core -> metropolis
Smalltown is now called Metropolis!
This is the first commit in a series of cleanup commits that prepare us
for an open source release. This one just some Bazel packages around to
follow a stricter directory layout.
All of Metropolis now lives in `//metropolis`.
All of Metropolis Node code now lives in `//metropolis/node`.
All of the main /init now lives in `//m/n/core`.
All of the Kubernetes functionality/glue now lives in `//m/n/kubernetes`.
Next steps:
- hunt down all references to Smalltown and replace them appropriately
- narrow down visibility rules
- document new code organization
- move `//build/toolchain` to `//monogon/build/toolchain`
- do another cleanup pass between `//golibs` and
`//monogon/node/{core,common}`.
- remove `//delta` and `//anubis`
Fixes T799.
Test Plan: Just a very large refactor. CI should help us out here.
Bug: T799
X-Origin-Diff: phab/D667
GitOrigin-RevId: 6029b8d4edc42325d50042596b639e8b122d0ded
diff --git a/metropolis/node/core/tpm/tpm.go b/metropolis/node/core/tpm/tpm.go
new file mode 100644
index 0000000..76f4f92
--- /dev/null
+++ b/metropolis/node/core/tpm/tpm.go
@@ -0,0 +1,561 @@
+// Copyright 2020 The Monogon Project Authors.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package tpm
+
+import (
+ "bytes"
+ "crypto"
+ "crypto/rand"
+ "crypto/rsa"
+ "crypto/x509"
+ "fmt"
+ "io"
+ "io/ioutil"
+ "os"
+ "path/filepath"
+ "strconv"
+ "strings"
+ "sync"
+ "time"
+
+ "github.com/gogo/protobuf/proto"
+ tpmpb "github.com/google/go-tpm-tools/proto"
+ "github.com/google/go-tpm-tools/tpm2tools"
+ "github.com/google/go-tpm/tpm2"
+ "github.com/google/go-tpm/tpmutil"
+ "github.com/pkg/errors"
+ "golang.org/x/sys/unix"
+
+ "git.monogon.dev/source/nexantic.git/metropolis/node/common/sysfs"
+ "git.monogon.dev/source/nexantic.git/metropolis/node/core/logtree"
+)
+
+var (
+ // SecureBootPCRs are all PCRs that measure the current Secure Boot configuration.
+ // This is what we want if we rely on secure boot to verify boot integrity. The firmware
+ // hashes the secure boot policy and custom keys into the PCR.
+ //
+ // This requires an extra step that provisions the custom keys.
+ //
+ // Some background: https://mjg59.dreamwidth.org/48897.html?thread=1847297
+ // (the initramfs issue mentioned in the article has been solved by integrating
+ // it into the kernel binary, and we don't have a shim bootloader)
+ //
+ // PCR7 alone is not sufficient - it needs to be combined with firmware measurements.
+ SecureBootPCRs = []int{7}
+
+ // FirmwarePCRs are alle PCRs that contain the firmware measurements
+ // See https://trustedcomputinggroup.org/wp-content/uploads/TCG_EFI_Platform_1_22_Final_-v15.pdf
+ FirmwarePCRs = []int{
+ 0, // platform firmware
+ 2, // option ROM code
+ 3, // option ROM configuration and data
+ }
+
+ // FullSystemPCRs are all PCRs that contain any measurements up to the currently running EFI payload.
+ FullSystemPCRs = []int{
+ 0, // platform firmware
+ 1, // host platform configuration
+ 2, // option ROM code
+ 3, // option ROM configuration and data
+ 4, // EFI payload
+ }
+
+ // Using FullSystemPCRs is the most secure, but also the most brittle option since updating the EFI
+ // binary, updating the platform firmware, changing platform settings or updating the binary
+ // would invalidate the sealed data. It's annoying (but possible) to predict values for PCR4,
+ // and even more annoying for the firmware PCR (comparison to known values on similar hardware
+ // is the only thing that comes to mind).
+ //
+ // See also: https://github.com/mxre/sealkey (generates PCR4 from EFI image, BSD license)
+ //
+ // Using only SecureBootPCRs is the easiest and still reasonably secure, if we assume that the
+ // platform knows how to take care of itself (i.e. Intel Boot Guard), and that secure boot
+ // is implemented properly. It is, however, a much larger amount of code we need to trust.
