wasm::WASM_SEC_TABLE:
+    return WASM_SEC_ORDER_TABLE;
+  case wasm::WASM_SEC_MEMORY:
+    return WASM_SEC_ORDER_MEMORY;
+  case wasm::WASM_SEC_GLOBAL:
+    return WASM_SEC_ORDER_GLOBAL;
+  case wasm::WASM_SEC_EXPORT:
+    return WASM_SEC_ORDER_EXPORT;
+  case wasm::WASM_SEC_START:
+    return WASM_SEC_ORDER_START;
+  case wasm::WASM_SEC_ELEM:
+    return WASM_SEC_ORDER_ELEM;
+  case wasm::WASM_SEC_CODE:
+    return WASM_SEC_ORDER_CODE;
+  case wasm::WASM_SEC_DATA:
+    return WASM_SEC_ORDER_DATA;
+  case wasm::WASM_SEC_DATACOUNT:
+    return WASM_SEC_ORDER_DATACOUNT;
+  case wasm::WASM_SEC_EVENT:
+    return WASM_SEC_ORDER_EVENT;
+  default:
+    llvm_unreachable("invalid section");
+  }
+}
+
+bool WasmSectionOrderChecker::isValidSectionOrder(unsigned ID,
+                                                  StringRef CustomSectionName) {
+  int Order = getSectionOrder(ID, CustomSectionName);
+  if (Order == -1) // Skip unknown sections
+    return true;
+  // There can be multiple "reloc." sections. Otherwise there shouldn't be any
+  // duplicate section orders.
+  bool IsValid = (LastOrder == Order && Order == WASM_SEC_ORDER_RELOC) ||
+                 LastOrder < Order;
+  LastOrder = Order;
+  return IsValid;
+}

test/Object/wasm-invalid-section-order.test

@@ -0,0 +1,16 @@
+# RUN: not obj2yaml %p/Inputs/WASM/invalid-section-order.wasm 2>&1 | FileCheck %s
+# CHECK: {{.*}}: Out of order section type: 10
+
+# Inputs/WASM/invalid-section-order.wasm is generated from this ll file, by
+# modifying WasmObjectWriter to incorrectly write the data section before the
+# code section.
+#
+# target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+# target triple = "wasm32-unknown-unknown"
+#
+# @data = global i32 0, align 4
+#
+# define void @foo() {
+# entry:
+#   ret void
+# }

test/ObjectYAML/wasm/invalid_section_order.yaml

@@ -0,0 +1,20 @@
+# RUN: not yaml2obj %s -o /dev/null 2>&1 | FileCheck %s
+
+--- !WASM
+FileHeader:
+  Version:         0x00000001
+Sections:
+  - Type:            TYPE
+    Signatures:
+      - Index:           0
+        ReturnType:      NORESULT
+        ParamTypes:      []
+  - Type:            CODE
+    Functions:
+      - Index:           0
+        Locals:          []
+        Body:            0B
+  # CHECK: Out of order section type: 3
+  - Type:            FUNCTION
+    FunctionTypes:   [ 0 ]
+...

tools/yaml2obj/yaml2wasm.cpp

@@ -13,6 +13,7 @@
 //===----------------------------------------------------------------------===//
 //
 
+#include "llvm/Object/Wasm.h"
 #include "llvm/ObjectYAML/ObjectYAML.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/LEB128.h"
@@ -516,7 +517,15 @@ int WasmWriter::writeWasm(raw_ostream &OS) {
   writeUint32(OS, Obj.Header.Version);
 
   // Write each section
+  llvm::object::WasmSectionOrderChecker Checker;
   for (const std::unique_ptr<WasmYAML::Section> &Sec : Obj.Sections) {
+    StringRef SecName = "";
+    if (auto S = dyn_cast<WasmYAML::CustomSection>(Sec.get()))
+      SecName = S->Name;
+    if (!Checker.isValidSectionOrder(Sec->Type, SecName)) {
+      errs() << "Out of order section type: " << Sec->Type << "\n";
+      return 1;
+    }
     encodeULEB128(Sec->Type, OS);
     std::string OutString;
     raw_string_ostream StringStream(OutString);