heads/initrd/bin/tpmr

#!/bin/bash
# TPM Wrapper - to unify tpm and tpm2 subcommands

. /etc/functions

SECRET_DIR="/tmp/secret"
PRIMARY_HANDLE="0x81000000"
ENC_SESSION_FILE="enc.ctx"
DEC_SESSION_FILE="dec.ctx"
PRIMARY_HANDLE_FILE="primary.handle"

# PCR size in bytes.  Set when we determine what TPM version is in use.
# TPM1 PCRs are always 20 bytes.  TPM2 is allowed to provide multiple PCR banks
# with different algorithms - we always use SHA-256, so they are 32 bytes.
PCR_SIZE=

# Export CONFIG_TPM2_CAPTURE_PCAP=y from your board config to capture tpm2 pcaps to
# /tmp/tpm0.pcap; Wireshark can inspect these.  (This must be enabled at build
# time so the pcap TCTI driver is included.)
if [ -n "$CONFIG_TPM2_CAPTURE_PCAP" ]; then
	export TPM2TOOLS_TCTI="pcap:device:/dev/tpmrm0"
	export TCTI_PCAP_FILE="/tmp/tpm0.pcap"
fi

set -e -o pipefail
if [ -r "/tmp/config" ]; then
	. /tmp/config
else
	. /etc/config
fi

TRACE "Under /bin/tpmr"

# Busybox xxd lacks -r, and we get hex dumps from TPM1 commands.  This converts
# a hex dump to binary data using sed and printf
hex2bin() {
	sed 's/\([0-9A-F]\{2\}\)/\\\\\\x\1/gI' | xargs printf
}

# Render a password as 'hex:<hexdump>' for use with tpm2-tools.  Passwords
# should always be passed this way to avoid ambiguity.  (Passing with no prefix
# would choke if the password happened to start with 'file:' or 'hex:'.  Passing
# as a file still chokes if the password begins with 'hex:', oddly tpm2-tools
# accepts 'hex:' in the file content.)
tpm2_password_hex() {
	echo "hex:$(echo -n "$1" | xxd -p | tr -d ' \n')"
}

# usage: tpmr pcrread [-a] <index> <file>
# Reads PCR binary data and writes to file.
# -a: Append to file.  Default is to overwrite.
tpm2_pcrread() {
	TRACE "Under /bin/tpmr:tpm2_pcrread"
	if [ "$1" = "-a" ]; then
		APPEND=y
		shift
	fi

	index="$1"
	file="$2"

	if [ -z "$APPEND" ]; then
		# Don't append - truncate file now so real command always
		# appends
		true >"$file"
	fi

	DO_WITH_DEBUG tpm2 pcrread -Q -o >(cat >>"$file") "sha256:$index"
}
tpm1_pcrread() {
	TRACE "Under /bin/tpmr:tpm1_pcrread"
	if [ "$1" = "-a" ]; then
		APPEND=y
		shift
	fi

	index="$1"
	file="$2"

	if [ -z "$APPEND" ]; then
		# Don't append - truncate file now so real command always
		# appends
		true >"$file"
	fi

	DO_WITH_DEBUG tpm pcrread -ix "$index" | hex2bin >>"$file"
}

# usage: tpmr calcfuturepcr [-a] <input_file> <output_file>
# Uses the scratch PCR to calculate a future PCR value (TPM2 23, TPM1 16). The
# data in input file are hashed into a PCR, and the PCR value is placed in
# output_file.
# -a: Append to output_file.  Default is to overwrite
tpm2_calcfuturepcr() {
	TRACE "Under /bin/tpmr:tpm2_calcfuturepcr"
	if [ "$1" = "-a" ]; then
		APPEND=y
		shift
	fi

	input_file="$1"
	output_file="$2"

	if [ -z "$APPEND" ]; then
		true >"$output_file"
	fi

	tpm2 pcrreset -Q 23
	DO_WITH_DEBUG tpmr extend -ix 23 -if "$input_file"
	DO_WITH_DEBUG tpm2 pcrread -Q -o >(cat >>"$output_file") sha256:23
	tpm2 pcrreset -Q 23
}
tpm1_calcfuturepcr() {
	TRACE "Under /bin/tpmr:tpm1_calcfuturepcr"
	if [ "$1" = "-a" ]; then
		APPEND=y
		shift
	fi

