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vm: make ContextifyContext a BaseObject
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Instead of adding a reference to the ContextifyContext by using
a v8::External, we make ContextifyContext a weak BaseObject that
whose wrapper is referenced by the sandbox via a private symbol.
This makes it easier to snapshot the contexts, in addition to
reusing the BaseObject lifetime management for ContextifyContexts.

PR-URL: #44796
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
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@joyeecheung
joyeecheung committed Oct 4, 2022
1 parent b3531bf commit 5b1bcf8
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Showing 4 changed files with 134 additions and 100 deletions.
3 changes: 1 addition & 2 deletions src/env.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -451,8 +451,7 @@ void IsolateData::CreateProperties() {
templ->Inherit(BaseObject::GetConstructorTemplate(this));
set_binding_data_ctor_template(templ);

set_contextify_global_template(
contextify::ContextifyContext::CreateGlobalTemplate(isolate_));
contextify::ContextifyContext::InitializeGlobalTemplates(this);
}

IsolateData::IsolateData(Isolate* isolate,
Expand Down
1 change: 1 addition & 0 deletions src/env_properties.h
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Original file line number Diff line number Diff line change
Expand Up @@ -332,6 +332,7 @@
V(blob_constructor_template, v8::FunctionTemplate) \
V(blocklist_constructor_template, v8::FunctionTemplate) \
V(contextify_global_template, v8::ObjectTemplate) \
V(contextify_wrapper_template, v8::ObjectTemplate) \
V(compiled_fn_entry_template, v8::ObjectTemplate) \
V(dir_instance_template, v8::ObjectTemplate) \
V(fd_constructor_template, v8::ObjectTemplate) \
Expand Down
197 changes: 113 additions & 84 deletions src/node_contextify.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -42,7 +42,6 @@ using v8::ArrayBufferView;
using v8::Boolean;
using v8::Context;
using v8::EscapableHandleScope;
using v8::External;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
Expand Down Expand Up @@ -108,62 +107,77 @@ Local<Name> Uint32ToName(Local<Context> context, uint32_t index) {

} // anonymous namespace

ContextifyContext::ContextifyContext(
BaseObjectPtr<ContextifyContext> ContextifyContext::New(
Environment* env,
Local<Object> sandbox_obj,
const ContextOptions& options)
: env_(env),
microtask_queue_wrap_(options.microtask_queue_wrap) {
const ContextOptions& options) {
HandleScope scope(env->isolate());
InitializeGlobalTemplates(env->isolate_data());
Local<ObjectTemplate> object_template = env->contextify_global_template();
if (object_template.IsEmpty()) {
object_template = CreateGlobalTemplate(env->isolate());
env->set_contextify_global_template(object_template);
}
DCHECK(!object_template.IsEmpty());
bool use_node_snapshot = per_process::cli_options->node_snapshot;
const SnapshotData* snapshot_data =
use_node_snapshot ? SnapshotBuilder::GetEmbeddedSnapshotData() : nullptr;

MicrotaskQueue* queue =
microtask_queue()
? microtask_queue().get()
options.microtask_queue_wrap
? options.microtask_queue_wrap->microtask_queue().get()
: env->isolate()->GetCurrentContext()->GetMicrotaskQueue();

Local<Context> v8_context;
if (!(CreateV8Context(env->isolate(), object_template, snapshot_data, queue)
.ToLocal(&v8_context)) ||
!InitializeContext(v8_context, env, sandbox_obj, options)) {
.ToLocal(&v8_context))) {
// Allocation failure, maximum call stack size reached, termination, etc.
return;
return BaseObjectPtr<ContextifyContext>();
}
return New(v8_context, env, sandbox_obj, options);
}

context_.Reset(env->isolate(), v8_context);
context_.SetWeak(this, WeakCallback, WeakCallbackType::kParameter);
env->AddCleanupHook(CleanupHook, this);
void ContextifyContext::MemoryInfo(MemoryTracker* tracker) const {
if (microtask_queue_wrap_) {
tracker->TrackField("microtask_queue_wrap",
microtask_queue_wrap_->object());
}
}

ContextifyContext::ContextifyContext(Environment* env,
Local<Object> wrapper,
Local<Context> v8_context,
const ContextOptions& options)
: BaseObject(env, wrapper),
microtask_queue_wrap_(options.microtask_queue_wrap) {
context_.Reset(env->isolate(), v8_context);
// This should only be done after the initial initializations of the context
// global object is finished.
DCHECK_NULL(v8_context->GetAlignedPointerFromEmbedderData(
ContextEmbedderIndex::kContextifyContext));
v8_context->SetAlignedPointerInEmbedderData(
ContextEmbedderIndex::kContextifyContext, this);
// It's okay to make this reference weak - V8 would create an internal
// reference to this context via the constructor of the wrapper.
// As long as the wrapper is alive, it's constructor is alive, and so
// is the context.
context_.SetWeak();
}

