constellation/internal/attestation/aws/validator.go

101 lines
3.0 KiB
Go
Raw Normal View History

/*
Copyright (c) Edgeless Systems GmbH
SPDX-License-Identifier: AGPL-3.0-only
*/
package aws
import (
"context"
"crypto"
"encoding/json"
"fmt"
awsConfig "github.com/aws/aws-sdk-go-v2/config"
"github.com/aws/aws-sdk-go-v2/feature/ec2/imds"
"github.com/aws/aws-sdk-go-v2/service/ec2"
"github.com/edgelesssys/constellation/v2/internal/attestation/measurements"
"github.com/edgelesssys/constellation/v2/internal/attestation/vtpm"
2022-09-21 07:47:57 -04:00
"github.com/edgelesssys/constellation/v2/internal/oid"
"github.com/google/go-tpm-tools/proto/attest"
"github.com/google/go-tpm/tpm2"
)
// Validator for AWS TPM attestation.
type Validator struct {
oid.AWSNitroTPM
*vtpm.Validator
getDescribeClient func(context.Context, string) (awsMetadataAPI, error)
}
// NewValidator create a new Validator structure and returns it.
func NewValidator(pcrs measurements.M, log vtpm.AttestationLogger) *Validator {
v := &Validator{}
v.Validator = vtpm.NewValidator(
pcrs,
getTrustedKey,
v.tpmEnabled,
log,
)
v.getDescribeClient = getEC2Client
return v
}
// getTrustedKeys return the public area of the provides attestation key.
// Normally, here the trust of this key should be verified, but currently AWS does not provide this feature.
func getTrustedKey(akPub []byte, _ []byte) (crypto.PublicKey, error) {
// Copied from https://github.com/edgelesssys/constellation/blob/main/internal/attestation/qemu/validator.go
pubArea, err := tpm2.DecodePublic(akPub)
if err != nil {
return nil, err
}
return pubArea.Key()
}
// tpmEnabled verifies if the virtual machine has the tpm2.0 feature enabled.
func (v *Validator) tpmEnabled(attestation vtpm.AttestationDocument, _ *attest.MachineState) error {
// https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/verify-nitrotpm-support-on-ami.html
// 1. Get the vm's ami (from IdentiTyDocument.imageId)
// 2. Check the value of key "TpmSupport": {"Value": "v2.0"}"
ctx := context.Background()
idDocument := imds.InstanceIdentityDocument{}
err := json.Unmarshal(attestation.InstanceInfo, &idDocument)
if err != nil {
return err
}
imageID := idDocument.ImageID
client, err := v.getDescribeClient(ctx, idDocument.Region)
if err != nil {
return err
}
// Currently, there seems to be a problem with retrieving image attributes directly.
// Alternatively, parse it from the general output.
imageOutput, err := client.DescribeImages(ctx, &ec2.DescribeImagesInput{ImageIds: []string{imageID}})
if err != nil {
return err
}
if imageOutput.Images[0].TpmSupport == "v2.0" {
return nil
}
return fmt.Errorf("iam image %s does not support TPM v2.0", imageID)
}
func getEC2Client(ctx context.Context, region string) (awsMetadataAPI, error) {
client, err := awsConfig.LoadDefaultConfig(ctx, awsConfig.WithRegion(region))
if err != nil {
return nil, err
}
return ec2.NewFromConfig(client), nil
}
type awsMetadataAPI interface {
DescribeImages(ctx context.Context, params *ec2.DescribeImagesInput, optFns ...func(*ec2.Options)) (*ec2.DescribeImagesOutput, error)
}