Set rEFInd next boot default from Windows

rEFIndNextBoot.cpp

// (c) 2018 Taeyeon Mori
// CC0
//

#include "stdafx.h"
#include <Windows.h>

#define REFIND_GUID L"{36d08fa7-cf0b-42f5-8f14-68df73ed3740}"
#define PREVIOUS_BOOT L"PreviousBoot"


void wperror(const char *name)
{
	TCHAR buf[1024];
	DWORD err = GetLastError();
	DWORD len = FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, nullptr, err, 0, buf, 1024, nullptr);
	buf[len] = 0;
	printf("%s error (0x%lx): %ls\r\n", name, err, buf);
}

// See https://docs.microsoft.com/en-us/windows/desktop/SecAuthZ/enabling-and-disabling-privileges-in-c--
BOOL SetPrivilege(
	HANDLE hToken,          // access token handle
	LPCTSTR lpszPrivilege,  // name of privilege to enable/disable
	BOOL bEnablePrivilege   // to enable or disable privilege
)
{
	TOKEN_PRIVILEGES tp;
	LUID luid;

	if (!LookupPrivilegeValue(
		NULL,            // lookup privilege on local system
		lpszPrivilege,   // privilege to lookup 
		&luid))        // receives LUID of privilege
	{
		wperror("LookupPrivilegeValue");
		return FALSE;
	}

	tp.PrivilegeCount = 1;
	tp.Privileges[0].Luid = luid;
	if (bEnablePrivilege)
		tp.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;
	else
		tp.Privileges[0].Attributes = 0;

	// Enable the privilege or disable all privileges.

	if (!AdjustTokenPrivileges(
		hToken,
		FALSE,
		&tp,
		sizeof(TOKEN_PRIVILEGES),
		(PTOKEN_PRIVILEGES)NULL,
		(PDWORD)NULL))
	{
		wperror("AdjustTokenPrivileges");
		return FALSE;
	}

	if (GetLastError() == ERROR_NOT_ALL_ASSIGNED)

	{
		printf("The token does not have the specified privilege. \n");
		return FALSE;
	}

	return TRUE;
}


void synopsis()
{
	puts("Synopsis: rEFIndNextBoot.exe [entry]");
	puts("");
	puts("Set or get (when entry not given) the rEFInd PreviousBoot nvram variable");
}


int wmain(int argc, wchar_t **argv, wchar_t **envp)
{
	if (argc > 2)
	{
		puts("Error: too many arguments.");
		puts("");
		synopsis();
		return 5;
	}

	// Take privileges
	HANDLE at;
	if (!OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES, &at))
	{
		wperror("OpenProcessToken");
		return 40;
	}

	if (!SetPrivilege(at, SE_SYSTEM_ENVIRONMENT_NAME, true))
	{
		return 41;
	}
	
	// Set new value
	if (argc == 2)
	{
		if (!SetFirmwareEnvironmentVariable(PREVIOUS_BOOT, REFIND_GUID, argv[1], wcslen(argv[1]) * sizeof(wchar_t)))
		{
			wperror("SetFirmwareEnvironmentVariable");
			return 5;
		}
	}

	// Print current value
	wchar_t buf[1024];
	DWORD len = GetFirmwareEnvironmentVariable(PREVIOUS_BOOT, REFIND_GUID, buf, sizeof(buf));
	if (len > 0)
	{
		buf[len] = 0;
		printf("rEFInd PreviousBoot value (%d): %ls\r\n", len / sizeof(wchar_t), buf);
		return 0;
	}
	else
	{
		wperror("GetFirmwareEnvironmentVariable");
		return 3;
	}
}