sending a struct with MapViewOfFile and reading an unknown value - c++

Question

I am basically trying to cast or copy my struct to my other process section view but I keep getting an error
C2760: syntax error: unexpected token 'identifier', expected 'declaration'
This is what I am doing:
type RPM(UINT_PTR ReadAddress)
{
if (hDriver == INVALID_HANDLE_VALUE) {
return {};
}
DWORD64 Bytes;
KM_READ_REQUEST ReadRequest{};
type response{};
ReadRequest.ProcessId = PID;
ReadRequest.Address = ReadAddress;
ReadRequest.Size = sizeof(type);
ReadRequest.Output = &response;
The problem is here:
auto pBuf = (ReadRequest)MapViewOfFile(hMapFile, FILE_MAP_WRITE, 0, 0, 4096);
if (!pBuf)
{
printf("OpenFileMappingA(write) fail! Error: %u\n", GetLastError());
system("pause");
}
printf("MapViewOfFile(write) created ! \n");
I am having another problem trying to read an unknown value from my kernel driver. It basically reads memory and then changes that value to another thing based on what I am reading from if its int, float, etc..
PKM_READ_REQUEST ReadInput = (PKM_READ_REQUEST)SharedSection; // cast readRequest to our struct which is in SharedSection.
void* ReadOutput = ReadInput->Output;
Status = ReadKernelMemory(Process, ReadInput->Address, ReadOutput, ReadInput->Size);
I am trying to copy it to my shared section so I can read it from user mode, but idk how to cast it or what the value would be.
memcpy(SharedSection, &ReadOutput, sizeof(ReadOutput));
This is how I want to try to read it, but cast it as the same way because I don't want to read it as void, I want to read it as the value that was given from my kernel mode.
auto pBuf = MapViewOfFile(hMapFile, FILE_MAP_READ, 0, 0, 4096);
if (!pBuf)
{
printf("OpenFileMappingA(write) fail! Error: %u\n", GetLastError());
system("pause");
}
printf("MapViewOfFile(write) created ! \n");
BTW, I am using the un-documented function mmcopyvirtualmemory in my kernel driver.

Answer 1

1.
auto pBuf = (ReadRequest)MapViewOfFile(hMapFile, FILE_MAP_WRITE, 0, 0, 4096);
The ReadRequest is not a type but an object, If you want to write the file map address as the struct KM_READ_REQUEST, you should convert the return pointer to the type of PKM_READ_REQUEST, and also take the control of the size of file map:
auto pBuf = (PKM_READ_REQUEST)MapViewOfFile(hMapFile, FILE_MAP_WRITE, 0, 0, sizeof(KM_READ_REQUEST));
So that you can set the PID,Address,Size and Output for it.
2.
memcpy(SharedSection, &ReadOutput, sizeof(ReadOutput));
ReadOutput is already the address of output value, So you don't
need the operation &.
Sizeof(a pointer) is always equal to 4(in 32-bit) and 8(in
64-bit);
You'd better use a new variable to store copied values, Instead of overwriting previous data。
So
type new_var;
memcpy(&new_var, ReadOutput, sizeof(KM_READ_REQUEST));
EDIT: Answer your comments,
You can set a single Event to communicate between driver and UM.
App:
hDevice = CreateFile(Device);
hEvent = CreateEvent(...);
DeviceIoControl(hDevice, IOCTL_SET_EVENT, &hEvent,...);
WaitForSingleObject(hEvent, INFINITE);
Driver:
case IOCTL_SET_EVENT:
{
HANDLE hUserEvent = *(HANDLE *)pIrp->AssociatedIrp.SystemBuffer;
status = ObReferenceObjectByHandle(hUserEvent, EVENT_MODIFY_STATE,*ExEventObjectType, KernelMode, (PVOID*)&pDevExt->pEvent, NULL);
ObDereferenceObject(pDevExt->pEvent);
break;
}
Then set event:
KeSetEvent(pdx->pEvent,...);