Implement --check-stack-overflow flag for wasm-emscripten-finalize

scripts/test/lld.py

@@ -22,10 +22,12 @@
 
 
 def args_for_finalize(filename):
-   if 'shared' in filename:
-     return ['--side-module']
-   else:
-     return ['--global-base=568']
+  if 'safe_stack' in filename:
+    return ['--check-stack-overflow', '--global-base=568']
+  elif 'shared' in filename:
+    return ['--side-module']
+  else:
+    return ['--global-base=568']
 
 
 def test_wasm_emscripten_finalize():

src/tools/wasm-emscripten-finalize.cpp

@@ -48,6 +48,7 @@ int main(int argc, const char* argv[]) {
   bool debugInfo = false;
   bool isSideModule = false;
   bool legalizeJavaScriptFFI = true;
+  bool checkStackOverflow = false;
   uint64_t globalBase = INVALID_BASE;
   ToolOptions options("wasm-emscripten-finalize",
                       "Performs Emscripten-specific transforms on .wasm files");
@@ -127,6 +128,13 @@ int main(int argc, const char* argv[]) {
          [&dataSegmentFile](Options* o, const std::string& argument) {
            dataSegmentFile = argument;
          })
+    .add("--check-stack-overflow",
+         "",
+         "Check for stack overflows every time the stack is extended",
+         Options::Arguments::Zero,
+         [&checkStackOverflow](Options* o, const std::string&) {
+           checkStackOverflow = true;
+         })
     .add_positional("INFILE",
                     Options::Arguments::One,
                     [&infile](Options* o, const std::string& argument) {
@@ -200,6 +208,10 @@ int main(int argc, const char* argv[]) {
   }
   wasm.updateMaps();
 
+  if (checkStackOverflow && !isSideModule) {
+    generator.enforceStackLimit();
+  }
+
   if (isSideModule) {
     generator.replaceStackPointerGlobal();
     generator.generatePostInstantiateFunction();

src/wasm-emscripten.h

@@ -54,6 +54,8 @@ class EmscriptenGlueGenerator {
 
   void fixInvokeFunctionNames();
 
+  void enforceStackLimit();
+
   // Emits the data segments to a file. The file contains data from address base
   // onwards (we must pass in base, as we can't tell it from the wasm - the
   // first segment may start after a run of zeros, but we need those zeros in
@@ -71,11 +73,13 @@ class EmscriptenGlueGenerator {
 
   Global* getStackPointerGlobal();
   Expression* generateLoadStackPointer();
-  Expression* generateStoreStackPointer(Expression* value);
+  Expression* generateStoreStackPointer(Function* func, Expression* value);
   void generateDynCallThunk(std::string sig);
   void generateStackSaveFunction();
   void generateStackAllocFunction();
   void generateStackRestoreFunction();
+  void generateSetStackLimitFunction();
+  Name importStackOverflowHandler();
 };
 
 } // namespace wasm

src/wasm/wasm-emscripten.cpp

@@ -37,8 +37,11 @@ static Name STACK_SAVE("stackSave");
 static Name STACK_RESTORE("stackRestore");
 static Name STACK_ALLOC("stackAlloc");
 static Name STACK_INIT("stack$init");
+static Name STACK_LIMIT("__stack_limit");
+static Name SET_STACK_LIMIT("__set_stack_limit");
 static Name POST_INSTANTIATE("__post_instantiate");
 static Name ASSIGN_GOT_ENTIRES("__assign_got_enties");
+static Name STACK_OVERFLOW_IMPORT("__handle_stack_overflow");
 
 void addExportedFunction(Module& wasm, Function* function) {
   wasm.addFunction(function);
@@ -92,8 +95,32 @@ Expression* EmscriptenGlueGenerator::generateLoadStackPointer() {
   return builder.makeGlobalGet(stackPointer->name, i32);
 }
 