+ //
+ // We do not care about PCR 5 (GPT partition table) since modifying it is harmless. All of
+ // the boot options and cmdline are hardcoded in the kernel image, and we use no bootloader,
+ // so there's no PCR for bootloader configuration or kernel cmdline.
+)
+
+var (
+ numSRTMPCRs = 16
+ srtmPCRs = tpm2.PCRSelection{Hash: tpm2.AlgSHA256, PCRs: []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15}}
+ // TCG Trusted Platform Module Library Level 00 Revision 0.99 Table 6
+ tpmGeneratedValue = uint32(0xff544347)
+)
+
+var (
+ // ErrNotExists is returned when no TPMs are available in the system
+ ErrNotExists = errors.New("no TPMs found")
+ // ErrNotInitialized is returned when this package was not initialized successfully
+ ErrNotInitialized = errors.New("no TPM was initialized")
+)
+
+// Singleton since the TPM is too
+var tpm *TPM
+
+// We're serializing all TPM operations since it has a limited number of handles and recovering
+// if it runs out is difficult to implement correctly. Might also be marginally more secure.
+var lock sync.Mutex
+
+// TPM represents a high-level interface to a connected TPM 2.0
+type TPM struct {
+ logger logtree.LeveledLogger
+ device io.ReadWriteCloser
+
+ // We keep the AK loaded since it's used fairly often and deriving it is expensive
+ akHandleCache tpmutil.Handle
+ akPublicKey crypto.PublicKey
+}
+
+// Initialize finds and opens the TPM (if any). If there is no TPM available it returns
+// ErrNotExists
+func Initialize(logger logtree.LeveledLogger) error {
+ lock.Lock()
+ defer lock.Unlock()
+ tpmDir, err := os.Open("/sys/class/tpm")
+ if err != nil {
+ return errors.Wrap(err, "failed to open sysfs TPM class")
+ }
+ defer tpmDir.Close()
+
+ tpms, err := tpmDir.Readdirnames(2)
+ if err != nil {
+ return errors.Wrap(err, "failed to read TPM device class")
+ }
+
+ if len(tpms) == 0 {
+ return ErrNotExists
+ }
+ if len(tpms) > 1 {
+ // If this is changed GetMeasurementLog() needs to be updated too
+ logger.Warningf("Found more than one TPM, using the first one")
+ }
+ tpmName := tpms[0]
+ ueventData, err := sysfs.ReadUevents(filepath.Join("/sys/class/tpm", tpmName, "uevent"))
+ majorDev, err := strconv.Atoi(ueventData["MAJOR"])
+ if err != nil {
+ return fmt.Errorf("failed to convert uevent: %w", err)
+ }
+ minorDev, err := strconv.Atoi(ueventData["MINOR"])
+ if err != nil {
+ return fmt.Errorf("failed to convert uevent: %w", err)
+ }
+ if err := unix.Mknod("/dev/tpm", 0600|unix.S_IFCHR, int(unix.Mkdev(uint32(majorDev), uint32(minorDev)))); err != nil {
+ return errors.Wrap(err, "failed to create TPM device node")
+ }
+ device, err := tpm2.OpenTPM("/dev/tpm")
+ if err != nil {
+ return errors.Wrap(err, "failed to open TPM")
+ }
+ tpm = &TPM{
+ device: device,
+ logger: logger,
+ }
+ return nil
+}
+
+// GenerateSafeKey uses two sources of randomness (Kernel & TPM) to generate the key
+func GenerateSafeKey(size uint16) ([]byte, error) {
+ lock.Lock()
+ defer lock.Unlock()
+ if tpm == nil {
+ return []byte{}, ErrNotInitialized
+ }
+ encryptionKeyHost := make([]byte, size)
+ if _, err := io.ReadFull(rand.Reader, encryptionKeyHost); err != nil {
+ return []byte{}, errors.Wrap(err, "failed to generate host portion of new key")
+ }
+ var encryptionKeyTPM []byte
+ for i := 48; i > 0; i-- {
+ tpmKeyPart, err := tpm2.GetRandom(tpm.device, size-uint16(len(encryptionKeyTPM)))
+ if err != nil {
+ return []byte{}, errors.Wrap(err, "failed to generate TPM portion of new key")
+ }
+ encryptionKeyTPM = append(encryptionKeyTPM, tpmKeyPart...)
