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https://github.com/edgelesssys/constellation.git
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9765003298
* Print measurements as ordered list during verify * Fix missing safety check in AWS attestation validation --------- Signed-off-by: Daniel Weiße <dw@edgeless.systems>
108 lines
3.3 KiB
Go
108 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"
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"encoding/json"
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"fmt"
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awsConfig "github.com/aws/aws-sdk-go-v2/config"
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"github.com/aws/aws-sdk-go-v2/feature/ec2/imds"
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"github.com/aws/aws-sdk-go-v2/service/ec2"
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"github.com/edgelesssys/constellation/v2/internal/attestation"
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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/edgelesssys/constellation/v2/internal/config"
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"github.com/google/go-tpm-tools/proto/attest"
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"github.com/google/go-tpm/legacy/tpm2"
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)
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// Validator for AWS TPM attestation.
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type Validator struct {
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variant.AWSSEVSNP
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*vtpm.Validator
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getDescribeClient func(context.Context, string) (awsMetadataAPI, error)
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}
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// NewValidator create a new Validator structure and returns it.
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func NewValidator(cfg *config.AWSSEVSNP, log attestation.Logger) *Validator {
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v := &Validator{}
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v.Validator = vtpm.NewValidator(
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cfg.Measurements,
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getTrustedKey,
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v.tpmEnabled,
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log,
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)
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v.getDescribeClient = getEC2Client
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return v
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}
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// getTrustedKeys return the public area of the provides attestation key.
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// Normally, here the trust of this key should be verified, but currently AWS does not provide this feature.
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func getTrustedKey(_ context.Context, attDoc vtpm.AttestationDocument, _ []byte) (crypto.PublicKey, error) {
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// Copied from https://github.com/edgelesssys/constellation/blob/main/internal/attestation/qemu/validator.go
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pubArea, err := tpm2.DecodePublic(attDoc.Attestation.AkPub)
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if err != nil {
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return nil, err
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}
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return pubArea.Key()
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}
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// tpmEnabled verifies if the virtual machine has the tpm2.0 feature enabled.
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func (v *Validator) tpmEnabled(attestation vtpm.AttestationDocument, _ *attest.MachineState) error {
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// https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/verify-nitrotpm-support-on-ami.html
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// 1. Get the vm's ami (from IdentiTyDocument.imageId)
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// 2. Check the value of key "TpmSupport": {"Value": "v2.0"}"
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ctx := context.Background()
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idDocument := imds.InstanceIdentityDocument{}
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err := json.Unmarshal(attestation.InstanceInfo, &idDocument)
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if err != nil {
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return err
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}
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imageID := idDocument.ImageID
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client, err := v.getDescribeClient(ctx, idDocument.Region)
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if err != nil {
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return err
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}
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// Currently, there seems to be a problem with retrieving image attributes directly.
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// Alternatively, parse it from the general output.
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imageOutput, err := client.DescribeImages(ctx, &ec2.DescribeImagesInput{ImageIds: []string{imageID}})
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if err != nil {
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return err
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}
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if len(imageOutput.Images) == 0 {
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return fmt.Errorf("aws image %s not found", imageID)
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}
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if len(imageOutput.Images) > 1 {
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return fmt.Errorf("found multiple image references for image ID %s", imageID)
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}
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if imageOutput.Images[0].TpmSupport == "v2.0" {
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return nil
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}
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return fmt.Errorf("aws image %s does not support TPM v2.0", imageID)
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}
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func getEC2Client(ctx context.Context, region string) (awsMetadataAPI, error) {
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client, err := awsConfig.LoadDefaultConfig(ctx, awsConfig.WithRegion(region))
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if err != nil {
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return nil, err
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}
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return ec2.NewFromConfig(client), nil
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}
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type awsMetadataAPI interface {
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DescribeImages(ctx context.Context, params *ec2.DescribeImagesInput, optFns ...func(*ec2.Options)) (*ec2.DescribeImagesOutput, error)
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}
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