ContextifyContext::~ContextifyContext() {
env()->RemoveCleanupHook(CleanupHook, this);
Isolate* isolate = env()->isolate();
HandleScope scope(isolate);

env()->async_hooks()
->RemoveContext(PersistentToLocal::Weak(isolate, context_));
context_.Reset();
}


void ContextifyContext::CleanupHook(void* arg) {
ContextifyContext* self = static_cast<ContextifyContext*>(arg);
self->context_.Reset();
delete self;
}

Local<ObjectTemplate> ContextifyContext::CreateGlobalTemplate(
Isolate* isolate) {
Local<FunctionTemplate> function_template = FunctionTemplate::New(isolate);

Local<ObjectTemplate> object_template =
function_template->InstanceTemplate();
void ContextifyContext::InitializeGlobalTemplates(IsolateData* isolate_data) {
if (!isolate_data->contextify_global_template().IsEmpty()) {
return;
}
DCHECK(isolate_data->contextify_wrapper_template().IsEmpty());
Local<FunctionTemplate> global_func_template =
FunctionTemplate::New(isolate_data->isolate());
Local<ObjectTemplate> global_object_template =
global_func_template->InstanceTemplate();

NamedPropertyHandlerConfiguration config(
PropertyGetterCallback,
Expand All @@ -185,10 +199,15 @@ Local<ObjectTemplate> ContextifyContext::CreateGlobalTemplate(
{},
PropertyHandlerFlags::kHasNoSideEffect);

object_template->SetHandler(config);
object_template->SetHandler(indexed_config);
global_object_template->SetHandler(config);
global_object_template->SetHandler(indexed_config);
isolate_data->set_contextify_global_template(global_object_template);

return object_template;
Local<FunctionTemplate> wrapper_func_template =
BaseObject::MakeLazilyInitializedJSTemplate(isolate_data);
Local<ObjectTemplate> wrapper_object_template =
wrapper_func_template->InstanceTemplate();
isolate_data->set_contextify_wrapper_template(wrapper_object_template);
}

MaybeLocal<Context> ContextifyContext::CreateV8Context(
Expand Down Expand Up @@ -218,43 +237,45 @@ MaybeLocal<Context> ContextifyContext::CreateV8Context(
.ToLocal(&ctx)) {
return MaybeLocal<Context>();
}

return scope.Escape(ctx);
}

bool ContextifyContext::InitializeContext(Local<Context> ctx,
Environment* env,
Local<Object> sandbox_obj,
const ContextOptions& options) {
BaseObjectPtr<ContextifyContext> ContextifyContext::New(
Local<Context> v8_context,
Environment* env,
Local<Object> sandbox_obj,
const ContextOptions& options) {
HandleScope scope(env->isolate());

// This only initializes part of the context. The primordials are
// only initilaized when needed because even deserializing them slows
// things down significantly and they are only needed in rare occasions
// in the vm contexts.
if (InitializeContextRuntime(ctx).IsNothing()) {
return false;
if (InitializeContextRuntime(v8_context).IsNothing()) {
return BaseObjectPtr<ContextifyContext>();
}

Local<Context> main_context = env->context();
ctx->SetSecurityToken(main_context->GetSecurityToken());
Local<Object> new_context_global = v8_context->Global();
v8_context->SetSecurityToken(main_context->GetSecurityToken());

// We need to tie the lifetime of the sandbox object with the lifetime of
// newly created context. We do this by making them hold references to each
// other. The context can directly hold a reference to the sandbox as an
// embedder data field. However, we cannot hold a reference to a v8::Context
// directly in an Object, we instead hold onto the new context's global
// object instead (which then has a reference to the context).
ctx->SetEmbedderData(ContextEmbedderIndex::kSandboxObject, sandbox_obj);
sandbox_obj->SetPrivate(
main_context, env->contextify_global_private_symbol(), ctx->Global());
// embedder data field. The sandbox uses a private symbol to hold a reference
// to the ContextifyContext wrapper which in turn internally references
// the context from its constructor.
v8_context->SetEmbedderData(ContextEmbedderIndex::kSandboxObject,
sandbox_obj);

