ReBarState.cpp

#include <iostream>
#include <Windows.h>
#include <string>

#define VARIABLE_ATTRIBUTE_NON_VOLATILE 0x00000001
#define VARIABLE_ATTRIBUTE_BOOTSERVICE_ACCESS 0x00000002
#define VARIABLE_ATTRIBUTE_RUNTIME_ACCESS 0x00000004

BOOLEAN RaisePriviledge()
{
	DWORD len;
	HANDLE hTok;
	TOKEN_PRIVILEGES tokp;

	if (!OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY,
		&hTok)) {
		return FALSE;
	}

	LookupPrivilegeValue(NULL, SE_SYSTEM_ENVIRONMENT_NAME, &tokp.Privileges[0].Luid);
	tokp.PrivilegeCount = 1;
	tokp.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;

	AdjustTokenPrivileges(hTok, FALSE, &tokp, 0, NULL, &len);

	if (GetLastError() != ERROR_SUCCESS) {
		return FALSE;
	}
	return TRUE;
}

int main()
{
	std::string i;
	UINT8 rBarState;
	DWORD rSize;
	DWORD size = sizeof(UINT8);
	DWORD dwAttributes = VARIABLE_ATTRIBUTE_NON_VOLATILE | VARIABLE_ATTRIBUTE_BOOTSERVICE_ACCESS | VARIABLE_ATTRIBUTE_RUNTIME_ACCESS;

	const TCHAR name[] = TEXT("ReBarState");
	const TCHAR guid[] = TEXT("{A3C5B77A-C88F-4A93-BF1C-4A92A32C65CE}");

	if (!RaisePriviledge()) {
		std::cout << "Failed to obtain SE_SYSTEM_ENVIRONMENT_NAME. Try running as admin\n";
	}
	else {
		std::cout << "Obtained SE_SYSTEM_ENVIRONMENT_NAME\n";
	}

	rSize = GetFirmwareEnvironmentVariable(name, guid, &rBarState, 1);

	if (rSize) {
		std::cout << "Current ReBarState " << +rBarState << " len " << rSize << "\n";
	}

	std::cout << "\nVerify that 4G Decoding is enabled otherwise system will not POST with GPU. Also make sure you have suffecient MMIOH space for the GPU BAR size (test with Linux if you have AMD)\n";
	std::cout << "\nEnter ReBarState Value\n 0: disabled \n >0: maximum BAR size set to x^2 \n 32: Unlmited BAR size\n\n";

	std::getline(std::cin, i);

	rBarState = std::stoi(i);
	std::cout << "Recived value of " << +rBarState << ". Writing to ReBarState\n\n";


	if (SetFirmwareEnvironmentVariableEx(name, guid, &rBarState, size, dwAttributes) == TRUE) {
		std::cout << "Successfully wrote ReBarState UEFI variable\n";
	}
	else {
		std::cout << "Failed to write ReBarState UEFI variable\n";
	}
	std::cout << "You can close the app now\n";
	std::cin.get();

}