	input_file="$1"
	output_file="$2"

	if [ -z "$APPEND" ]; then
		true >"$output_file"
	fi

	DO_WITH_DEBUG tpm calcfuturepcr -ix 16 -if "$input_file" | hex2bin >>"$output_file"
}

tpm2_extend() {
	TRACE "Under /bin/tpmr:tpm2_extend"
	while true; do
		case "$1" in
			-ix)
				index="$2"
				shift 2;;
			-ic)
				hash="$(echo -n "$2"|sha256sum|cut -d' ' -f1)"
				shift 2;;
			-if)
				hash="$(sha256sum "$2"|cut -d' ' -f1)"
				shift 2;;
			*)
				break;;
		esac
	done
	tpm2 pcrextend "$index:sha256=$hash"
	DO_WITH_DEBUG tpm2 pcrread "sha256:$index"
}

tpm2_counter_read() {
	TRACE "Under /bin/tpmr:tpm2_counter_read"
	while true; do
		case "$1" in
			-ix)
				index="$2"
				shift 2;;
			*)
				break;;
		esac
	done
	echo "$index: `tpm2 nvread 0x$index | xxd -pc8`"
}

tpm2_counter_inc() {
	TRACE "Under /bin/tpmr:tpm2_counter_inc"
	while true; do
		case "$1" in
			-ix)
				index="$2"
				shift 2;;
			-pwdc)
				pwd="$2"
				shift 2;;
			*)
				break;;
		esac
	done
	tpm2 nvincrement "0x$index" > /dev/console
	echo "$index: `tpm2 nvread 0x$index | xxd -pc8`"
}

tpm2_counter_cre() {
	TRACE "Under /bin/tpmr:tpm2_counter_cre"
	while true; do
		case "$1" in
			-pwdo)
				pwdo="$2"
				shift 2;;
			-pwdof)
				pwdo="file:$2"
				shift 2;;
			-pwdc)
				pwd="$2"
				shift 2;;
			-la)
				label="$2"
				shift 2;;
			*)
				break;;
		esac
	done
	rand_index="1`dd if=/dev/urandom bs=1 count=3 | xxd -pc3`"
	tpm2 nvdefine -C o -s 8 -a "ownerread|authread|authwrite|nt=1" \
		-P "$(tpm2_password_hex "$pwdo")" "0x$rand_index" > /dev/console
	echo "$rand_index: (valid after an increment)"
}

tpm2_startsession() {
	TRACE "Under /bin/tpmr:tpm2_startsession"
	mkdir -p "$SECRET_DIR"
	tpm2 flushcontext -Q \
		--transient-object \
		|| die "tpm2_flushcontext: unable to flush transient handles"

	tpm2 flushcontext -Q \
		--loaded-session \
		|| die "tpm2_flushcontext: unable to flush sessions"

	tpm2 flushcontext -Q \
		--saved-session \
		|| die "tpm2_flushcontext: unable to flush saved session"
	tpm2 readpublic -Q -c "$PRIMARY_HANDLE" -t "/tmp/$PRIMARY_HANDLE_FILE"
	tpm2 startauthsession -Q -c "/tmp/$PRIMARY_HANDLE_FILE" --hmac-session -S "/tmp/$ENC_SESSION_FILE"
	tpm2 startauthsession -Q -c "/tmp/$PRIMARY_HANDLE_FILE" --hmac-session -S "/tmp/$DEC_SESSION_FILE"
	tpm2 sessionconfig -Q --disable-encrypt "/tmp/$DEC_SESSION_FILE"
}

