mirror of
https://github.com/edgelesssys/constellation.git
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284 lines
9.7 KiB
Go
284 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 SNP provides types shared by SNP-based attestation implementations.
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// It ensures all issuers provide the same types to the verify command.
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package snp
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import (
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"bytes"
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"crypto/x509"
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"encoding/pem"
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"errors"
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"fmt"
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"github.com/edgelesssys/constellation/v2/internal/attestation"
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"github.com/google/go-sev-guest/abi"
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"github.com/google/go-sev-guest/client"
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"github.com/google/go-sev-guest/kds"
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spb "github.com/google/go-sev-guest/proto/sevsnp"
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"github.com/google/go-sev-guest/verify/trust"
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"github.com/google/go-tpm-tools/proto/attest"
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)
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var errNoPemBlocks = errors.New("no PEM blocks found")
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// Product returns the SEV product info currently supported by Constellation's SNP attestation.
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func Product() *spb.SevProduct {
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// sevProduct is the product info of the SEV platform as reported through CPUID[EAX=1].
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// It may become necessary in the future to differentiate among CSP vendors.
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return &spb.SevProduct{Name: spb.SevProduct_SEV_PRODUCT_MILAN, Stepping: 0} // Milan-B0
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}
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// GetExtendedReport retrieves the extended SNP report from the CVM.
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func GetExtendedReport(reportData [64]byte) (report, certChain []byte, err error) {
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qp, err := client.GetLeveledQuoteProvider()
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if err != nil {
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return nil, nil, fmt.Errorf("getting quote provider: %w", err)
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}
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quote, err := qp.GetRawQuoteAtLevel(reportData, 0)
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if err != nil {
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return nil, nil, fmt.Errorf("getting extended report: %w", err)
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}
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// Parse the report and certificate chain from the quote.
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report = quote
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if len(quote) > abi.ReportSize {
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report = quote[:abi.ReportSize]
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certChain = quote[abi.ReportSize:]
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}
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return report, certChain, nil
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}
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// InstanceInfo contains the necessary information to establish trust in a SNP CVM.
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type InstanceInfo struct {
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// ReportSigner is the PEM-encoded certificate used to validate the attestation report's signature.
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ReportSigner []byte
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// CertChain is the PEM-encoded certificate chain for the attestation report (ASK+ARK).
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// Intermediate key that validates the ReportSigner and root key.
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CertChain []byte
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// AttestationReport is the attestation report from the vTPM (NVRAM) of the CVM.
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AttestationReport []byte
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Azure *AzureInstanceInfo
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GCP *attest.GCEInstanceInfo
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}
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// AzureInstanceInfo contains Azure specific information related to SNP attestation.
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type AzureInstanceInfo struct {
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// RuntimeData is the Azure runtime data from the vTPM (NVRAM) of the CVM.
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RuntimeData []byte
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// MAAToken is the token of the MAA for the attestation report, used as a fallback
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// if the IDKeyDigest cannot be verified.
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MAAToken string
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}
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// addReportSigner parses the reportSigner certificate (VCEK/VLEK) from a and adds it to the attestation proto att.
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// If reportSigner is empty and a VLEK is required, an error is returned.
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// If reportSigner is empty and a VCEK is required, the VCEK is retrieved from AMD KDS.
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func (a *InstanceInfo) addReportSigner(att *spb.Attestation, report *spb.Report, productName string, getter trust.HTTPSGetter, logger attestation.Logger) (abi.ReportSigner, error) {
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// If the VCEK certificate is present, parse it and format it.
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reportSigner, err := a.ParseReportSigner()
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if err != nil {
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logger.Warn(fmt.Sprintf("Error parsing report signer: %v", err))
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}
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signerInfo, err := abi.ParseSignerInfo(report.GetSignerInfo())
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if err != nil {
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return abi.NoneReportSigner, fmt.Errorf("parsing signer info: %w", err)
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}
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switch signerInfo.SigningKey {
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case abi.VlekReportSigner:
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if reportSigner == nil {
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return abi.NoneReportSigner, fmt.Errorf("VLEK certificate required but not present")
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}
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att.CertificateChain.VlekCert = reportSigner.Raw
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case abi.VcekReportSigner:
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var vcekData []byte
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// If no VCEK is present, fetch it from AMD.
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if reportSigner == nil {
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logger.Info("VCEK certificate not present, falling back to retrieving it from AMD KDS")
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vcekURL := kds.VCEKCertURL(productName, report.GetChipId(), kds.TCBVersion(report.GetReportedTcb()))
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vcekData, err = getter.Get(vcekURL)
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if err != nil {
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return abi.NoneReportSigner, fmt.Errorf("retrieving VCEK certificate from AMD KDS: %w", err)
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}
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} else {
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vcekData = reportSigner.Raw
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}
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att.CertificateChain.VcekCert = vcekData
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}
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return signerInfo.SigningKey, nil
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}
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// AttestationWithCerts returns a formatted version of the attestation report and its certificates from the instanceInfo.
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// Certificates are retrieved in the following precedence:
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// 1. ASK from issuer. On Azure: THIM. One AWS: not prefilled. (Go to option 2) On GCP: prefilled.
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// 2. ASK or ARK from fallbackCerts.
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// 3. ASK or ARK from AMD KDS.
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func (a *InstanceInfo) AttestationWithCerts(getter trust.HTTPSGetter,
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fallbackCerts CertificateChain, logger attestation.Logger,
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) (*spb.Attestation, error) {
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report, err := abi.ReportToProto(a.AttestationReport)
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if err != nil {
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return nil, fmt.Errorf("converting report to proto: %w", err)
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}
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productName := kds.ProductLine(Product())
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att := &spb.Attestation{
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Report: report,
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CertificateChain: &spb.CertificateChain{},
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Product: Product(),
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}
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// Add VCEK/VLEK to attestation object.
