#ifndef _NTEXAPI_H
#if (PHNT_MODE != PHNT_MODE_KERNEL)

//
// Firmware environment values
//

/**
 * Retrieves the value of the specified firmware environment variable.
 * The user account that the app is running under must have the SE_SYSTEM_ENVIRONMENT_NAME privilege.
 *
 * @param VariableName The name of the firmware environment variable. The pointer must not be NULL.
 * @param VariableValue A pointer to a buffer that receives the value of the specified firmware environment variable.
 * @param ValueLength The size of the \c VariableValue buffer, in bytes.
 * @param ReturnLength If the function succeeds, the return length is the number of bytes stored in the \c VariableValue buffer.
 * @return NTSTATUS Successful or errant status.
 */
NTSYSCALLAPI
NTSTATUS
NTAPI
NtQuerySystemEnvironmentValue(
    _In_ PUNICODE_STRING VariableName,
    _Out_writes_bytes_(ValueLength) PWSTR VariableValue,
    _In_ USHORT ValueLength,
    _Out_opt_ PUSHORT ReturnLength
    );

#endif
#endif
View code on GitHub

#ifndef _NTZWAPI_H

NTSYSCALLAPI
NTSTATUS
NTAPI
ZwQuerySystemEnvironmentValue(
    _In_ PUNICODE_STRING VariableName,
    _Out_writes_bytes_(ValueLength) PWSTR VariableValue,
    _In_ USHORT ValueLength,
    _Out_opt_ PUSHORT ReturnLength
    );

#endif
View code on GitHub