NtSetSystemEnvironmentValueEx - NtDoc

#ifndef _NTEXAPI_H
#if (PHNT_MODE != PHNT_MODE_KERNEL)

/**
 * Sets the value of the specified firmware environment variable and the attributes that indicate how this variable is stored and maintained.
 * 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 the new value for the firmware environment variable.
 * @param BufferLength The size of the pValue buffer, in bytes.
 * Unless the VARIABLE_ATTRIBUTE_APPEND_WRITE, VARIABLE_ATTRIBUTE_AUTHENTICATED_WRITE_ACCESS,
 * or VARIABLE_ATTRIBUTE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS variable attribute is set via dwAttributes,
 * setting this value to zero will result in the deletion of this variable.
 * @param Attributes Bitmask to set UEFI variable attributes associated with the variable.
 * @return NTSTATUS Successful or errant status.
 */
NTSYSCALLAPI
NTSTATUS
NTAPI
NtSetSystemEnvironmentValueEx(
    _In_ PUNICODE_STRING VariableName,
    _In_ PCGUID VendorGuid,
    _In_reads_bytes_opt_(BufferLength) PVOID Buffer,
    _In_ ULONG BufferLength, // 0 = delete variable
    _In_ ULONG Attributes // EFI_VARIABLE_*
    );

#endif
#endif
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#ifndef _NTZWAPI_H

NTSYSCALLAPI
NTSTATUS
NTAPI
ZwSetSystemEnvironmentValueEx(
    _In_ PUNICODE_STRING VariableName,
    _In_ PCGUID VendorGuid,
    _In_reads_bytes_opt_(BufferLength) PVOID Buffer,
    _In_ ULONG BufferLength, // 0 = delete variable
    _In_ ULONG Attributes // EFI_VARIABLE_*
    );

#endif
View code on GitHub