mirror of
https://github.com/edgelesssys/constellation.git
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bd63aa3c6b
sed -i '1i/*\nCopyright (c) Edgeless Systems GmbH\n\nSPDX-License-Identifier: AGPL-3.0-only\n*/\n' `grep -rL --include='*.go' 'DO NOT EDIT'` gofumpt -w .
324 lines
12 KiB
Go
324 lines
12 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 azure
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import (
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"bytes"
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"crypto"
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"crypto/sha256"
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"crypto/x509"
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"encoding/asn1"
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"encoding/base64"
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"encoding/binary"
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"encoding/json"
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"errors"
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"fmt"
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"math/big"
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"github.com/edgelesssys/constellation/internal/attestation/vtpm"
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internalCrypto "github.com/edgelesssys/constellation/internal/crypto"
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"github.com/edgelesssys/constellation/internal/oid"
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"github.com/google/go-tpm/tpm2"
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)
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// AMD root key. Received from the AMD Key Distribution System API (KDS).
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const arkPEM = "-----BEGIN CERTIFICATE-----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\nAFZEAwoKCQ==\n-----END CERTIFICATE-----\n"
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// Validator for Azure confidential VM attestation.
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type Validator struct {
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oid.Azure
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*vtpm.Validator
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}
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// NewValidator initializes a new Azure validator with the provided PCR values.
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func NewValidator(pcrs map[uint32][]byte, enforcedPCRs []uint32, idkeydigest []byte, enforceIdKeyDigest bool, log vtpm.WarnLogger) *Validator {
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return &Validator{
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Validator: vtpm.NewValidator(
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pcrs,
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enforcedPCRs,
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trustedKeyFromSNP(&azureInstanceInfo{}, idkeydigest, enforceIdKeyDigest, log),
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validateAzureCVM,
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vtpm.VerifyPKCS1v15,
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log,
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),
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}
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}
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type signatureError struct {
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innerError error
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}
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func (e *signatureError) Unwrap() error {
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return e.innerError
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}
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func (e *signatureError) Error() string {
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return fmt.Sprintf("signature validation failed: %v", e.innerError)
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}
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type askError struct {
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innerError error
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}
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func (e *askError) Unwrap() error {
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return e.innerError
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}
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func (e *askError) Error() string {
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return fmt.Sprintf("validating ASK: %v", e.innerError)
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}
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type vcekError struct {
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innerError error
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}
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func (e *vcekError) Unwrap() error {
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return e.innerError
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}
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func (e *vcekError) Error() string {
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return fmt.Sprintf("validating VCEK: %v", e.innerError)
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}
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type idkeyError struct {
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expectedValue []byte
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}
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func (e *idkeyError) Unwrap() error {
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return nil
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}
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func (e *idkeyError) Error() string {
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return fmt.Sprintf("configured idkeydigest does not match reported idkeydigest: %x", e.expectedValue)
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}
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// trustedKeyFromSNP establishes trust in the given public key.
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// It does so by verifying the SNP attestation statement in instanceInfo.
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func trustedKeyFromSNP(hclAk HCLAkValidator, idkeydigest []byte, enforceIdKeyDigest bool, log vtpm.WarnLogger) func(akPub, instanceInfoRaw []byte) (crypto.PublicKey, error) {
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return func(akPub, instanceInfoRaw []byte) (crypto.PublicKey, error) {
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var instanceInfo azureInstanceInfo
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if err := json.Unmarshal(instanceInfoRaw, &instanceInfo); err != nil {
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return nil, fmt.Errorf("unmarshalling instanceInfoRaw: %w", err)
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}
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report, err := newSNPReportFromBytes(instanceInfo.AttestationReport)
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if err != nil {
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return nil, fmt.Errorf("parsing attestation report: %w", err)
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}
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vcek, err := validateVCEK(instanceInfo.Vcek, instanceInfo.CertChain)
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if err != nil {
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return nil, fmt.Errorf("validating VCEK: %w", err)
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}
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if err = validateSNPReport(vcek, idkeydigest, enforceIdKeyDigest, report, log); err != nil {
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return nil, fmt.Errorf("validating SNP report: %w", err)
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}
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pubArea, err := tpm2.DecodePublic(akPub)
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if err != nil {
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return nil, err
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}
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if err = hclAk.validateAk(instanceInfo.RuntimeData, report.ReportData[:], pubArea.RSAParameters); err != nil {
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return nil, fmt.Errorf("validating HCLAkPub: %w", err)
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}
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return pubArea.Key()
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}
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}
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func reverseEndian(b []byte) {
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for i := 0; i < len(b)/2; i++ {
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b[i], b[len(b)-i-1] = b[len(b)-i-1], b[i]
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}
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}
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// validateAzureCVM is a stub, since SEV-SNP attestation is already verified in trustedKeyFromSNP().
