kernel: microcode in every initramfs through mkinitcpio's microcode hook (issue 1977)

Declares amd-ucode and intel-ucode, the drop-in /etc/mkinitcpio.conf.d/mesh-microcode.conf, the
initramfs script and mesh-kernel-initramfs.service; kernel_boot answers the running revision and
whether the images were built with the drop-in. Tests: 1977/AC1-AC5.

Builds: L1, L2, L3, L4, L5 (issue 1977 note 2)

modules/kernel/cmd/kernel-tools/boot.go

@@ -23,6 +23,30 @@ type BootState struct {
 	Booted          string   `json:"booted"`
 	FallbackPresent bool     `json:"fallback_present"`
 	BootFreeKiB     int64    `json:"boot_free_kib"`
+	// MicrocodeRevision is the revision the CPU runs, the first "microcode" line of /proc/cpuinfo ("" when it has none).
+	MicrocodeRevision string `json:"microcode_revision"`
+	// ImagesBuiltWithMicrocode is true when the initramfs images were last built with the microcode drop-in as it is now
+	// (novox/hq issue 1977).
+	ImagesBuiltWithMicrocode bool `json:"images_built_with_microcode"`
+}
+
+// stateDir is the module's own directory on the machine, where the initramfs script records the drop-in it built with.
+const stateDir = "var/lib/mesh-kernel"
+
+const microcodeDropIn = "etc/mkinitcpio.conf.d/mesh-microcode.conf"
+
+var cpuMicrocode = regexp.MustCompile(`(?m)^microcode\s*:\s*(\S+)`)
+
+// microcode reads the revision the CPU runs and whether the images carry the drop-in as it is now.
+func (m *Machine) microcode(b *BootState) {
+	if raw, err := m.read("proc/cpuinfo"); err == nil {
+		if r := cpuMicrocode.FindStringSubmatch(raw); r != nil {
+			b.MicrocodeRevision = r[1]
+		}
+	}
+	built, err := m.read(stateDir + "/initramfs-built")
+	now, err2 := m.read(microcodeDropIn)
+	b.ImagesBuiltWithMicrocode = err == nil && err2 == nil && built == now
 }
 
 var grubKernel = regexp.MustCompile(`(?m)^\s*linux\s+(?:/boot)?/(vmlinuz-\S+)`)
@@ -33,6 +57,7 @@ var bootImage = regexp.MustCompile(`BOOT_IMAGE=(?:/boot)?/?(\S+)`)
 // systemd-boot, a grub.cfg without it GRUB.
 func (m *Machine) Boot() (*BootState, error) {
 	b := &BootState{Loader: "none", Entries: []string{}, Kernels: []string{}}
+	m.microcode(b)
 	files, _ := filepath.Glob(m.path("boot/vmlinuz-*"))
 	for _, f := range files {
 		b.Kernels = append(b.Kernels, filepath.Base(f))