+ if len(encryptionKeyTPM) >= int(size) {
+ break
+ }
+ }
+
+ if len(encryptionKeyTPM) != int(size) {
+ return []byte{}, fmt.Errorf("got incorrect amount of TPM randomess: %v, requested %v", len(encryptionKeyTPM), size)
+ }
+
+ encryptionKey := make([]byte, size)
+ for i := uint16(0); i < size; i++ {
+ encryptionKey[i] = encryptionKeyHost[i] ^ encryptionKeyTPM[i]
+ }
+ return encryptionKey, nil
+}
+
+// Seal seals sensitive data and only allows access if the current platform configuration in
+// matches the one the data was sealed on.
+func Seal(data []byte, pcrs []int) ([]byte, error) {
+ lock.Lock()
+ defer lock.Unlock()
+ if tpm == nil {
+ return []byte{}, ErrNotInitialized
+ }
+ srk, err := tpm2tools.StorageRootKeyRSA(tpm.device)
+ if err != nil {
+ return []byte{}, errors.Wrap(err, "failed to load TPM SRK")
+ }
+ defer srk.Close()
+ sealedKey, err := srk.Seal(pcrs, data)
+ sealedKeyRaw, err := proto.Marshal(sealedKey)
+ if err != nil {
+ return []byte{}, errors.Wrapf(err, "failed to marshal sealed data")
+ }
+ return sealedKeyRaw, nil
+}
+
+// Unseal unseals sensitive data if the current platform configuration allows and sealing constraints
+// allow it.
+func Unseal(data []byte) ([]byte, error) {
+ lock.Lock()
+ defer lock.Unlock()
+ if tpm == nil {
+ return []byte{}, ErrNotInitialized
+ }
+ srk, err := tpm2tools.StorageRootKeyRSA(tpm.device)
+ if err != nil {
+ return []byte{}, errors.Wrap(err, "failed to load TPM SRK")
+ }
+ defer srk.Close()
+
+ var sealedKey tpmpb.SealedBytes
+ if err := proto.Unmarshal(data, &sealedKey); err != nil {
+ return []byte{}, errors.Wrap(err, "failed to decode sealed data")
+ }
+ // Logging this for auditing purposes
+ pcrList := []string{}
+ for _, pcr := range sealedKey.Pcrs {
+ pcrList = append(pcrList, string(pcr))
+ }
+ tpm.logger.Infof("Attempting to unseal data protected with PCRs %s", strings.Join(pcrList, ","))
+ unsealedData, err := srk.Unseal(&sealedKey)
+ if err != nil {
+ return []byte{}, errors.Wrap(err, "failed to unseal data")
+ }
+ return unsealedData, nil
+}
+
+// Standard AK template for RSA2048 non-duplicatable restricted signing for attestation
+var akTemplate = tpm2.Public{
+ Type: tpm2.AlgRSA,
+ NameAlg: tpm2.AlgSHA256,
+ Attributes: tpm2.FlagSignerDefault,
+ RSAParameters: &tpm2.RSAParams{
+ Sign: &tpm2.SigScheme{
+ Alg: tpm2.AlgRSASSA,
+ Hash: tpm2.AlgSHA256,
+ },
+ KeyBits: 2048,
+ },
+}
+
+func loadAK() error {
+ var err error
+ // Rationale: The AK is an EK-equivalent key and used only for attestation. Using a non-primary
+ // key here would require us to store the wrapped version somewhere, which is inconvenient.
+ // This being a primary key in the Endorsement hierarchy means that it can always be recreated
+ // and can never be "destroyed". Under our security model this is of no concern since we identify
+ // a node by its IK (Identity Key) which we can destroy.
+ tpm.akHandleCache, tpm.akPublicKey, err = tpm2.CreatePrimary(tpm.device, tpm2.HandleEndorsement,
+ tpm2.PCRSelection{}, "", "", akTemplate)
+ return err
+}
+
+// Process documented in TCG EK Credential Profile 2.2.1
+func loadEK() (tpmutil.Handle, crypto.PublicKey, error) {
+ // The EK is a primary key which is supposed to be certified by the manufacturer of the TPM.
