keystone-zig-sm

name	keystone-zig-sm
description	Develops the M-mode Security Monitor in keystone-zig. Use when editing sm/, trap handlers, SBI dispatch, enclave create/destroy/run, or M-mode boot.

Security Monitor Development

Boot sequence

sm/boot.S:_start → smEntry → PMP map → delegate → mret → kernel

Trap handling

• mtvec points to mTrapHandler
• S-mode ecall (mcause=11) → handleSbiEcall
• Read syscall args with gpr.read("aN"), never csr.read for a0–a7
• Return via gpr.write("a0"/"a1") + advance mepc by 4

SBI dispatch table

FID	Handler	Context
2001	smCreateEnclave	Host
2002	smDestroyEnclave	Host
2003	smRunEnclave	Host
2005	smResumeEnclave	Host
3004	smStopEnclave	Enclave
3006	smExitEnclave	Enclave

Add new FIDs in lib/sbi.zig first, then implement in sm/main.zig.

Enclave state machine

invalid → allocated → fresh → running → stopped → destroying

Managed in lib/enclave.zig (enclave.Table).

Phase 2: context switch checklist

• Save host satp, mepc, mstatus, GPRs on enclave entry
• Deny host PMP entries for EPM; grant enclave entries
• First run: pass RuntimeParams in a1–a7 per Keystone convention
• On exit: reverse PMP, restore host context

Testing

zig build
zig build qemu   # UART trace: SM boot → kernel stub → create enclave

Files

• sm/main.zig — logic
• sm/boot.S — reset vector, stack
• sm/linker.ld — SM at 0x8000_0000