forked from u-root/u-root
/
tpm.go
193 lines (159 loc) · 4.74 KB
/
tpm.go
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// Copyright 2019 the u-root Authors. All rights reserved
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package tpm reads and extends pcrs with measurements.
package tpm
import (
"bytes"
"crypto/sha256"
"encoding/binary"
"errors"
"fmt"
"io"
"log"
"github.com/google/go-tpm/tpm2"
slaunch "github.com/u-root/u-root/pkg/securelaunch"
"github.com/u-root/u-root/pkg/securelaunch/eventlog"
"github.com/u-root/u-root/pkg/tss"
)
var hashAlgo = tpm2.AlgSHA256
var tpmHandle *tss.TPM
// marshalPcrEvent writes structure fields piecemeal to buffer.
func marshalPcrEvent(pcr uint32, h []byte, eventDesc []byte) ([]byte, error) {
const baseTypeTXT = 0x400 // TXT specification base event value for DRTM values
const slaunchType = uint32(baseTypeTXT + 0x102) // Secure Launch event log entry type.
count := uint32(1)
eventDescLen := uint32(len(eventDesc))
slaunch.Debug("marshalPcrEvent: pcr=[%v], slaunchType=[%v], count=[%v], hashAlgo=[%v], eventDesc=[%s], eventDescLen=[%v]",
pcr, slaunchType, count, hashAlgo, eventDesc, eventDescLen)
endianess := binary.LittleEndian
var buf bytes.Buffer
if err := binary.Write(&buf, endianess, pcr); err != nil {
return nil, err
}
if err := binary.Write(&buf, endianess, slaunchType); err != nil {
return nil, err
}
if err := binary.Write(&buf, endianess, count); err != nil {
return nil, err
}
for i := uint32(0); i < count; i++ {
if err := binary.Write(&buf, endianess, hashAlgo); err != nil {
return nil, err
}
if err := binary.Write(&buf, endianess, h); err != nil {
return nil, err
}
}
if err := binary.Write(&buf, endianess, eventDescLen); err != nil {
return nil, err
}
if err := binary.Write(&buf, endianess, eventDesc); err != nil {
return nil, err
}
return buf.Bytes(), nil
}
// sendEventToSysfs marshals measurement events and writes them to sysfs.
func sendEventToSysfs(pcr uint32, h []byte, eventDesc []byte) {
b, err := marshalPcrEvent(pcr, h, eventDesc)
if err != nil {
log.Println(err)
}
if e := eventlog.Add(b); e != nil {
log.Println(e)
}
}
/*
* hashReader calculates the sha256 sum of an io reader.
*/
func hashReader(f io.Reader) []byte {
h := sha256.New()
if _, err := io.Copy(h, f); err != nil {
log.Fatal(err)
}
return h.Sum(nil)
}
/*
* New sets up a tpm device handle
* that can be used for storing hashes.
*/
func New() error {
tpm, err := tss.NewTPM()
if err != nil {
return fmt.Errorf("couldn't talk to TPM Device: err=%v", err)
}
tpmHandle = tpm
return nil
}
/*
* Close ends connection to a tpm device handle
*/
func Close() {
if tpmHandle != nil {
tpmHandle.Close()
tpmHandle = nil
}
}
/*
* readPCR reads pcr#x, where x is provided by 'pcr' arg and returns
* the result in a byte slice.
* 'tpmHandle' is the tpm device that owns the 'pcr'.
* err is returned if read fails.
*/
func readPCR(pcr uint32) ([]byte, error) {
if tpmHandle == nil {
return nil, errors.New("tpmHandle is nil")
}
val, err := tpmHandle.ReadPCR(pcr)
if err != nil {
return nil, fmt.Errorf("can't read PCR %d, err= %v", pcr, err)
}
return val, nil
}
/*
* extendPCR writes the measurements passed as 'hash' arg to pcr#x,
* where x is provided by 'pcr' arg.
*
* pcr is owned by 'tpm2Handle', a tpm device handle.
* err is returned if write to pcr fails.
*/
func extendPCR(pcr uint32, hash []byte) error {
if tpmHandle == nil {
return errors.New("tpmHandle is nil")
}
return tpmHandle.Extend(hash, pcr)
}
/*
* ExtendPCRDebug extends a PCR with the contents of a byte slice
* and notifies the kernel of this measurement by sending event via sysfs.
*
* In debug mode, it prints
* 1. old pcr value before the hash is written to pcr
* 2. new pcr values after hash is written to pcr
* 3. compares old and new pcr values and prints error if they are not
*/
func ExtendPCRDebug(pcr uint32, data io.Reader, eventDesc string) error {
oldPCRValue, err := readPCR(pcr)
if err != nil {
return fmt.Errorf("readPCR failed, err=%v", err)
}
slaunch.Debug("ExtendPCRDebug: oldPCRValue = [%x]", oldPCRValue)
hash := hashReader(data)
slaunch.Debug("Adding hash=[%x] to PCR #%d", hash, pcr)
if e := extendPCR(pcr, hash); e != nil {
return fmt.Errorf("can't extend PCR %d, err=%v", pcr, e)
}
slaunch.Debug(eventDesc)
// send event if PCR was successfully extended above.
sendEventToSysfs(pcr, hash, []byte(eventDesc))
newPCRValue, err := readPCR(pcr)
if err != nil {
return fmt.Errorf("readPCR failed, err=%v", err)
}
slaunch.Debug("ExtendPCRDebug: newPCRValue = [%x]", newPCRValue)
finalPCR := hashReader(bytes.NewReader(append(oldPCRValue, hash...)))
if !bytes.Equal(finalPCR, newPCRValue) {
return fmt.Errorf("PCRs not equal, got %x, want %x", finalPCR, newPCRValue)
}
return nil
}