+ // Its public attributes are standardized in TCG EK Credential Profile 2.0 Table 1. These need
+ // to match exactly or we aren't getting the key the manufacturere signed. tpm2tools contains
+ // such a template already, so we're using that instead of redoing it ourselves.
+ // This ignores the more complicated ways EKs can be specified, the additional stuff you can do
+ // is just absolutely crazy (see 2.2.1.2 onward)
+ return tpm2.CreatePrimary(tpm.device, tpm2.HandleEndorsement,
+ tpm2.PCRSelection{}, "", "", tpm2tools.DefaultEKTemplateRSA())
+}
+
+// GetAKPublic gets the TPM2T_PUBLIC of the AK key
+func GetAKPublic() ([]byte, error) {
+ lock.Lock()
+ defer lock.Unlock()
+ if tpm == nil {
+ return []byte{}, ErrNotInitialized
+ }
+ if tpm.akHandleCache == tpmutil.Handle(0) {
+ if err := loadAK(); err != nil {
+ return []byte{}, fmt.Errorf("failed to load AK primary key: %w", err)
+ }
+ }
+ public, _, _, err := tpm2.ReadPublic(tpm.device, tpm.akHandleCache)
+ if err != nil {
+ return []byte{}, err
+ }
+ return public.Encode()
+}
+
+// TCG TPM v2.0 Provisioning Guidance v1.0 7.8 Table 2 and
+// TCG EK Credential Profile v2.1 2.2.1.4 de-facto Standard for Windows
+// These are both non-normative and reference Windows 10 documentation that's no longer available :(
+// But in practice this is what people are using, so if it's normative or not doesn't really matter
+const ekCertHandle = 0x01c00002
+
+// GetEKPublic gets the public key and (if available) Certificate of the EK
+func GetEKPublic() ([]byte, []byte, error) {
+ lock.Lock()
+ defer lock.Unlock()
+ if tpm == nil {
+ return []byte{}, []byte{}, ErrNotInitialized
+ }
+ ekHandle, publicRaw, err := loadEK()
+ if err != nil {
+ return []byte{}, []byte{}, fmt.Errorf("failed to load EK primary key: %w", err)
+ }
+ defer tpm2.FlushContext(tpm.device, ekHandle)
+ // Don't question the use of HandleOwner, that's the Standard™
+ ekCertRaw, err := tpm2.NVReadEx(tpm.device, ekCertHandle, tpm2.HandleOwner, "", 0)
+ if err != nil {
+ return []byte{}, []byte{}, err
+ }
+
+ publicKey, err := x509.MarshalPKIXPublicKey(publicRaw)
+ if err != nil {
+ return []byte{}, []byte{}, err
+ }
+
+ return publicKey, ekCertRaw, nil
+}
+
+// MakeAKChallenge generates a challenge for TPM residency and attributes of the AK
+func MakeAKChallenge(ekPubKey, akPub []byte, nonce []byte) ([]byte, []byte, error) {
+ ekPubKeyData, err := x509.ParsePKIXPublicKey(ekPubKey)
+ if err != nil {
+ return []byte{}, []byte{}, fmt.Errorf("failed to decode EK pubkey: %w", err)
+ }
+ akPubData, err := tpm2.DecodePublic(akPub)
+ if err != nil {
+ return []byte{}, []byte{}, fmt.Errorf("failed to decode AK public part: %w", err)
+ }
+ // Make sure we're attesting the right attributes (in particular Restricted)
+ if !akPubData.MatchesTemplate(akTemplate) {
+ return []byte{}, []byte{}, errors.New("the key being challenged is not a valid AK")
+ }
+ akName, err := akPubData.Name()
+ if err != nil {
+ return []byte{}, []byte{}, fmt.Errorf("failed to derive AK name: %w", err)
+ }
+ return generateRSA(akName.Digest, ekPubKeyData.(*rsa.PublicKey), 16, nonce, rand.Reader)
+}
+
+// SolveAKChallenge solves a challenge for TPM residency of the AK
+func SolveAKChallenge(credBlob, secretChallenge []byte) ([]byte, error) {
+ lock.Lock()
+ defer lock.Unlock()