+inline Expression* stackBoundsCheck(Builder& builder,
+                                    Function* func,
+                                    Expression* value,
+                                    Global* stackPointer,
+                                    Global* stackLimit,
+                                    Name handler) {
+  // Add a local to store the value of the expression. We need the value twice:
+  // once to check if it has overflowed, and again to assign to store it.
+  auto newSP = Builder::addVar(func, stackPointer->type);
+  // (if (i32.lt_u (local.tee $newSP (...value...)) (global.get $__stack_limit))
+  //  (call $handler))
+  auto check =
+    builder.makeIf(builder.makeBinary(
+                     BinaryOp::LtUInt32,
+                     builder.makeLocalTee(newSP, value),
+                     builder.makeGlobalGet(stackLimit->name, stackLimit->type)),
+                   builder.makeCall(handler, {}, none));
+  // (global.set $__stack_pointer (local.get $newSP))
+  auto newSet = builder.makeGlobalSet(
+    stackPointer->name, builder.makeLocalGet(newSP, stackPointer->type));
+  return builder.blockify(check, newSet);
+}
+
 Expression*
-EmscriptenGlueGenerator::generateStoreStackPointer(Expression* value) {
+EmscriptenGlueGenerator::generateStoreStackPointer(Function* func,
+                                                   Expression* value) {
   if (!useStackPointerGlobal) {
     return builder.makeStore(
       /* bytes  =*/4,
@@ -107,6 +134,14 @@ EmscriptenGlueGenerator::generateStoreStackPointer(Expression* value) {
   if (!stackPointer) {
     Fatal() << "stack pointer global not found";
   }
+  if (auto* stackLimit = wasm.getGlobalOrNull(STACK_LIMIT)) {
+    return stackBoundsCheck(builder,
+                            func,
+                            value,
+                            stackPointer,
+                            stackLimit,
+                            importStackOverflowHandler());
+  }
   return builder.makeGlobalSet(stackPointer->name, value);
 }
 
@@ -132,7 +167,7 @@ void EmscriptenGlueGenerator::generateStackAllocFunction() {
   Const* subConst = builder.makeConst(Literal(~bitMask));
   Binary* maskedSub = builder.makeBinary(AndInt32, sub, subConst);
   LocalSet* teeStackLocal = builder.makeLocalTee(1, maskedSub);
-  Expression* storeStack = generateStoreStackPointer(teeStackLocal);
+  Expression* storeStack = generateStoreStackPointer(function, teeStackLocal);
 
   Block* block = builder.makeBlock();
   block->list.push_back(storeStack);
@@ -149,7 +184,7 @@ void EmscriptenGlueGenerator::generateStackRestoreFunction() {
   Function* function =
     builder.makeFunction(STACK_RESTORE, std::move(params), none, {});
   LocalGet* getArg = builder.makeLocalGet(0, i32);
-  Expression* store = generateStoreStackPointer(getArg);
+  Expression* store = generateStoreStackPointer(function, getArg);
 
   function->body = store;
 
@@ -444,6 +479,86 @@ void EmscriptenGlueGenerator::replaceStackPointerGlobal() {
   wasm.removeGlobal(stackPointer->name);
 }
 
