mirror of
https://github.com/edgelesssys/constellation.git
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120 lines
3.5 KiB
Go
120 lines
3.5 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 gcp
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import (
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"context"
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"crypto"
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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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compute "cloud.google.com/go/compute/apiv1"
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"cloud.google.com/go/compute/apiv1/computepb"
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"github.com/edgelesssys/constellation/v2/internal/attestation/measurements"
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"github.com/edgelesssys/constellation/v2/internal/attestation/vtpm"
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"github.com/edgelesssys/constellation/v2/internal/variant"
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"github.com/google/go-tpm-tools/proto/attest"
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"github.com/googleapis/gax-go/v2"
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"google.golang.org/api/option"
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)
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const minimumGceVersion = 1
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// Validator for GCP confidential VM attestation.
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type Validator struct {
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variant.GCPSEVES
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*vtpm.Validator
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restClient func(context.Context, ...option.ClientOption) (gcpRestClient, error)
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}
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// NewValidator initializes a new GCP validator with the provided PCR values.
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func NewValidator(pcrs measurements.M, log vtpm.AttestationLogger) *Validator {
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v := &Validator{
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restClient: newInstanceClient,
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}
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v.Validator = vtpm.NewValidator(
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pcrs,
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v.trustedKeyFromGCEAPI,
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validateCVM,
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log,
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)
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return v
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}
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type gcpRestClient interface {
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GetShieldedInstanceIdentity(ctx context.Context, req *computepb.GetShieldedInstanceIdentityInstanceRequest, opts ...gax.CallOption) (*computepb.ShieldedInstanceIdentity, error)
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Close() error
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}
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type instanceClient struct {
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*compute.InstancesClient
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}
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func newInstanceClient(ctx context.Context, opts ...option.ClientOption) (gcpRestClient, error) {
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c, err := compute.NewInstancesRESTClient(ctx, opts...)
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if err != nil {
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return nil, err
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}
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return &instanceClient{c}, nil
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}
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// trustedKeyFromGCEAPI queries the GCE API for a shieldedVM's public signing key.
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// This key can be used to verify attestation statements issued by the VM.
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func (v *Validator) trustedKeyFromGCEAPI(ctx context.Context, attDoc vtpm.AttestationDocument, _ []byte) (crypto.PublicKey, error) {
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client, err := v.restClient(ctx)
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if err != nil {
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return nil, fmt.Errorf("creating GCE client: %w", err)
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}
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defer client.Close()
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var instanceInfo attest.GCEInstanceInfo
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if err := json.Unmarshal(attDoc.InstanceInfo, &instanceInfo); err != nil {
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return nil, err
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}
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instance, err := client.GetShieldedInstanceIdentity(ctx, &computepb.GetShieldedInstanceIdentityInstanceRequest{
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Instance: instanceInfo.GetInstanceName(),
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Project: instanceInfo.GetProjectId(),
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Zone: instanceInfo.GetZone(),
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})
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if err != nil {
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return nil, fmt.Errorf("retrieving VM identity: %w", err)
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}
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if instance.SigningKey == nil || instance.SigningKey.EkPub == nil {
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return nil, fmt.Errorf("received no signing key from GCP API")
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}
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// Parse the signing key return by GetShieldedInstanceIdentity
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block, _ := pem.Decode([]byte(*instance.SigningKey.EkPub))
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if block == nil || block.Type != "PUBLIC KEY" {
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return nil, fmt.Errorf("failed to decode PEM block containing public key")
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}
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return x509.ParsePKIXPublicKey(block.Bytes)
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}
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// validateCVM checks that the machine state represents a GCE AMD-SEV VM.
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func validateCVM(_ vtpm.AttestationDocument, state *attest.MachineState) error {
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gceVersion := state.Platform.GetGceVersion()
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if gceVersion < minimumGceVersion {
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return fmt.Errorf("outdated GCE version: %v (require >= %v)", gceVersion, minimumGceVersion)
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}
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tech := state.Platform.Technology
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wantTech := attest.GCEConfidentialTechnology_AMD_SEV
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if tech != wantTech {
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return fmt.Errorf("unexpected confidential technology: %v (expected: %v)", tech, wantTech)
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}
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return nil
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}
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