Introduce io386 to heads and use it to finalize chipset at runtime

On some newer platforms of intel (confirmed on nehalem, sandy/ivy
bridge), coreboot after commit [2ac149d294af795710eb4bb20f093e9920604abd](https://review.coreboot.org/cgit/coreboot.git/commit/?id=2ac149d294af795710eb4bb20f093e9920604abd)
registers an SMI to lockdown some registers on the chipset, as well
as access to the SPI flash, optionally. The SMI will always be triggered
by coreboot during S3 resume, but can be triggered by either coreboot
or the payload during normal boot path.

Enabling lockdown access to SPI flash will effectly write-protect it,
but there is no runtime option for coreboot to control it, so letting
coreboot to trigger such SMI will leave the owner of the machine lost
any possibility to program the SPI flash with its own OS, and becomes
a nightmare if the machine is uneasy to disassemble, so a scheme could
be implement, in which the SMI to lockdown chipset and SPI flash is left
for a payload to trigger, and temporarily disabling such triggering in
order to program the SPI flash needs authentication.

I have implemented a passcode-protected runtime-disableable lockdown
with grub, described [here](https://github.com/hardenedlinux/Debian-GNU-Linux-Profiles/blob/master/docs/hardened_boot/grub-for-coreboot.md#update-for-coreboot-after-commit-2ac149d294af795710eb4bb20f093e9920604abd). In order to implement a similar scheme for
Heads, I wrote [io386](https://github.com/hardenedlinux/io386).

With this commit, io386 will be called before entering boot routine
and recovery shell to trigger the SMI to finalize the chipset and
write protect the SPI flash at the same time. If the owner of the
machine want to program the SPI flash, they can enter the "flash mode"
in which the SMI is never triggered, thus SPI flash is writable.
To enter such mode, they should authencate themselves by connecting
their OpenPGP card to the machine, in order to prove they hold the very
same secret key used to sign the boot file list used by Heads.

Makefile

@@ -328,6 +328,7 @@ bin_modules-$(CONFIG_LVM2) += lvm2
 bin_modules-$(CONFIG_DROPBEAR) += dropbear
 bin_modules-$(CONFIG_FLASHTOOLS) += flashtools
 bin_modules-$(CONFIG_NEWT) += newt
+bin_modules-$(CONFIG_IO386) += io386
 
 $(foreach m, $(bin_modules-y), \
 	$(call map,initrd_bin_add,$(call bins,$m)) \

initrd/bin/flashmode

@@ -0,0 +1,46 @@
+#!/bin/sh
+. /etc/config
+. /etc/functions
+
+
+echo >&2 "!!!!! Please authenticate with OpenPGP card to prove you own this box..."
+
+confirm_gpg_card
+
+# Perform a signing-based challenge-response,
+# to authencate that the card plugged in holding
+# the key to sign the list of boot files.
+CR_NONCE="/tmp/secret/cr_nonce"
+CR_SIG="/tmp/secret/cr_nonce.sig"
+
+dd \
+	if=/dev/urandom \
+	of="$CR_NONCE" \
+	count=1 \
+	bs=20 \
+	2>/dev/null \
+|| die "Unable to generate 20 random bytes"
+
+for tries in 1 2 3; do
+	if gpg --digest-algo SHA256 \
+		--detach-sign \
+		-o "$CR_SIG" \
+		"$CR_NONCE" \
+		&& gpgv "$CR_SIG" "$CR_NONCE" \
+	; then
+		# Remove any temporary secret files that might be hanging around
+		# but recreate the directory so that new tools can use it.
+		rm -rf /tmp/secret
+		mkdir -p /tmp/secret
+		if [ "$CONFIG_TPM" = y ]; then
+			tpm extend -ix 4 -ic flashing
+		fi
+		echo >&2 "!!!!! Starting shell for ROM flashing"
+		sleep 1
+		exec /bin/ash
+	else
+		rm "$CR_SIG"
+	fi
+done
+
+die "Authentication failed! You are not allowed to program the flash."

initrd/bin/generic-init

@@ -21,6 +21,7 @@ while true; do
 	echo "r) Recovery boot"
 	echo "u) USB boot"
 	echo "m) Boot menu"
+	echo "f) ROM flashing"
 
 	if ! confirm_totp "Boot mode"; then
 		recovery 'Failed to unseal TOTP'
@@ -40,24 +41,40 @@ while true; do
 	fi
 
 	if [ "$totp_confirm" = "u" ]; then
+		if [ "$CONFIG_IO386" = y ]; then
+			lock_chip
+		fi
 		exec /bin/usb-init
 		continue
 	fi
 
+	if [ "$totp_confirm" = "f" ]; then
+		flashmode \
+		|| recovery "Failed to enter flash mode"
+	fi
+
 	if [ "$totp_confirm" = "m" ]; then
 		# Try to select a kernel from the menu
+		if [ "$CONFIG_IO386" = y ]; then
+			lock_chip
+		fi
 		mount_boot
 		kexec-select-boot -m -b /boot -c "grub.cfg"
 		continue
 	fi
 
 	if [ "$totp_confirm" = "y" -o -n "$totp_confirm" ]; then
 		# Try to boot the default
+		if [ "$CONFIG_IO386" = y ]; then
+			lock_chip
+		fi
 		mount_boot
 		kexec-select-boot -b /boot -c "grub.cfg" \
 		|| recovery "Failed default boot"
 	fi
 
+
+
 done
 
 recovery "Something failed during boot"

initrd/etc/functions

@@ -10,6 +10,13 @@ warn() {
 	echo >&2 "$*";
 }
 
+lock_chip() {
+	APM_CNT=0xb2
+	FIN_CODE=0xcb
+	echo "Finalizing chipset"
+	io386 -o b -b x $APM_CNT $FIN_CODE
+}
+
 recovery() {
 	echo >&2 "!!!!! $*"
 
@@ -20,12 +27,16 @@ recovery() {
 	if [ "$CONFIG_TPM" = y ]; then
 		tpm extend -ix 4 -ic recovery
 	fi
+
+	if [ "$CONFIG_IO386" = y ]; then
+		lock_chip
+	fi
+
 	echo >&2 "!!!!! Starting recovery shell"
 	sleep 1
 	exec /bin/ash
 }
 
-
 pcrs() {
 	head -7 /sys/class/tpm/tpm0/pcrs
 }
@@ -126,7 +137,6 @@ confirm_gpg_card()
 	|| die "gpg card read failed"
 }
 
-
 check_tpm_counter()
 {
 	# if the /boot.hashes file already exists, read the TPM counter ID

modules/io386

@@ -0,0 +1,28 @@
+modules-$(CONFIG_IO386) += io386
+
+io386_depends := $(musl_dep)
+
+io386_version := git
+io386_repo := https://github.com/hardenedlinux/io386
+io386_dir := io386-$(io386_version)
+
+io386_target := \
+	$(MAKE_JOBS) \
+	$(CROSS_TOOLS) \
+	SHARED=yes \
+	PREFIX="/" \
+	&& \
+	$(MAKE) \
+	-C $(build)/$(io386_dir) \
+	$(CROSS_TOOLS) \
+	SHARED=yes \
+	PREFIX="/" \
+	DESTDIR="$(INSTALL)" \
+	install \
+
+io386_output := \
+	io386
+
+io386_libraries :=
+
+io386_configure :=