# Trap EXIT with cleanup_session() to release a TPM2 session and delete the
# session file.  E.g.:
#   trap "cleanup_session '$SESSION_FILE'" EXIT
cleanup_session() {
	TRACE "Under /bin/tpmr:cleanup_session"
	session_file="$1"
	if [ -f "$session_file" ]; then
		DEBUG "Clean up session: $session_file"
		# Nothing else we can do if this fails, still remove the file
		tpm2 flushcontext -Q "$session_file" || DEBUG "Flush failed for session $session_file"
		rm -f "$session_file"
	else
		DEBUG "No need to clean up session: $session_file"
	fi
}

# Clean up a file by shredding it.  No-op if the file wasn't created.  Use with
# trap EXIT, e.g.:
#   trap "cleanup_shred '$FILE'" EXIT
cleanup_shred() {
	TRACE "Under /bin/tpmr:cleanup_shred"
	shred -n 10 -z -u "$1" 2>/dev/null || true
}

# tpm2_seal: Seal a file against PCR values and, optionally, a password.
# If a password is given, both the PCRs and password are required to unseal the
# file.  PCRs are provided as a PCR list and data file.  PCR data must be
# provided - TPM2 allows the TPM to fall back to current PCR values, but it is
# not required to support this.
tpm2_seal() {
	TRACE "Under /bin/tpmr:tpm2_seal"
	file="$1" #$KEY_FILE
	index="$2"
	pcrl="$3" #0,1,2,3,4,5,6,7 (does not include algorithm prefix)
	pcrf="$4"
	sealed_size="$5"	# Not used for TPM2
	pass="$6"

	mkdir -p "$SECRET_DIR"
	bname="`basename $file`"

	# Pad with up to 6 zeros, i.e. '0x81000001', '0x81001234', etc.
	handle="$(printf "0x81%6s" "$index" | tr ' ' 0)"

	DEBUG "tpm2_seal: file=$file handle=$handle pcrl=$pcrl pcrf=$pcrf pass=$(mask_param "$pass")"

	# Create a policy requiring both PCRs and the object's authentication
	# value using a trial session.
	TRIAL_SESSION=/tmp/sealfile_trial.session
	AUTH_POLICY=/tmp/sealfile_auth.policy
	rm -f "$TRIAL_SESSION" "$AUTH_POLICY"
	tpm2 startauthsession -g sha256 -S "$TRIAL_SESSION"
	# We have to clean up the session
	trap "cleanup_session '$TRIAL_SESSION'" EXIT
	# Save the policy hash in case the password policy is not used (we have
	# to get this from the last step, whichever it is).
	tpm2 policypcr -Q -l "sha256:$pcrl" -f "$pcrf" -S "$TRIAL_SESSION" -L "$AUTH_POLICY"
	CREATE_PASS_ARGS=()
	if [ "$pass" ]; then
		# Add an object authorization policy (the object authorization
		# will be the password).  Save the digest, this is the resulting
		# policy.
		tpm2 policypassword -Q -S "$TRIAL_SESSION" -L "$AUTH_POLICY"
		# Pass the password to create later.  Pass the sha256sum of the
		# password to the TPM so the password is not limited to 32 chars
		# in length.
		CREATE_PASS_ARGS=(-p "$(tpm2_password_hex "$pass")")
	fi

	# Create the object with this policy and the auth value.
	# NOTE: We disable USERWITHAUTH and enable ADMINWITHPOLICY so the
	# password cannot be used on its own, the PCRs are also required.
	# (The default is to allow either policy auth _or_ password auth.  In
	# this case the policy includes the password, and we don't want to allow
	# the password on its own.)
	tpm2 create -Q -C "/tmp/$PRIMARY_HANDLE_FILE" \
		-i "$file" \
		-u "$SECRET_DIR/$bname.priv" \
		-r "$SECRET_DIR/$bname.pub" \
		-L "$AUTH_POLICY" \
		-S "/tmp/$DEC_SESSION_FILE" \
		-a "fixedtpm|fixedparent|adminwithpolicy" \
		"${CREATE_PASS_ARGS[@]}"

