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Commit b219d80f authored by Steven Moreland's avatar Steven Moreland
Browse files

Binder interface tokens: remove extra mallocs 

- writeInterfaceToken/enforceInterfaceToken try to get the interface
  token with GetStringRegion, so for classes with short enough
  interface descriptors, the string is allocated on the stack. A size
  of 64 was chosen since the longest interface descriptor in a
  frameworks/base AIDL file is ~40 characters.
- remove extra creation of String16 for writeInterfaceToken

Bug: 169674485
Test: atest aidl_integration_test
Change-Id: I78092abaa4df758ab699fcb103aa619b0b426e6c
parent 1f125fcd

core/jni/android_os_Parcel.cpp

+60 −33
Original line number Diff line number Diff line
@@ -638,36 +638,64 @@ static jboolean android_os_Parcel_hasFileDescriptors(jlong nativePtr) 
    return ret;

}



// String tries to allocate itself on the stack, within a known size, but will

// make a heap allocation if not.

template <size_t StackReserve>

class StackString {

public:

    StackString(JNIEnv* env, jstring str) : mEnv(env), mJStr(str) {

        LOG_ALWAYS_FATAL_IF(str == nullptr);

        mSize = env->GetStringLength(str);

        if (mSize > StackReserve) {

            mStr = new jchar[mSize];

        } else {

            mStr = &mBuffer[0];

        }

        mEnv->GetStringRegion(str, 0, mSize, mStr);

    }

    ~StackString() {

        if (mStr != &mBuffer[0]) {

            delete[] mStr;

        }

    }

    const jchar* str() { return mStr; }

    jsize size() { return mSize; }



private:

    JNIEnv* mEnv;

    jstring mJStr;



    jchar mBuffer[StackReserve];

    // pointer to &mBuffer[0] if string fits in mBuffer, otherwise owned

    jchar* mStr;

    jsize mSize;

};



// This size is chosen to be longer than most interface descriptors.

// Ones longer than this will be allocated on the heap.

typedef StackString<64> InterfaceDescriptorString;



static void android_os_Parcel_writeInterfaceToken(JNIEnv* env, jclass clazz, jlong nativePtr,

                                                  jstring name)

{

    Parcel* parcel = reinterpret_cast<Parcel*>(nativePtr);

    if (parcel != NULL) {

        // In the current implementation, the token is just the serialized interface name that

        // the caller expects to be invoking

        const jchar* str = env->GetStringCritical(name, 0);

        if (str != NULL) {

            parcel->writeInterfaceToken(String16(

                  reinterpret_cast<const char16_t*>(str),

                  env->GetStringLength(name)));

            env->ReleaseStringCritical(name, str);

        }

    if (parcel != nullptr) {

        InterfaceDescriptorString descriptor(env, name);

        parcel->writeInterfaceToken(reinterpret_cast<const char16_t*>(descriptor.str()),

                                    descriptor.size());

    }

}



static void android_os_Parcel_enforceInterface(JNIEnv* env, jclass clazz, jlong nativePtr, jstring name)

{

    Parcel* parcel = reinterpret_cast<Parcel*>(nativePtr);

    if (parcel != NULL) {

        const jchar* str = env->GetStringCritical(name, 0);

        if (str) {

    if (parcel != nullptr) {

        InterfaceDescriptorString descriptor(env, name);

        IPCThreadState* threadState = IPCThreadState::self();

        const int32_t oldPolicy = threadState->getStrictModePolicy();

            const bool isValid = parcel->enforceInterface(

                reinterpret_cast<const char16_t*>(str),

                env->GetStringLength(name),

                threadState);

            env->ReleaseStringCritical(name, str);

        const bool isValid =

                parcel->enforceInterface(reinterpret_cast<const char16_t*>(descriptor.str()),

                                         descriptor.size(), threadState);

        if (isValid) {

            const int32_t newPolicy = threadState->getStrictModePolicy();

            if (oldPolicy != newPolicy) {
@@ -683,7 +711,6 @@ static void android_os_Parcel_enforceInterface(JNIEnv* env, jclass clazz, jlong 
            return; // everything was correct -> return silently

        }

    }

    }



    // all error conditions wind up here

    jniThrowException(env, "java/lang/SecurityException",