mirror of
https://github.com/edgelesssys/constellation.git
synced 2024-12-28 08:59:34 -05:00
301 lines
9.7 KiB
Go
301 lines
9.7 KiB
Go
/*
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Copyright (c) Edgeless Systems GmbH
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SPDX-License-Identifier: AGPL-3.0-only
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*/
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package vtpm
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import (
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"bytes"
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"context"
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"crypto"
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"crypto/sha256"
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"encoding/json"
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"fmt"
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"io"
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tpmClient "github.com/google/go-tpm-tools/client"
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"github.com/google/go-tpm-tools/proto/attest"
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tpmProto "github.com/google/go-tpm-tools/proto/tpm"
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tpmServer "github.com/google/go-tpm-tools/server"
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"github.com/google/go-tpm/tpm2"
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"github.com/edgelesssys/constellation/v2/internal/attestation/measurements"
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)
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var (
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// AzurePCRSelection are the PCR values verified for Azure Constellations.
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// PCR[0] is excluded due to changing rarely, but unpredictably.
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// PCR[6] is excluded due to being different for any 2 VMs. See: https://trustedcomputinggroup.org/wp-content/uploads/TCG_PCClient_PFP_r1p05_v23_pub.pdf#%5B%7B%22num%22%3A157%2C%22gen%22%3A0%7D%2C%7B%22name%22%3A%22XYZ%22%7D%2C33%2C400%2C0%5D
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// PCR[10] is excluded since its value is derived from a digest of PCR[0-7]. See: https://sourceforge.net/p/linux-ima/wiki/Home/#ima-measurement-list
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AzurePCRSelection = tpm2.PCRSelection{
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Hash: tpm2.AlgSHA256,
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PCRs: []int{1, 2, 3, 4, 5, 7, 8, 9, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23},
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}
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// GCPPCRSelection are the PCR values verified for GCP Constellations.
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// On GCP firmware and other host controlled systems are static. This results in the same PCRs for any 2 VMs using the same image.
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GCPPCRSelection = tpmClient.FullPcrSel(tpm2.AlgSHA256)
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// AWSPCRSelection are the PCR values verified for AWS based Constellations.
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// PCR[1] is excluded. See: https://trustedcomputinggroup.org/wp-content/uploads/TCG_PCClient_PFP_r1p05_v23_pub.pdf#%5B%7B%22num%22:157,%22gen%22:0%7D,%7B%22name%22:%22XYZ%22%7D,33,400,0%5D
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// PCR[10] is excluded since its value is derived from a digest of PCR[0-7]. See: https://sourceforge.net/p/linux-ima/wiki/Home/#ima-measurement-list
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AWSPCRSelection = tpm2.PCRSelection{
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Hash: tpm2.AlgSHA256,
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PCRs: []int{0, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23},
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}
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// QEMUPCRSelection are the PCR values verified for QEMU based Constellations.
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// PCR[1] is excluded. See: https://trustedcomputinggroup.org/wp-content/uploads/TCG_PCClient_PFP_r1p05_v23_pub.pdf#%5B%7B%22num%22:157,%22gen%22:0%7D,%7B%22name%22:%22XYZ%22%7D,33,400,0%5D
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// PCR[10] is excluded since its value is derived from a digest of PCR[0-7]. See: https://sourceforge.net/p/linux-ima/wiki/Home/#ima-measurement-list
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QEMUPCRSelection = tpm2.PCRSelection{
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Hash: tpm2.AlgSHA256,
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PCRs: []int{0, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23},
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}
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)
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type (
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// GetTPMAttestationKey loads a TPM key to perform attestation.
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GetTPMAttestationKey func(tpm io.ReadWriter) (*tpmClient.Key, error)
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// GetTPMTrustedAttestationPublicKey verifies and returns the attestation public key.
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GetTPMTrustedAttestationPublicKey func(context.Context, AttestationDocument, []byte) (crypto.PublicKey, error)
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// GetInstanceInfo returns VM metdata.