	tpm2 load -Q -C "/tmp/$PRIMARY_HANDLE_FILE" \
		-u "$SECRET_DIR/$bname.priv" -r "$SECRET_DIR/$bname.pub" \
		-c "$SECRET_DIR/$bname.seal.ctx"
	read -s -p "TPM owner password: " key_password
	echo # new line after password prompt
	# remove possible data occupying this handle
	tpm2 evictcontrol -Q -C o -P "$(tpm2_password_hex "$key_password")" \
		-c "$handle" 2>/dev/null || true
	DO_WITH_DEBUG --mask-position 6 \
		tpm2 evictcontrol -Q -C o -P "$(tpm2_password_hex "$key_password")" \
		-c "$SECRET_DIR/$bname.seal.ctx" "$handle"
}
tpm1_seal() {
	TRACE "Under /bin/tpmr:tpm1_seal"
	file="$1"
	index="$2"
	pcrl="$3" #0,1,2,3,4,5,6,7 (does not include algorithm prefix)
	pcrf="$4"
	sealed_size="$5"
	pass="$6"

	sealed_file="$SECRET_DIR/tpm1_seal_sealed.bin"
	trap "cleanup_shred '$sealed_file'" EXIT

	POLICY_ARGS=()

	# If a password was given, add it to the policy arguments
	if [ "$pass" ]; then
		POLICY_ARGS+=(-pwdd "$pass")
	fi

	# Transform the PCR list and PCR file to discrete arguments
	IFS=',' read -r -a PCR_LIST <<<"$pcrl"
	pcr_file_index=0
	for pcr in "${PCR_LIST[@]}"; do
		# Read each PCR_SIZE block from the file and pass as hex
		POLICY_ARGS+=(-ix "$pcr"
			"$(dd if="$pcrf" skip="$pcr_file_index" bs="$PCR_SIZE" count=1 status=none | xxd -p | tr -d ' ')"
			)
		pcr_file_index=$((pcr_file_index+1))
	done

	tpm sealfile2 \
		-if "$file" \
		-of "$sealed_file" \
		-hk 40000000 \
		"${POLICY_ARGS[@]}"

	# try it without the owner password first
	if ! tpm nv_writevalue -in "$index" -if "$sealed_file"; then
		# to create an nvram space we need the TPM owner password
		# and the TPM physical presence must be asserted.
		#
		# The permissions are 0 since there is nothing special
		# about the sealed file
		tpm physicalpresence -s \
			|| warn "Warning: Unable to assert physical presence"

		read -s -p "TPM Owner password: " tpm_password
		echo

		tpm nv_definespace -in "$index" -sz "$sealed_size" \
			-pwdo "$tpm_password" -per 0 \
			|| warn "Warning: Unable to define NVRAM space; trying anyway"


		tpm nv_writevalue -in "$index" -if "$sealed_file" \
			|| die "Unable to write sealed secret to NVRAM"
	fi
}

# Unseal a file sealed by tpm2_seal.  The PCR list must be provided, the
# password must be provided if one was used to seal (and cannot be provided if
# no password was used to seal).
tpm2_unseal() {
	TRACE "Under /bin/tpmr:tpm2_unseal"
	index="$1"
	pcrl="$2" #0,1,2,3,4,5,6,7 (does not include algorithm prefix)
	sealed_size="$3"
	file="$4"
	pass="$5"

	# TPM2 doesn't care about sealed_size, only TPM1 needs that.  We don't
	# have to separately read the sealed file on TPM2.

	# Pad with up to 6 zeros, i.e. '0x81000001', '0x81001234', etc.
	handle="$(printf "0x81%6s" "$index" | tr ' ' 0)"

	DEBUG "tpm2_unseal: handle=$handle pcrl=$pcrl file=$file pass=$(mask_param "$pass")"

	# If we don't have the primary handle (TPM hasn't been reset), tpm2 will
	# print nonsense error messages about an unexpected handle value.  We
	# can't do anything without a primary handle.
	if [ ! -f "/tmp/$PRIMARY_HANDLE_FILE" ]; then
		DEBUG "tpm2_unseal: No primary handle, cannot attempt to unseal"
		exit 1
	fi

