Security Model

VyomaOS achieves strong security through a simple, layered approach. Instead of filtering dangerous operations, it prevents them from existing in the first place.

Design Principle

Capabilities not declared in the manifest are never wired up — no filtering layer needed.

Traditional OS security works by granting broad access and then restricting it (allow-by-default). VyomaOS inverts this: apps get nothing unless explicitly declared (deny-by-default). There’s no filter to bypass because the interfaces simply don’t exist.

Four Security Layers

Layer 1: WASM Sandbox

Every app runs inside Wasmtime’s WebAssembly sandbox:

• Memory isolation: Each app gets its own linear memory. No raw pointers, no address space sharing.
• Control flow integrity: Execution follows the WASM control flow graph. No ROP/JOP gadgets.
• Type safety: All function calls are type-checked at the bytecode level.
• Stack overflows, buffer overruns, use-after-free — eliminated structurally.

Layer 2: WASI Capability Model

Each app declares capabilities in its vyoma.toml manifest:

[capabilities]
stdio      = true    # stdin/stdout/stderr
filesystem = true    # mount /data (9P)
network    = true    # WASI sockets (TCP)
display    = true    # framebuffer + VYOMA_DRAW
shell      = true    # @supervisor: commands
mouse      = true    # mouse input events

The supervisor reads this manifest and wires up only the declared WASI imports when spawning the Wasmtime process. If an app doesn’t declare network = true, there is no TCP socket interface to call — not even a filtered one.

Layer 3: Seccomp BPF Denylist

The supervisor applies a seccomp BPF denylist to all Wasmtime child processes. Even if Wasmtime were somehow compromised, dangerous syscalls are blocked at the kernel level.

This is a defense-in-depth measure — the WASM sandbox and capability model should prevent any need for it, but it provides an additional barrier.

Layer 4: No C Userland

VyomaOS has no shell, no libc, no interpreters, no POSIX environment variables, no /proc filesystem. The entire attack surface is:

• Linux kernel (minimal allnoconfig build)
• Wasmtime runtime
• Rust supervisor

That’s it. No shared libraries, no dynamic linker, no script interpreters, no package managers running as root. Every traditional userland attack vector is absent.

Capability Reference

Capability	What it provides	What’s absent without it
stdio	stdin/stdout/stderr	No console I/O
filesystem	Mount /data (9P, persistent)	No file access
network	WASI sockets (TCP)	No network interface
display	Framebuffer + VYOMA_DRAW	No screen output
shell	@supervisor: commands	No process management
mouse	VYOMA_INPUT:mouse: events	No mouse input
watchdog_secs	Supervisor kills if silent N seconds	No watchdog

Comparison with Other Approaches

Approach	VyomaOS	Linux (traditional)	Docker/OCI	Android
Default access	Deny-all	Allow-all	Host kernel	Managed runtime
Filtering	Not needed	seccomp, AppArmor, SELinux	seccomp, namespaces	SELinux, permissions
Binary format	WASM (sandboxed)	ELF (native)	ELF (native)	DEX + native
Capability granularity	Per-interface	File-level	Container-level	Permission groups