+ if tpm == nil {
+ return []byte{}, ErrNotInitialized
+ }
+ if tpm.akHandleCache == tpmutil.Handle(0) {
+ if err := loadAK(); err != nil {
+ return []byte{}, fmt.Errorf("failed to load AK primary key: %w", err)
+ }
+ }
+
+ ekHandle, _, err := loadEK()
+ if err != nil {
+ return []byte{}, fmt.Errorf("failed to load EK: %w", err)
+ }
+ defer tpm2.FlushContext(tpm.device, ekHandle)
+
+ // This is necessary since the EK requires an endorsement handle policy in its session
+ // For us this is stupid because we keep all hierarchies open anyways since a) we cannot safely
+ // store secrets on the OS side pre-global unlock and b) it makes no sense in this security model
+ // since an uncompromised host OS will not let an untrusted entity attest as itself and a
+ // compromised OS can either not pass PCR policy checks or the game's already over (you
+ // successfully runtime-exploited a production Smalltown Core)
+ endorsementSession, _, err := tpm2.StartAuthSession(
+ tpm.device,
+ tpm2.HandleNull,
+ tpm2.HandleNull,
+ make([]byte, 16),
+ nil,
+ tpm2.SessionPolicy,
+ tpm2.AlgNull,
+ tpm2.AlgSHA256)
+ if err != nil {
+ panic(err)
+ }
+ defer tpm2.FlushContext(tpm.device, endorsementSession)
+
+ _, err = tpm2.PolicySecret(tpm.device, tpm2.HandleEndorsement, tpm2.AuthCommand{Session: tpm2.HandlePasswordSession, Attributes: tpm2.AttrContinueSession}, endorsementSession, nil, nil, nil, 0)
+ if err != nil {
+ return []byte{}, fmt.Errorf("failed to make a policy secret session: %w", err)
+ }
+
+ for {
+ solution, err := tpm2.ActivateCredentialUsingAuth(tpm.device, []tpm2.AuthCommand{
+ {Session: tpm2.HandlePasswordSession, Attributes: tpm2.AttrContinueSession}, // Use standard no-password authentication
+ {Session: endorsementSession, Attributes: tpm2.AttrContinueSession}, // Use a full policy session for the EK
+ }, tpm.akHandleCache, ekHandle, credBlob, secretChallenge)
+ if warn, ok := err.(tpm2.Warning); ok && warn.Code == tpm2.RCRetry {
+ time.Sleep(100 * time.Millisecond)
+ continue
+ }
+ return solution, err
+ }
+}
+
+// FlushTransientHandles flushes all sessions and non-persistent handles
+func FlushTransientHandles() error {
+ lock.Lock()
+ defer lock.Unlock()
+ if tpm == nil {
+ return ErrNotInitialized
+ }
+ flushHandleTypes := []tpm2.HandleType{tpm2.HandleTypeTransient, tpm2.HandleTypeLoadedSession, tpm2.HandleTypeSavedSession}
+ for _, handleType := range flushHandleTypes {
+ handles, err := tpm2tools.Handles(tpm.device, handleType)
+ if err != nil {
+ return err
+ }
+ for _, handle := range handles {
+ if err := tpm2.FlushContext(tpm.device, handle); err != nil {
+ return err
+ }
+ }
+ }
+ return nil
+}
+
+// AttestPlatform performs a PCR quote using the AK and returns the quote and its signature
+func AttestPlatform(nonce []byte) ([]byte, []byte, error) {
+ lock.Lock()
+ defer lock.Unlock()
+ if tpm == nil {
+ return []byte{}, []byte{}, ErrNotInitialized
+ }
+ if tpm.akHandleCache == tpmutil.Handle(0) {
+ if err := loadAK(); err != nil {
+ return []byte{}, []byte{}, fmt.Errorf("failed to load AK primary key: %w", err)
+ }
+ }
+ // We only care about SHA256 since SHA1 is weak. This is supported on at least GCE and
+ // Intel / AMD fTPM, which is good enough for now. Alg is null because that would just hash the
+ // nonce, which is dumb.