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func validateAzureCVM(attestation vtpm.AttestationDocument) error {
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return nil
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}
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func newSNPReportFromBytes(reportRaw []byte) (snpAttestationReport, error) {
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var report snpAttestationReport
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if err := binary.Read(bytes.NewReader(reportRaw), binary.LittleEndian, &report); err != nil {
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return snpAttestationReport{}, fmt.Errorf("reading attestation report: %w", err)
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}
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return report, nil
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}
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// validateVCEK takes the PEM-encoded X509 certificate VCEK, ASK and ARK and verifies the integrity of the chain.
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// ARK (hardcoded) validates ASK (cloud metadata API) validates VCEK (cloud metadata API).
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func validateVCEK(vcekRaw []byte, certChain []byte) (*x509.Certificate, error) {
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vcek, err := internalCrypto.PemToX509Cert(vcekRaw)
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if err != nil {
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return nil, fmt.Errorf("loading vcek: %w", err)
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}
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ark, err := internalCrypto.PemToX509Cert([]byte(arkPEM))
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if err != nil {
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return nil, fmt.Errorf("loading arkPEM: %w", err)
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}
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// certChain includes two PEM encoded certs. The ASK and the ARK, in that order.
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ask, err := internalCrypto.PemToX509Cert(certChain)
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if err != nil {
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return nil, fmt.Errorf("loading askPEM: %w", err)
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}
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if err = ask.CheckSignatureFrom(ark); err != nil {
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return nil, &askError{err}
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}
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if err = vcek.CheckSignatureFrom(ask); err != nil {
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return nil, &vcekError{err}
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}
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return vcek, nil
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}
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func validateSNPReport(cert *x509.Certificate, expectedIdKeyDigest []byte, enforceIdKeyDigest bool, report snpAttestationReport, log vtpm.WarnLogger) error {
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sig_r := report.Signature.R[:]
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sig_s := report.Signature.S[:]
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// Table 107 in https://www.amd.com/system/files/TechDocs/56860.pdf mentions little endian signature components.
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// They come out of the certificate as big endian.
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reverseEndian(sig_r)
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reverseEndian(sig_s)
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r := new(big.Int).SetBytes(sig_r)
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s := new(big.Int).SetBytes(sig_s)
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sequence := ecdsaSig{r, s}
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sigEncoded, err := asn1.Marshal(sequence)
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if err != nil {
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return fmt.Errorf("marshalling ecdsa signature: %w", err)
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}
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buf := new(bytes.Buffer)
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if err = binary.Write(buf, binary.LittleEndian, report); err != nil {
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return fmt.Errorf("writing report to buf: %w", err)
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}
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// signature is only calculated from 0x0 to 0x2a0
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if err := cert.CheckSignature(x509.ECDSAWithSHA384, buf.Bytes()[:0x2a0], sigEncoded); err != nil {
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return &signatureError{err}
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}
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if !bytes.Equal(expectedIdKeyDigest, report.IdKeyDigest[:]) {
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if enforceIdKeyDigest {
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return &idkeyError{report.IdKeyDigest[:]}
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}
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if log != nil {
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log.Warnf("Encountered different than configured idkeydigest value: %x.\n", report.IdKeyDigest[:])
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}
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}
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return nil
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}
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type azureInstanceInfo struct {
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Vcek []byte
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CertChain []byte
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AttestationReport []byte
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RuntimeData []byte
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}
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// validateAk validates that the attestation key from the TPM is trustworthy. The steps are:
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// 1. runtime data read from the TPM has the same sha256 digest as reported in `report_data` of the SNP report.
