This protocol is intended for use as a means to store data in the EFI SMM environment.
Include/Protocol/SmmVariableProtocol.h

PROTOCOL Information

PROTOCOL's Guid Name	PROTOCOL's Guid
gEfiSmmVariableProtocolGuid	{ 0xed32d533, 0x99e6, 0x4209, { 0x9c, 0xc0, 0x2d, 0x72, 0xcd, 0xd9, 0x98, 0xa7 }}

Refer to Header File