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signingInfo, err := a.addReportSigner(att, report, productName, getter, logger)
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if err != nil {
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return nil, fmt.Errorf("adding report signer: %w", err)
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}
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// If a certificate chain was pre-fetched by the Issuer, parse it and format it.
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// Make sure to only use the ask, since using an ark from the Issuer would invalidate security guarantees.
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ask, _, err := a.ParseCertChain()
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if err != nil && !errors.Is(err, errNoPemBlocks) {
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logger.Warn(fmt.Sprintf("Error parsing certificate chain: %v", err))
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}
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if ask != nil {
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logger.Info("Using ASK certificate from pre-fetched certificate chain")
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att.CertificateChain.AskCert = ask.Raw
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}
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// If a cached ASK or an ARK from the Constellation config is present, use it.
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if att.CertificateChain.AskCert == nil && fallbackCerts.ask != nil {
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logger.Info("Using cached ASK certificate")
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att.CertificateChain.AskCert = fallbackCerts.ask.Raw
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}
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if fallbackCerts.ark != nil {
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logger.Info("Using cached ARK certificate")
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att.CertificateChain.ArkCert = fallbackCerts.ark.Raw
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}
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// Otherwise, retrieve missing certificates from AMD KDS.
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if att.CertificateChain.AskCert == nil || att.CertificateChain.ArkCert == nil {
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logger.Info(fmt.Sprintf(
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"Certificate chain not fully present (ARK present: %t, ASK present: %t), falling back to retrieving it from AMD KDS",
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(att.CertificateChain.ArkCert != nil),
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(att.CertificateChain.AskCert != nil),
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))
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kdsCertChain, err := trust.GetProductChain(productName, signingInfo, getter)
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if err != nil {
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return nil, fmt.Errorf("retrieving certificate chain from AMD KDS: %w", err)
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}
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if att.CertificateChain.AskCert == nil && kdsCertChain.Ask != nil {
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logger.Info("Using ASK certificate from AMD KDS")
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att.CertificateChain.AskCert = kdsCertChain.Ask.Raw
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}
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if att.CertificateChain.ArkCert == nil && kdsCertChain.Ask != nil {
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logger.Info("Using ARK certificate from AMD KDS")
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att.CertificateChain.ArkCert = kdsCertChain.Ark.Raw
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}
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}
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return att, nil
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}
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// CertificateChain stores an AMD signing key (ASK) and AMD root key (ARK) certificate.
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type CertificateChain struct {
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ask *x509.Certificate
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ark *x509.Certificate
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}
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// NewCertificateChain returns a new CertificateChain with the given ASK and ARK certificates.
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func NewCertificateChain(ask, ark *x509.Certificate) CertificateChain {
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return CertificateChain{
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ask: ask,
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ark: ark,
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}
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}
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// ParseCertChain parses the certificate chain from the instanceInfo into x509-formatted ASK and ARK certificates.
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// If less than 2 certificates are present, only the present certificate is returned.
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// If more than 2 certificates are present, an error is returned.
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func (a *InstanceInfo) ParseCertChain() (ask, ark *x509.Certificate, retErr error) {
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rest := bytes.TrimSpace(a.CertChain)
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i := 1
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var block *pem.Block
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for block, rest = pem.Decode(rest); block != nil; block, rest = pem.Decode(rest) {
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if i > 2 {
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retErr = fmt.Errorf("parse certificate %d: more than 2 certificates in chain", i)
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return
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}
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if block.Type != "CERTIFICATE" {
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retErr = fmt.Errorf("parse certificate %d: expected PEM block type 'CERTIFICATE', got '%s'", i, block.Type)
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return
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}
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cert, err := x509.ParseCertificate(block.Bytes)
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if err != nil {
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retErr = fmt.Errorf("parse certificate %d: %w", i, err)
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return
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}
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// https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/57230.pdf
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// Table 6 and 7
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switch cert.Subject.CommonName {
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case "SEV-Milan", "SEV-VLEK-Milan":
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ask = cert
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case "ARK-Milan":
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ark = cert
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default:
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retErr = fmt.Errorf("parse certificate %d: unexpected subject CN %s", i, cert.Subject.CommonName)
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return
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}
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i++
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}
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switch {
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case i == 1:
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retErr = errNoPemBlocks
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case len(rest) != 0:
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retErr = fmt.Errorf("remaining PEM block is not a valid certificate: %s", rest)
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}
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return
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}
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// ParseReportSigner parses the VCEK/VLEK certificate from the instanceInfo into an x509-formatted certificate.
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// If no certificate is present, nil is returned.
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func (a *InstanceInfo) ParseReportSigner() (*x509.Certificate, error) {
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newlinesTrimmed := bytes.TrimSpace(a.ReportSigner)
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if len(newlinesTrimmed) == 0 {
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// VCEK is not present.
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return nil, nil
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}
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block, rest := pem.Decode(newlinesTrimmed)
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if block == nil {
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return nil, fmt.Errorf("no PEM blocks found")
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}
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if len(rest) != 0 {
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return nil, fmt.Errorf("received more data than expected")
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}
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if block.Type != "CERTIFICATE" {
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return nil, fmt.Errorf("expected PEM block type 'CERTIFICATE', got '%s'", block.Type)
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}
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reportSigner, err := x509.ParseCertificate(block.Bytes)
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if err != nil {
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return nil, fmt.Errorf("parsing VCEK certificate: %w", err)
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}
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return reportSigner, nil
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}
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