NtQuerySystemEnvironmentValueEx - NtDoc

#ifndef _NTEXAPI_H
#if (PHNT_MODE != PHNT_MODE_KERNEL)

/**
 * Retrieves the value of the specified firmware environment variable and its attributes.
 * 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 VendorGuid The GUID that represents the namespace of the firmware environment variable.
 * @param Buffer A pointer to a buffer that receives the value of the specified firmware environment variable.
 * @param BufferLength The size of the \c Buffer, in bytes.
 * @param Attributes Bitmask identifying UEFI variable attributes associated with the variable.
 * @return NTSTATUS Successful or errant status.
 */
NTSYSCALLAPI
NTSTATUS
NTAPI
NtQuerySystemEnvironmentValueEx(
    _In_ PUNICODE_STRING VariableName,
    _In_ PCGUID VendorGuid,
    _Out_writes_bytes_opt_(*BufferLength) PVOID Buffer,
    _Inout_ PULONG BufferLength,
    _Out_opt_ PULONG Attributes // EFI_VARIABLE_*
    );

#endif
#endif
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#ifndef _NTZWAPI_H

NTSYSCALLAPI
NTSTATUS
NTAPI
ZwQuerySystemEnvironmentValueEx(
    _In_ PUNICODE_STRING VariableName,
    _In_ PCGUID VendorGuid,
    _Out_writes_bytes_opt_(*BufferLength) PVOID Buffer,
    _Inout_ PULONG BufferLength,
    _Out_opt_ PULONG Attributes // EFI_VARIABLE_*
    );

#endif
View code on GitHub