chore: pause sequencer when talos installed and iso booted

Pause sequencer till the boot timeout if talos is booted from ISO/PXE, but
an existing talos is installed to disk and
`talos.iso.boot.halt_if_installed` kernel argument is set.

Fixes: #9232

Signed-off-by: Noel Georgi <git@frezbo.dev>

hack/release.toml

@@ -208,6 +208,16 @@ Starting with Talos 1.8, `console=ttyS0` kernel argument is removed from the met
 This should fix slow boot or no console output issues on most bare metal hardware.
 """
 
+    [notes.kernel-args]
+        title = "`talos.halt_if_installed` kernel argument"
+        description = """\
+Starting with Talos 1.8, ISO's generated from Boot Assets would have a new kernel argument `talos.halt_if_installed` which would pause the boot sequence until boot timeout if Talos is already installed on the disk.
+ISO generated for pre 1.8 versions would not have this kernel argument.
+
+This can be also explicitly enabled by setting `talos.halt_if_installed=1` in kernel argument.
+"""
+
+
 [make_deps]
 
     [make_deps.tools]

internal/app/machined/pkg/runtime/v1alpha1/v1alpha1_sequencer.go

@@ -131,6 +131,15 @@ func (*Sequencer) Initialize(r runtime.Runtime) []runtime.Phase {
 			},
 			"wipeDisks",
 			ResetSystemDiskPartitions,
+		).AppendWithDeferredCheck(
+			func() bool {
+				haltIfInstalledStr := procfs.ProcCmdline().Get(constants.KernelParamHaltIfInstalled).First()
+				haltIfInstalled, _ := strconv.ParseBool(pointer.SafeDeref(haltIfInstalledStr)) //nolint:errcheck
+
+				return r.State().Machine().Installed() && haltIfInstalled
+			},
+			"haltIfInstalled",
+			haltIfInstalled,
 		).AppendWithDeferredCheck(
 			func() bool {
 				return r.State().Machine().Installed()

internal/app/machined/pkg/runtime/v1alpha1/v1alpha1_sequencer_tasks.go

@@ -1924,6 +1924,25 @@ func UnmountEFIPartition(runtime.Sequence, any) (runtime.TaskExecutionFunc, stri
 	}, "unmountEFIPartition"
 }
 
+// haltIfInstalled halts the boot process if Talos is installed to disk but booted from ISO.
+func haltIfInstalled(seq runtime.Sequence, _ any) (runtime.TaskExecutionFunc, string) {
+	return func(ctx context.Context, logger *log.Logger, r runtime.Runtime) error {
+		ctx, cancel := context.WithTimeout(ctx, constants.BootTimeout)
+		defer cancel()
+
+		timer := time.NewTicker(30 * time.Second)
+		defer timer.Stop()
+
+		select {
+		case <-timer.C:
+			logger.Printf("Talos is already installed to disk but booted from another media and %s kernel parameter is set. Please reboot from the disk.", constants.KernelParamHaltIfInstalled)
+		case <-ctx.Done():
+		}
+
+		return nil
+	}, "haltIfInstalled"
+}
+
 // MountStatePartition mounts the system partition.
 func MountStatePartition(seq runtime.Sequence, _ any) (runtime.TaskExecutionFunc, string) {
 	return func(ctx context.Context, logger *log.Logger, r runtime.Runtime) (err error) {

pkg/imager/imager.go

@@ -336,6 +336,10 @@ func (i *Imager) buildCmdline() error {
 	// platform kernel args
 	cmdline.Append(constants.KernelParamPlatform, p.Name())
 
+	if quirks.New(i.prof.Version).SupportsHaltIfInstalled() && i.prof.Output.Kind == profile.OutKindISO {
+		cmdline.Append(constants.KernelParamHaltIfInstalled, "1")
+	}
+
 	if quirks.New(i.prof.Version).SupportsMetalPlatformConsoleTTYS0() && i.prof.Platform == constants.PlatformMetal {
 		cmdline.Append("console", "ttyS0")
 	}

pkg/machinery/constants/constants.go

@@ -84,6 +84,9 @@ const (
 	// KernelParamNetIfnames is the kernel parameter name to control predictable network interface names.
 	KernelParamNetIfnames = "net.ifnames"
 
+	// KernelParamHaltIfInstalled is the kernel parameter name to control if Talos should pause if booting from boot media while Talos is already installed.
+	KernelParamHaltIfInstalled = "talos.halt_if_installed"
+
 	// BoardNone indicates that the install is not for a specific board.
 	BoardNone = "none"
 

pkg/machinery/imager/quirks/quirks.go

@@ -111,3 +111,16 @@ func (q Quirks) SupportsMetalPlatformConsoleTTYS0() bool {
 
 	return q.v.LT(maxVersionMetalPlatformConsoleTTYS0Dropped)
 }
+
+// minVersionSupportsHalfIfInstalled is the version that supports half if installed.
+var minVersionSupportsHalfIfInstalled = semver.MustParse("1.8.0")
+
+// SupportsHaltIfInstalled returns true if the Talos version supports half if installed.
+func (q Quirks) SupportsHaltIfInstalled() bool {
+	// if the version doesn't parse, we assume it's latest Talos
+	if q.v == nil {
+		return true
+	}
+
+	return q.v.GTE(minVersionSupportsHalfIfInstalled)
+}

website/content/v1.8/reference/kernel.md

@@ -259,3 +259,8 @@ Example:
 ```text
 talos.device.settle_time=3m
 ```
+
+#### `talos.halt_if_installed`
+
+If set to `1`, Talos will pause the boot sequence and keeps printing a message until the boot timeout is reached if it detects that it is already installed.
+This is useful if booting from ISO/PXE and you want to prevent the machine accidentally booting from the ISO/PXE after installation to the disk.