Application domains in embedded systems such as Cyber-Physical Systems (CPS) and Industrial Internet of Things (IIoTs) involve smart, mobile, and interconnected devices which operate in large numbers (Devices Swarms). In this regard, it is important to have a good code verification technique that scales to device swarms and establishes trust among collaborating devices. We present a novel decentralized attestation scheme called Chain-of-trust based Self-reliant Swarm Attestation (CoSSA). We design a light-weight attestation protocol that executes in an SMM operating mode which is available in modern x86 based central processor units (CPUs) such as on Intel and AMD platforms.