	POLICY_SESSION=/tmp/unsealfile_policy.session
	rm -f "$POLICY_SESSION"
	tpm2 startauthsession -Q -g sha256 -S "$POLICY_SESSION" --policy-session
	trap "cleanup_session '$POLICY_SESSION'" EXIT
	# Check the PCR policy
	tpm2 policypcr -Q -l "sha256:$pcrl" -S "$POLICY_SESSION"
	UNSEAL_PASS_SUFFIX=""

	if [ "$pass" ]; then
		# Add the object authorization policy (the actual password is
		# provided later, but we must include this so the policy we
		# attempt to use is correct).
		tpm2 policypassword -Q -S "$POLICY_SESSION"
		# When unsealing, include the password with the auth session
		UNSEAL_PASS_SUFFIX="+$(tpm2_password_hex "$pass")"
	fi

	tpm2 unseal -Q -c "$handle" -p "session:$POLICY_SESSION$UNSEAL_PASS_SUFFIX" \
		-S "/tmp/$ENC_SESSION_FILE" > "$file"
}
tpm1_unseal() {
	TRACE "Under /bin/tpmr:tpm1_unseal"
	index="$1"
	pcrl="$2"
	sealed_size="$3"
	file="$4"
	pass="$5"

	# pcrl (the PCR list) is unused in TPM1.  The TPM itself knows which
	# PCRs were used to seal and checks them.  We can't verify that it's
	# correct either, so just ignore it in TPM1.

	sealed_file="$SECRET_DIR/tpm1_unseal_sealed.bin"
	trap "cleanup_shred '$sealed_file'" EXIT

	rm -f "$sealed_file"

	tpm nv_readvalue \
		-in "$index" \
		-sz "$sealed_size" \
		-of "$sealed_file" \
		|| die "Unable to read sealed file from TPM NVRAM"

	PASS_ARGS=()
	if [ "$pass" ]; then
		PASS_ARGS=(-pwdd "$pass")
	fi

	tpm unsealfile \
		-if "$sealed_file" \
		-of "$file" \
		"${PASS_ARGS[@]}" \
		-hk 40000000
}

tpm2_reset() {
	TRACE "Under /bin/tpmr:tpm2_reset"
	key_password="$1"
	mkdir -p "$SECRET_DIR"
	tpm2 clear -c platform || warn "Unable to clear TPM on platform hierarchy!"
	tpm2 changeauth -c owner "$(tpm2_password_hex "$key_password")"
	tpm2 createprimary -C owner -g sha256 -G "${CONFIG_PRIMARY_KEY_TYPE:-rsa}" \
		-c "$SECRET_DIR/primary.ctx" -P "$(tpm2_password_hex "$key_password")"
	tpm2 evictcontrol -C owner -c "$SECRET_DIR/primary.ctx" "$PRIMARY_HANDLE" \
		-P "$(tpm2_password_hex "$key_password")"
	shred -u "$SECRET_DIR/primary.ctx"
	tpm2_startsession

	# Set the dictionary attack parameters.  TPM2 defaults vary widely, we
	# want consistent behavior on any TPM.
	# * --max-tries=10: Allow 10 failures before lockout.  This allows the
	#   user to quickly "burst" 10 failures without significantly impacting
	#   the rate allowed for a dictionary attacker.
	#   Most TPM2 flows ask for the owner password 2-4 times, so this allows
	#   a handful of mistypes and some headroom for an expected unseal
	#   failure if firmware is updated.
	#   Remember that an auth failure is also counted any time an unclean
	#   shutdown occurs (see TPM2 spec part 1, section 19.8.6, "Non-orderly
	#   Shutdown").
	# * --recovery-time=3600: Forget an auth failure every 1 hour.
	# * --lockout-recovery-time: After a failed lockout recovery auth, the
	#   TPM must be reset to try again.
	#
	# Heads does not offer a way to reset dictionary attack lockout, instead
	# the TPM can be reset and new secrets sealed.
	tpm2 dictionarylockout -Q --setup-parameters \
		--max-tries=10 \
		--recovery-time=3600 \
		--lockout-recovery-time=0 \
		--auth="session:/tmp/$ENC_SESSION_FILE"