// Delegate the code generation validation to
// node::ModifyCodeGenerationFromStrings.
ctx->AllowCodeGenerationFromStrings(false);
ctx->SetEmbedderData(ContextEmbedderIndex::kAllowCodeGenerationFromStrings,
options.allow_code_gen_strings);
ctx->SetEmbedderData(ContextEmbedderIndex::kAllowWasmCodeGeneration,
options.allow_code_gen_wasm);
v8_context->AllowCodeGenerationFromStrings(false);
v8_context->SetEmbedderData(
ContextEmbedderIndex::kAllowCodeGenerationFromStrings,
options.allow_code_gen_strings);
v8_context->SetEmbedderData(ContextEmbedderIndex::kAllowWasmCodeGeneration,
options.allow_code_gen_wasm);

Utf8Value name_val(env->isolate(), options.name);
ContextInfo info(*name_val);
Expand All @@ -263,28 +284,43 @@ bool ContextifyContext::InitializeContext(Local<Context> ctx,
info.origin = *origin_val;
}

BaseObjectPtr<ContextifyContext> result;
Local<Object> wrapper;
{
Context::Scope context_scope(ctx);
Context::Scope context_scope(v8_context);
Local<String> ctor_name = sandbox_obj->GetConstructorName();
if (!ctor_name->Equals(ctx, env->object_string()).FromMaybe(false) &&
ctx->Global()
if (!ctor_name->Equals(v8_context, env->object_string()).FromMaybe(false) &&
new_context_global
->DefineOwnProperty(
ctx,
v8_context,
v8::Symbol::GetToStringTag(env->isolate()),
ctor_name,
static_cast<v8::PropertyAttribute>(v8::DontEnum))
.IsNothing()) {
return false;
return BaseObjectPtr<ContextifyContext>();
}
env->AssignToContext(v8_context, nullptr, info);

if (!env->contextify_wrapper_template()
->NewInstance(v8_context)
.ToLocal(&wrapper)) {
return BaseObjectPtr<ContextifyContext>();
}

result =
MakeBaseObject<ContextifyContext>(env, wrapper, v8_context, options);
// The only strong reference to the wrapper will come from the sandbox.
result->MakeWeak();
}

env->AssignToContext(ctx, nullptr, info);
if (sandbox_obj
->SetPrivate(
v8_context, env->contextify_context_private_symbol(), wrapper)
.IsNothing()) {
return BaseObjectPtr<ContextifyContext>();
}

// This should only be done after the initial initializations of the context
// global object is finished.
ctx->SetAlignedPointerInEmbedderData(ContextEmbedderIndex::kContextifyContext,
this);
return true;
return result;
}

void ContextifyContext::Init(Environment* env, Local<Object> target) {
Expand Down Expand Up @@ -350,22 +386,14 @@ void ContextifyContext::MakeContext(const FunctionCallbackInfo<Value>& args) {
}

TryCatchScope try_catch(env);
std::unique_ptr<ContextifyContext> context_ptr =
std::make_unique<ContextifyContext>(env, sandbox, options);
BaseObjectPtr<ContextifyContext> context_ptr =
ContextifyContext::New(env, sandbox, options);

if (try_catch.HasCaught()) {
if (!try_catch.HasTerminated())
try_catch.ReThrow();
return;
}

Local<Context> new_context = context_ptr->context();
if (new_context.IsEmpty()) return;

sandbox->SetPrivate(
env->context(),
env->contextify_context_private_symbol(),
External::New(env->isolate(), context_ptr.release()));
}


Expand All @@ -392,23 +420,24 @@ void ContextifyContext::WeakCallback(
ContextifyContext* ContextifyContext::ContextFromContextifiedSandbox(
Environment* env,
const Local<Object>& sandbox) {
MaybeLocal<Value> maybe_value =
sandbox->GetPrivate(env->context(),
env->contextify_context_private_symbol());
Local<Value> context_external_v;
if (maybe_value.ToLocal(&context_external_v) &&
context_external_v->IsExternal()) {
Local<External> context_external = context_external_v.As<External>();
return static_cast<ContextifyContext*>(context_external->Value());
Local<Value> context_global;
if (sandbox
->GetPrivate(env->context(), env->contextify_context_private_symbol())
.ToLocal(&context_global) &&
context_global->IsObject()) {
return Unwrap<ContextifyContext>(context_global.As<Object>());
}
return nullptr;
}

// static
template <typename T>
ContextifyContext* ContextifyContext::Get(const PropertyCallbackInfo<T>& args) {
return Get(args.This());
}

ContextifyContext* ContextifyContext::Get(Local<Object> object) {
Local<Context> context;
if (!args.This()->GetCreationContext().ToLocal(&context)) {
if (!object->GetCreationContext().ToLocal(&context)) {
return nullptr;
}
if (!ContextEmbedderTag::IsNodeContext(context)) {
Expand Down
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