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GetInstanceInfo func(ctx context.Context, tpm io.ReadWriteCloser, extraData []byte) ([]byte, error)
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// ValidateCVM validates confidential computing capabilities of the instance issuing the attestation.
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ValidateCVM func(attestation AttestationDocument, state *attest.MachineState) error
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)
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// AttestationLogger is a logger used to print warnings and infos during attestation validation.
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type AttestationLogger interface {
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Infof(format string, args ...any)
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Warnf(format string, args ...any)
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}
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// AttestationDocument contains the TPM attestation with signed user data.
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type AttestationDocument struct {
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// Attestation contains the TPM event log, PCR values and quotes, and public key of the key used to sign the attestation.
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Attestation *attest.Attestation
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// InstanceInfo is used to verify the provided public key.
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InstanceInfo []byte
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// arbitrary data, quoted by the TPM.
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UserData []byte
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}
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// Issuer handles issuing of TPM based attestation documents.
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type Issuer struct {
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openTPM TPMOpenFunc
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getAttestationKey GetTPMAttestationKey
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getInstanceInfo GetInstanceInfo
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log AttestationLogger
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}
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// NewIssuer returns a new Issuer.
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func NewIssuer(
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openTPM TPMOpenFunc, getAttestationKey GetTPMAttestationKey,
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getInstanceInfo GetInstanceInfo, log AttestationLogger,
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) *Issuer {
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if log == nil {
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log = &nopAttestationLogger{}
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}
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return &Issuer{
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openTPM: openTPM,
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getAttestationKey: getAttestationKey,
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getInstanceInfo: getInstanceInfo,
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log: log,
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}
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}
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// Issue generates an attestation document using a TPM.
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func (i *Issuer) Issue(userData []byte, nonce []byte) (res []byte, err error) {
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i.log.Infof("Issuing attestation statement")
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defer func() {
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if err != nil {
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i.log.Warnf("Failed to issue attestation statement: %s", err)
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}
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}()
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tpm, err := i.openTPM()
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if err != nil {
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return nil, fmt.Errorf("opening TPM: %w", err)
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}
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defer tpm.Close()
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// Load the TPM's attestation key
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aK, err := i.getAttestationKey(tpm)
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if err != nil {
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return nil, fmt.Errorf("loading attestation key: %w", err)
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}
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defer aK.Close()
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// Create an attestation using the loaded key
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extraData := makeExtraData(userData, nonce)
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tpmAttestation, err := aK.Attest(tpmClient.AttestOpts{Nonce: extraData})
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if err != nil {
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return nil, fmt.Errorf("creating attestation: %w", err)
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}
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// Fetch instance info of the VM
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instanceInfo, err := i.getInstanceInfo(context.TODO(), tpm, extraData) // TODO(daniel-weisse): update Issue/Validate to use context
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if err != nil {
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return nil, fmt.Errorf("fetching instance info: %w", err)
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}
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attDoc := AttestationDocument{
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Attestation: tpmAttestation,
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InstanceInfo: instanceInfo,
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UserData: userData,
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}
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rawAttDoc, err := json.Marshal(attDoc)
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if err != nil {
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return nil, fmt.Errorf("marshaling attestation document: %w", err)
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}
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i.log.Infof("Successfully issued attestation statement")
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return rawAttDoc, nil
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}
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// Validator handles validation of TPM based attestation.
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type Validator struct {
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expected measurements.M
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getTrustedKey GetTPMTrustedAttestationPublicKey
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validateCVM ValidateCVM
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log AttestationLogger
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}
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// NewValidator returns a new Validator.
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func NewValidator(expected measurements.M, getTrustedKey GetTPMTrustedAttestationPublicKey,
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validateCVM ValidateCVM, log AttestationLogger,
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) *Validator {
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if log == nil {
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log = &nopAttestationLogger{}
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}
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return &Validator{
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expected: expected,
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getTrustedKey: getTrustedKey,
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validateCVM: validateCVM,
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log: log,
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}
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}
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// Validate a TPM based attestation.