+struct StackLimitEnforcer : public WalkerPass<PostWalker<StackLimitEnforcer>> {
+  StackLimitEnforcer(Global* stackPointer,
+                     Global* stackLimit,
+                     Builder& builder,
+                     Name handler)
+    : stackPointer(stackPointer), stackLimit(stackLimit), builder(builder),
+      handler(handler) {}
+
+  bool isFunctionParallel() override { return true; }
+
+  Pass* create() override {
+    return new StackLimitEnforcer(stackPointer, stackLimit, builder, handler);
+  }
+
+  void visitGlobalSet(GlobalSet* curr) {
+    if (getModule()->getGlobalOrNull(curr->name) == stackPointer) {
+      replaceCurrent(stackBoundsCheck(builder,
+                                      getFunction(),
+                                      curr->value,
+                                      stackPointer,
+                                      stackLimit,
+                                      handler));
+    }
+  }
+
+private:
+  Global* stackPointer;
+  Global* stackLimit;
+  Builder& builder;
+  Name handler;
+};
+
+void EmscriptenGlueGenerator::enforceStackLimit() {
+  Global* stackPointer = getStackPointerGlobal();
+  if (!stackPointer) {
+    return;
+  }
+
+  auto* stackLimit = builder.makeGlobal(STACK_LIMIT,
+                                        stackPointer->type,
+                                        builder.makeConst(Literal(0)),
+                                        Builder::Mutable);
+  wasm.addGlobal(stackLimit);
+
+  auto handler = importStackOverflowHandler();
+
+  StackLimitEnforcer walker(stackPointer, stackLimit, builder, handler);
+  PassRunner runner(&wasm);
+  walker.run(&runner, &wasm);
+
+  generateSetStackLimitFunction();
+}
+
+void EmscriptenGlueGenerator::generateSetStackLimitFunction() {
+  Function* function =
+    builder.makeFunction(SET_STACK_LIMIT, std::vector<Type>({i32}), none, {});
+  LocalGet* getArg = builder.makeLocalGet(0, i32);
+  Expression* store = builder.makeGlobalSet(STACK_LIMIT, getArg);
+  function->body = store;
+  addExportedFunction(wasm, function);
+}
+
+Name EmscriptenGlueGenerator::importStackOverflowHandler() {
+  ImportInfo info(wasm);
+
+  if (auto* existing = info.getImportedFunction(ENV, STACK_OVERFLOW_IMPORT)) {
+    return existing->name;
+  } else {
+    auto* import = new Function;
+    import->name = STACK_OVERFLOW_IMPORT;
+    import->module = ENV;
+    import->base = STACK_OVERFLOW_IMPORT;
+    auto* functionType = ensureFunctionType("v", &wasm);
+    import->type = functionType->name;
+    FunctionTypeUtils::fillFunction(import, functionType);
+    wasm.addFunction(import);
+    return STACK_OVERFLOW_IMPORT;
+  }
+}
+
 const Address UNKNOWN_OFFSET(uint32_t(-1));
 
 std::vector<Address> getSegmentOffsets(Module& wasm) {

test/lld/recursive_safe_stack.wast

@@ -0,0 +1,90 @@
+(module
+ (type $0 (func (param i32 i32) (result i32)))
+ (type $1 (func))
+ (type $2 (func (result i32)))
+ (import "env" "printf" (func $printf (param i32 i32) (result i32)))
+ (memory $0 2)
+ (data (i32.const 568) "%d:%d\n\00Result: %d\n\00")
+ (table $0 1 1 funcref)
+ (global $global$0 (mut i32) (i32.const 66128))
+ (global $global$1 i32 (i32.const 66128))
+ (global $global$2 i32 (i32.const 587))
+ (export "memory" (memory $0))
+ (export "__wasm_call_ctors" (func $__wasm_call_ctors))
+ (export "__heap_base" (global $global$1))
+ (export "__data_end" (global $global$2))
+ (export "main" (func $main))
+ (func $__wasm_call_ctors (; 1 ;) (type $1)
+ )
+ (func $foo (; 2 ;) (type $0) (param $0 i32) (param $1 i32) (result i32)
+  (local $2 i32)
+  (global.set $global$0
+   (local.tee $2
+    (i32.sub
+     (global.get $global$0)
+     (i32.const 16)
+    )
+   )
+  )
+  (i32.store offset=4
+   (local.get $2)
+   (local.get $1)
+  )
+  (i32.store
+   (local.get $2)
+   (local.get $0)
+  )
+  (drop
+   (call $printf
+    (i32.const 568)
+    (local.get $2)
+   )
+  )
+  (global.set $global$0
+   (i32.add
+    (local.get $2)
+    (i32.const 16)
+   )
+  )
+  (i32.add
+   (local.get $1)
+   (local.get $0)
+  )
+ )
+ (func $__original_main (; 3 ;) (type $2) (result i32)
+  (local $0 i32)
+  (global.set $global$0
+   (local.tee $0
+    (i32.sub
+     (global.get $global$0)
+     (i32.const 16)
+    )
+   )
+  )
+  (i32.store
+   (local.get $0)
+   (call $foo
+    (i32.const 1)
+    (i32.const 2)
+   )
+  )
+  (drop
+   (call $printf
+    (i32.const 575)
+    (local.get $0)
+   )
+  )
+  (global.set $global$0
+   (i32.add
+    (local.get $0)
+    (i32.const 16)
+   )
+  )
+  (i32.const 0)
+ )
+ (func $main (; 4 ;) (type $0) (param $0 i32) (param $1 i32) (result i32)
+  (call $__original_main)
+ )
+ ;; custom section "producers", size 111
+)
+