	# Set a random DA lockout password, so the DA lockout can't be cleared
	# with a password.  Heads doesn't offer dictionary attach reset, instead
	# the TPM can be reset and new secrets sealed.
	#
	# The default lockout password is empty, so we must set this, and we
	# don't need to provide any auth (use the default empty password).
	tpm2 changeauth -Q -c lockout \
		"hex:$(dd if=/dev/urandom bs=32 count=1 status=none | xxd -p | tr -d ' \n')"
}

# Perform final cleanup before boot and lock the platform heirarchy.
tpm2_kexec_finalize() {
	TRACE "Under /bin/tpmr:tpm2_kexec_finalize"

	# Flush sessions and transient objects
	tpm2 flushcontext -Q --transient-object \
		|| warn "tpm2_flushcontext: unable to flush transient handles"
	tpm2 flushcontext -Q --loaded-session \
		|| warn "tpm2_flushcontext: unable to flush sessions"
	tpm2 flushcontext -Q --saved-session \
		|| warn "tpm2_flushcontext: unable to flush saved session"

	# Add a random passphrase to platform hierarchy to prevent TPM2 from
	# being cleared in the OS.
	# This passphrase is only effective before the next boot.
	echo "Locking TPM2 platform hierarchy..."
	randpass=$(dd if=/dev/urandom bs=4 count=1 status=none | xxd -p)
	tpm2 changeauth -c platform "$randpass" \
		|| warn "Failed to lock platform hierarchy of TPM2!"
}

tpm2_shutdown() {
	TRACE "Under /bin/tpmr:tpm2_shutdown"

	# Prepare for shutdown.
	# This is a "clear" shutdown (do not preserve runtime state) since we
	# are not going to resume later, we are powering off (or rebooting).
	tpm2 shutdown -Q --clear
}

if [ "$CONFIG_TPM" != "y" ]; then
	echo >&2 "No TPM!"
	exit 1
fi

# TPM1 - most commands forward directly to tpm, but some are still wrapped for
# consistency with tpm2.
if [ "$CONFIG_TPM2_TOOLS" != "y" ]; then
	PCR_SIZE=20	# TPM1 PCRs are always SHA-1
	subcmd="$1"
	# Don't shift yet, for most commands we will just forward to tpm.
	case "$subcmd" in
		pcrread)
			shift; tpm1_pcrread "$@";;
		pcrsize)
			echo "$PCR_SIZE";;
		calcfuturepcr)
			shift; tpm1_calcfuturepcr "$@";;
		seal)
			shift; tpm1_seal "$@";;
		unseal)
			shift; tpm1_unseal "$@";;
		kexec_finalize)
			;;	# Nothing on TPM1.
		shutdown)
			;;	# Nothing on TPM1.
		*)
			DEBUG "Direct translation from tpmr to tpm1 call"
			DO_WITH_DEBUG exec tpm "$@"
			;;
	esac
	exit 0
fi

# TPM2 - all commands implemented as wrappers around tpm2
PCR_SIZE=32	# We use the SHA-256 PCRs
subcmd="$1"
shift 1
case "$subcmd" in
	pcrread)
		tpm2_pcrread "$@";;
	pcrsize)
		echo "$PCR_SIZE";;
	calcfuturepcr)
		tpm2_calcfuturepcr "$@";;
	extend)
		tpm2_extend "$@";;
	counter_read)
		tpm2_counter_read "$@";;
	counter_increment)
		tpm2_counter_inc "$@";;
	counter_create)
		tpm2_counter_cre "$@";;
	seal)
		tpm2_seal "$@";;
	startsession)
		tpm2_startsession "$@";;
	unseal)
		tpm2_unseal "$@";;
	reset)
		tpm2_reset "$@";;
	kexec_finalize)
		tpm2_kexec_finalize "$@";;
	shutdown)
		tpm2_shutdown "$@";;
	*)
		echo "Command $subcmd not wrapped!"
		exit 1
esac