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// 2. modulus reported in runtime data matches modulus from key at idx 0x81000003.
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// 3. exponent reported in runtime data matches exponent from key at idx 0x81000003.
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// The function is currently tested manually on a Azure Ubuntu CVM.
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func (a *azureInstanceInfo) validateAk(runtimeDataRaw []byte, reportData []byte, rsaParameters *tpm2.RSAParams) error {
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var runtimeData runtimeData
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if err := json.Unmarshal(runtimeDataRaw, &runtimeData); err != nil {
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return fmt.Errorf("unmarshalling json: %w", err)
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}
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sum := sha256.Sum256(runtimeDataRaw)
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if !bytes.Equal(sum[:], reportData[:len(sum)]) {
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return errors.New("unexpected runtimeData digest in TPM")
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}
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if len(runtimeData.Keys) < 1 {
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return errors.New("did not receive any keys in runtime data")
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}
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rawN, err := base64.RawURLEncoding.DecodeString(runtimeData.Keys[0].N)
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if err != nil {
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return err
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}
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if !bytes.Equal(rawN, rsaParameters.ModulusRaw) {
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return fmt.Errorf("unexpected modulus value in TPM")
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}
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rawE, err := base64.RawURLEncoding.DecodeString(runtimeData.Keys[0].E)
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if err != nil {
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return err
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}
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paddedRawE := make([]byte, 4)
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copy(paddedRawE, rawE)
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exponent := binary.LittleEndian.Uint32(paddedRawE)
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// According to this comment [1] the TPM uses "0" to represent the default exponent "65537".
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// The go tpm library also reports the exponent as 0. Thus we have to handle it specially.
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// [1] https://github.com/tpm2-software/tpm2-tools/pull/1973#issue-596685005
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if !((exponent == 65537 && rsaParameters.ExponentRaw == 0) || exponent == rsaParameters.ExponentRaw) {
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return fmt.Errorf("unexpected N value in TPM")
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}
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return nil
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}
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type HCLAkValidator interface {
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validateAk(runtimeDataRaw []byte, reportData []byte, rsaParameters *tpm2.RSAParams) error
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}
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type snpSignature struct {
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R [72]byte
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S [72]byte
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Reserved [512 - 144]byte
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}
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// Reference: https://github.com/AMDESE/sev-guest/blob/main/include/attestation.h
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type snpAttestationReport struct {
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Version uint32 /* 0x000 */
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GuestSvn uint32 /* 0x004 */
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Policy uint64 /* 0x008 */
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FamilyId [16]byte /* 0x010 */
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ImageId [16]byte /* 0x020 */
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Vmpl uint32 /* 0x030 */
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SignatureAlgo uint32 /* 0x034 */
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PlatformVersion uint64 /* 0x038 */
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PlatformInfo uint64 /* 0x040 */
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Flags uint32 /* 0x048 */
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Reserved0 uint32 /* 0x04C */
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ReportData [64]byte /* 0x050 */
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Measurement [48]byte /* 0x090 */
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HostData [32]byte /* 0x0C0 */
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IdKeyDigest [48]byte /* 0x0E0 */
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AuthorKeyDigest [48]byte /* 0x110 */
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ReportId [32]byte /* 0x140 */
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ReportIdMa [32]byte /* 0x160 */
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ReportedTcb uint64 /* 0x180 */
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Reserved1 [24]byte /* 0x188 */
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ChipId [64]byte /* 0x1A0 */
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Reserved2 [192]byte /* 0x1E0 */
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Signature snpSignature /* 0x2A0 */
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}
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type ecdsaSig struct {
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R, S *big.Int
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}
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type akPub struct {
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E string
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N string
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}
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type runtimeData struct {
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Keys []akPub
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}
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