mirror of
https://github.com/edgelesssys/constellation.git
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117 lines
3.3 KiB
Go
117 lines
3.3 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
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import (
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"context"
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"crypto/sha512"
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"crypto/x509"
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"encoding/json"
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"encoding/pem"
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"fmt"
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"io"
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"github.com/edgelesssys/constellation/v2/internal/attestation"
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"github.com/edgelesssys/constellation/v2/internal/attestation/snp"
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"github.com/edgelesssys/constellation/v2/internal/attestation/variant"
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"github.com/edgelesssys/constellation/v2/internal/attestation/vtpm"
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"github.com/google/go-sev-guest/abi"
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"github.com/google/go-tpm-tools/client"
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tpmclient "github.com/google/go-tpm-tools/client"
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)
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// Issuer for AWS SNP attestation.
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type Issuer struct {
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variant.AWSSEVSNP
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*vtpm.Issuer
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}
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// NewIssuer creates a SEV-SNP based issuer for AWS.
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func NewIssuer(log attestation.Logger) *Issuer {
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return &Issuer{
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Issuer: vtpm.NewIssuer(
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vtpm.OpenVTPM,
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getAttestationKey,
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getInstanceInfo,
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log,
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),
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}
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}
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// getAttestationKey returns a new attestation key.
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func getAttestationKey(tpm io.ReadWriter) (*tpmclient.Key, error) {
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tpmAk, err := client.AttestationKeyRSA(tpm)
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if err != nil {
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return nil, fmt.Errorf("creating RSA Endorsement key: %w", err)
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}
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return tpmAk, nil
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}
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// getInstanceInfo generates an extended SNP report, i.e. the report and any loaded certificates.
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// Report generation is triggered by sending ioctl syscalls to the SNP guest device, the AMD PSP generates the report.
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// The returned bytes will be written into the attestation document.
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func getInstanceInfo(_ context.Context, tpm io.ReadWriteCloser, _ []byte) ([]byte, error) {
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tpmAk, err := client.AttestationKeyRSA(tpm)
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if err != nil {
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return nil, fmt.Errorf("creating RSA Endorsement key: %w", err)
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}
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encoded, err := x509.MarshalPKIXPublicKey(tpmAk.PublicKey())
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if err != nil {
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return nil, fmt.Errorf("marshalling public key: %w", err)
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}
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akDigest := sha512.Sum512(encoded)
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report, certs, err := snp.GetExtendedReport(akDigest)
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if err != nil {
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return nil, fmt.Errorf("getting extended report: %w", err)
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}
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vlek, err := pemEncodedVLEK(certs)
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if err != nil {
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return nil, fmt.Errorf("parsing vlek: %w", err)
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}
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raw, err := json.Marshal(snp.InstanceInfo{AttestationReport: report, ReportSigner: vlek})
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if err != nil {
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return nil, fmt.Errorf("marshalling instance info: %w", err)
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}
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return raw, nil
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}
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// pemEncodedVLEK takes a marshalled SNP certificate table and returns the PEM-encoded VLEK certificate.
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// AMD documentation on certificate tables can be found in section 4.1.8.1, revision 2.03 "SEV-ES Guest-Hypervisor Communication Block Standardization".
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// https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/56421.pdf
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func pemEncodedVLEK(certs []byte) ([]byte, error) {
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certTable := abi.CertTable{}
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if err := certTable.Unmarshal(certs); err != nil {
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return nil, fmt.Errorf("unmarshalling SNP certificate table: %w", err)
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}
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vlekRaw, err := certTable.GetByGUIDString(abi.VlekGUID)
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if err != nil {
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return nil, fmt.Errorf("getting VLEK certificate: %w", err)
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}
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// An optional check for certificate well-formedness. vlekRaw == cert.Raw.
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cert, err := x509.ParseCertificate(vlekRaw)
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if err != nil {
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return nil, fmt.Errorf("parsing certificate: %w", err)
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}
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certPEM := pem.EncodeToMemory(&pem.Block{
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Type: "CERTIFICATE",
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Bytes: cert.Raw,
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})
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return certPEM, nil
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}
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