NtCreateSectionEx - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTMMAPI_H
// Sections
#if (PHNT_MODE != PHNT_MODE_KERNEL)
#if (PHNT_VERSION >= PHNT_REDSTONE5)

NTSYSCALLAPI
NTSTATUS
NTAPI
NtCreateSectionEx(
    _Out_ PHANDLE SectionHandle,
    _In_ ACCESS_MASK DesiredAccess,
    _In_opt_ POBJECT_ATTRIBUTES ObjectAttributes,
    _In_opt_ PLARGE_INTEGER MaximumSize,
    _In_ ULONG SectionPageProtection,
    _In_ ULONG AllocationAttributes,
    _In_opt_ HANDLE FileHandle,
    _Inout_updates_opt_(ExtendedParameterCount) PMEM_EXTENDED_PARAMETER ExtendedParameters,
    _In_ ULONG ExtendedParameterCount
    );

#endif
#endif
#endif

View code on GitHub
#ifndef _NTZWAPI_H

NTSYSCALLAPI
NTSTATUS
NTAPI
ZwCreateSectionEx(
    _Out_ PHANDLE SectionHandle,
    _In_ ACCESS_MASK DesiredAccess,
    _In_opt_ POBJECT_ATTRIBUTES ObjectAttributes,
    _In_opt_ PLARGE_INTEGER MaximumSize,
    _In_ ULONG SectionPageProtection,
    _In_ ULONG AllocationAttributes,
    _In_opt_ HANDLE FileHandle,
    _Inout_updates_opt_(ExtendedParameterCount) PMEM_EXTENDED_PARAMETER ExtendedParameters,
    _In_ ULONG ExtendedParameterCount
    );

#endif

View code on GitHub

This function is documented in Windows Driver Kit.