From f1db0b5004674c762c8195a8d64c1de730b6aca6 Mon Sep 17 00:00:00 2001
From: dawn <dawn@tangled.org>
Date: Sun, 26 Jul 2026 22:38:37 +0000
Subject: [PATCH] spindle/microvm: key the activation config cache per repo so tenants can't poison each other's toplevels

Signed-off-by: dawn <dawn@tangled.org>
---
 cmd/spindle-microvm-run/main_linux.go | 2 +-
 spindle/engines/microvm/cid_test.go | 30 ++++++++++++++++++++++++++++++
 spindle/engines/microvm/engine.go | 9 ++++++++-
 spindle/engines/microvm/nixos_toplevel_cache.go | 11 +++++++----
 4 file(s) changed, 46 insertion(s)(+), 6 deletion(s)(-)

diff --git a/cmd/spindle-microvm-run/main_linux.go b/cmd/spindle-microvm-run/main_linux.go
--- a/cmd/spindle-microvm-run/main_linux.go
+++ b/cmd/spindle-microvm-run/main_linux.go
@@ -257,7 +257,7 @@ return fmt.Errorf("failed to open database: %w", err)
 			}
 			defer configCacheDB.Close()
 
-			configKey, err = microvm.BuildConfigKey(imageSpec, cmd.String("activate-config"))
+			configKey, err = microvm.BuildConfigKey(imageSpec, cmd.String("activate-config"), "local")
 			if err != nil {
 				return fmt.Errorf("calculate config key: %w", err)
 			}
diff --git a/spindle/engines/microvm/cid_test.go b/spindle/engines/microvm/cid_test.go
new file mode 100644
--- /dev/null
+++ b/spindle/engines/microvm/cid_test.go
@@ -0,0 +1,30 @@
+package microvm
+
+import (
+	"testing"
+)
+
+func TestBuildConfigKeyScopesByRepo(t *testing.T) {
+	spec := ImageSpec{BaseConfigHash: "deadbeef"}
+	cfg := manifestConfig{Dependencies: []string{"nodejs"}}
+
+	a, err := buildConfigKey(spec, cfg, "did:plc:aaa")
+	if err != nil {
+		t.Fatal(err)
+	}
+	b, err := buildConfigKey(spec, cfg, "did:plc:bbb")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if a == b {
+		t.Errorf("same config in different repos produced the same key %q", a)
+	}
+
+	again, err := buildConfigKey(spec, cfg, "did:plc:aaa")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if a != again {
+		t.Errorf("key not deterministic: %q vs %q", a, again)
+	}
+}
diff --git a/spindle/engines/microvm/engine.go b/spindle/engines/microvm/engine.go
--- a/spindle/engines/microvm/engine.go
+++ b/spindle/engines/microvm/engine.go
@@ -160,8 +160,15 @@ "microVM image %q is not a NixOS image: services, virtualisation, dependencies and registry workflow options require a NixOS image",
 				imageName,
 			)
 		}
+		// the cached toplevel is guest-asserted, so the cache key has to
+		// be per-repo. a global key lets one tenant poison the activation
+		// of another tenant's identical config
+		repoDid := ""
+		if md := tpl.TriggerMetadata; md != nil && md.Repo != nil {
+			repoDid = md.Repo.Did
+		}
 		var err error
-		configKey, err = buildConfigKey(imageSpec, config)
+		configKey, err = buildConfigKey(imageSpec, config, repoDid)
 		if err != nil {
 			return nil, fmt.Errorf("build config key: %w", err)
 		}
diff --git a/spindle/engines/microvm/nixos_toplevel_cache.go b/spindle/engines/microvm/nixos_toplevel_cache.go
--- a/spindle/engines/microvm/nixos_toplevel_cache.go
+++ b/spindle/engines/microvm/nixos_toplevel_cache.go
@@ -12,7 +12,8 @@
 	"tangled.org/core/spindle/db"
 )
 
-const nixosToplevelCacheSchemaVersion = 1
+// v2 keys are scoped by repo did in v1 keys were global
+const nixosToplevelCacheSchemaVersion = 2
 
 type nixosToplevelCacheRecord struct {
 	ConfigKey string    `json:"config_key"`
@@ -72,7 +73,7 @@ sum := sha256.Sum256(data)
 	return hex.EncodeToString(sum[:])
 }
 
-func buildConfigKey(imageSpec ImageSpec, cfg manifestConfig) (string, error) {
+func buildConfigKey(imageSpec ImageSpec, cfg manifestConfig, repoDid string) (string, error) {
 	baseHash, err := BaseConfigHash(imageSpec)
 	if err != nil {
 		return "", err
@@ -81,20 +82,22 @@ payload := struct {
 		Schema     int    `json:"schema"`
 		BaseConfig string `json:"base_config"`
 		UserConfig string `json:"user_config"`
+		RepoDid    string `json:"repo_did"`
 	}{
 		Schema:     nixosToplevelCacheSchemaVersion,
 		BaseConfig: baseHash,
 		UserConfig: userConfigHash(cfg),
+		RepoDid:    repoDid,
 	}
 	data, _ := json.Marshal(payload)
 	sum := sha256.Sum256(data)
 	return hex.EncodeToString(sum[:]), nil
 }
 
-func BuildConfigKey(imageSpec ImageSpec, userConfigJSON string) (string, error) {
+func BuildConfigKey(imageSpec ImageSpec, userConfigJSON string, repoDid string) (string, error) {
 	var cfg manifestConfig
 	if err := json.Unmarshal([]byte(userConfigJSON), &cfg); err != nil {
 		return "", err
 	}
-	return buildConfigKey(imageSpec, cfg)
+	return buildConfigKey(imageSpec, cfg, repoDid)
 }

--
tangled.sh