+ quote, signature, err := tpm2.Quote(tpm.device, tpm.akHandleCache, "", "", nonce, srtmPCRs,
+ tpm2.AlgNull)
+ if err != nil {
+ return []byte{}, []byte{}, fmt.Errorf("failed to quote PCRs: %w", err)
+ }
+ return quote, signature.RSA.Signature, err
+}
+
+// VerifyAttestPlatform verifies a given attestation. You can rely on all data coming back as being
+// from the TPM on which the AK is bound to.
+func VerifyAttestPlatform(nonce, akPub, quote, signature []byte) (*tpm2.AttestationData, error) {
+ hash := crypto.SHA256.New()
+ hash.Write(quote)
+
+ akPubData, err := tpm2.DecodePublic(akPub)
+ if err != nil {
+ return nil, fmt.Errorf("invalid AK: %w", err)
+ }
+ akPublicKey, err := akPubData.Key()
+ if err != nil {
+ return nil, fmt.Errorf("invalid AK: %w", err)
+ }
+ akRSAKey, ok := akPublicKey.(*rsa.PublicKey)
+ if !ok {
+ return nil, errors.New("invalid AK: invalid key type")
+ }
+
+ if err := rsa.VerifyPKCS1v15(akRSAKey, crypto.SHA256, hash.Sum(nil), signature); err != nil {
+ return nil, err
+ }
+
+ quoteData, err := tpm2.DecodeAttestationData(quote)
+ if err != nil {
+ return nil, err
+ }
+ // quoteData.Magic works together with the TPM's Restricted key attribute. If this attribute is set
+ // (which it needs to be for the AK to be considered valid) the TPM will not sign external data
+ // having this prefix with such a key. Only data that originates inside the TPM like quotes and
+ // key certifications can have this prefix and sill be signed by a restricted key. This check
+ // is thus vital, otherwise somebody can just feed the TPM an arbitrary attestation to sign with
+ // its AK and this function will happily accept the forged attestation.
+ if quoteData.Magic != tpmGeneratedValue {
+ return nil, errors.New("invalid TPM quote: data marker for internal data not set - forged attestation")
+ }
+ if quoteData.Type != tpm2.TagAttestQuote {
+ return nil, errors.New("invalid TPM qoute: not a TPM quote")
+ }
+ if !bytes.Equal(quoteData.ExtraData, nonce) {
+ return nil, errors.New("invalid TPM quote: wrong nonce")
+ }
+
+ return quoteData, nil
+}
+
+// GetPCRs returns all SRTM PCRs in-order
+func GetPCRs() ([][]byte, error) {
+ lock.Lock()
+ defer lock.Unlock()
+ if tpm == nil {
+ return [][]byte{}, ErrNotInitialized
+ }
+ pcrs := make([][]byte, numSRTMPCRs)
+
+ // The TPM can (and most do) return partial results. Let's just retry as many times as we have
+ // PCRs since each read should return at least one PCR.
+readLoop:
+ for i := 0; i < numSRTMPCRs; i++ {
+ sel := tpm2.PCRSelection{Hash: tpm2.AlgSHA256}
+ for pcrN := 0; pcrN < numSRTMPCRs; pcrN++ {
+ if len(pcrs[pcrN]) == 0 {
+ sel.PCRs = append(sel.PCRs, pcrN)
+ }
+ }
+
+ readPCRs, err := tpm2.ReadPCRs(tpm.device, sel)
+ if err != nil {
+ return nil, fmt.Errorf("failed to read PCRs: %w", err)
+ }
+
+ for pcrN, pcr := range readPCRs {
+ pcrs[pcrN] = pcr
+ }
+ for _, pcr := range pcrs {
+ // If at least one PCR is still not read, continue
+ if len(pcr) == 0 {
+ continue readLoop
+ }
+ }
+ break
+ }
+
+ return pcrs, nil
+}
+
+// GetMeasurmentLog returns the binary log of all data hashed into PCRs. The result can be parsed by eventlog.
+// As this library currently doesn't support extending PCRs it just returns the log as supplied by the EFI interface.
+func GetMeasurementLog() ([]byte, error) {
+ return ioutil.ReadFile("/sys/kernel/security/tpm0/binary_bios_measurements")
+}