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func (v *Validator) Validate(attDocRaw []byte, nonce []byte) (userData []byte, err error) {
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v.log.Infof("Validating attestation document")
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defer func() {
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if err != nil {
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v.log.Warnf("Failed to validate attestation document: %s", err)
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}
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}()
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var attDoc AttestationDocument
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if err := json.Unmarshal(attDocRaw, &attDoc); err != nil {
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return nil, fmt.Errorf("unmarshaling TPM attestation document: %w", err)
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}
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extraData := makeExtraData(attDoc.UserData, nonce)
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// Verify and retrieve the trusted attestation public key using the provided instance info
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aKP, err := v.getTrustedKey(context.TODO(), attDoc, extraData)
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if err != nil {
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return nil, fmt.Errorf("validating attestation public key: %w", err)
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}
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// Verify the TPM attestation
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state, err := tpmServer.VerifyAttestation(
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attDoc.Attestation,
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tpmServer.VerifyOpts{
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Nonce: extraData,
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TrustedAKs: []crypto.PublicKey{aKP},
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AllowSHA1: false,
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},
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)
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if err != nil {
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return nil, fmt.Errorf("verifying attestation document: %w", err)
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}
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// Validate confidential computing capabilities of the VM
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if err := v.validateCVM(attDoc, state); err != nil {
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return nil, fmt.Errorf("verifying VM confidential computing capabilities: %w", err)
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}
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// Verify PCRs
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quoteIdx, err := GetSHA256QuoteIndex(attDoc.Attestation.Quotes)
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if err != nil {
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return nil, err
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}
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for idx, pcr := range v.expected {
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if !bytes.Equal(pcr.Expected[:], attDoc.Attestation.Quotes[quoteIdx].Pcrs.Pcrs[idx]) {
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if !pcr.ValidationOpt {
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return nil, fmt.Errorf("untrusted PCR value at PCR index %d", idx)
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}
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v.log.Warnf("Encountered untrusted PCR value at index %d", idx)
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}
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}
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v.log.Infof("Successfully validated attestation document")
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return attDoc.UserData, nil
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}
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// GetSHA256QuoteIndex performs safety checks and returns the index for SHA256 PCR quotes.
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func GetSHA256QuoteIndex(quotes []*tpmProto.Quote) (int, error) {
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if len(quotes) == 0 {
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return 0, fmt.Errorf("attestation is missing quotes")
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}
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for idx, quote := range quotes {
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if quote == nil {
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return 0, fmt.Errorf("quote is nil")
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}
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if quote.Pcrs == nil {
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return 0, fmt.Errorf("no PCR data in attestation")
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}
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if quote.Pcrs.Hash == tpmProto.HashAlgo_SHA256 {
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return idx, nil
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}
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}
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return 0, fmt.Errorf("attestation did not include SHA256 hashed PCRs")
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}
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// GetSelectedMeasurements returns a map of Measurments for the PCRs in selection.
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func GetSelectedMeasurements(open TPMOpenFunc, selection tpm2.PCRSelection) (measurements.M, error) {
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tpm, err := open()
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if err != nil {
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return nil, err
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}
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defer tpm.Close()
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pcrList, err := tpmClient.ReadPCRs(tpm, selection)
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if err != nil {
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return nil, err
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}
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m := make(measurements.M)
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for i, pcr := range pcrList.Pcrs {
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if len(pcr) != 32 {
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return nil, fmt.Errorf("invalid measurement: invalid length: %d", len(pcr))
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}
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m[i] = measurements.Measurement{
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Expected: *(*[32]byte)(pcr),
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}
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}
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return m, nil
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}
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func makeExtraData(userData []byte, nonce []byte) []byte {
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data := append([]byte{}, userData...)
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data = append(data, nonce...)
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digest := sha256.Sum256(data)
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return digest[:]
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}
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// nopAttestationLogger is a no-op implementation of AttestationLogger.
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type nopAttestationLogger struct{}
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// Infof is a no-op.
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func (nopAttestationLogger) Infof(string, ...interface{}) {}
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// Warnf is a no-op.
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func (nopAttestationLogger) Warnf(string, ...interface{}) {}
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