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generate.go
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generate.go
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/*
Copyright (c) Edgeless Systems GmbH
SPDX-License-Identifier: AGPL-3.0-only
*/
package main
import (
"bytes"
"context"
"fmt"
"go/ast"
"go/parser"
"go/printer"
"go/token"
"log"
"net/http"
"net/url"
"os"
"path"
"sort"
"strconv"
"strings"
"github.com/edgelesssys/constellation/v2/internal/api/versionsapi"
"github.com/edgelesssys/constellation/v2/internal/attestation/measurements"
"github.com/edgelesssys/constellation/v2/internal/attestation/variant"
"github.com/edgelesssys/constellation/v2/internal/cloud/cloudprovider"
"github.com/edgelesssys/constellation/v2/internal/constants"
"github.com/edgelesssys/constellation/v2/internal/sigstore"
"github.com/edgelesssys/constellation/v2/internal/sigstore/keyselect"
"golang.org/x/tools/go/ast/astutil"
)
// this tool is used to generate hardcoded measurements for the enterprise build.
// Measurements are embedded in the constellation cli.
func main() {
const imageFilePath = "../../config/image_enterprise.go"
defaultImage, err := imageVersionFromFile(imageFilePath)
if err != nil {
log.Fatalf("error parsing image version from %s: %s", imageFilePath, err)
}
log.Printf("Generating measurements for %s\n", defaultImage)
const outFilePath = "./measurements_enterprise.go"
ctx := context.Background()
fset := token.NewFileSet()
outFile, err := parser.ParseFile(fset, outFilePath, nil, parser.ParseComments)
if err != nil {
log.Fatal(err)
}
rekor, err := sigstore.NewRekor()
if err != nil {
log.Fatal(err)
}
var returnStmtCtr int
newFile := astutil.Apply(outFile, func(cursor *astutil.Cursor) bool {
n := cursor.Node()
// find all variables of the form <provider>_<variant> and replace them with updated measurements
// see ../measurements_enterprise.go for an example
if clause, ok := n.(*ast.ValueSpec); ok && len(clause.Names) == 1 && len(clause.Values) == 1 {
varName := clause.Names[0].Name
_, ok := clause.Values[0].(*ast.CompositeLit)
if !ok {
return true
}
nameParts := strings.Split(varName, "_")
if len(nameParts) != 2 {
return true
}
provider := cloudprovider.FromString(nameParts[0])
variant, err := attestationVariantFromGoIdentifier(nameParts[1])
if err != nil {
log.Fatalf("error parsing variant %s: %s", nameParts[1], err)
}
log.Println("Found", variant)
returnStmtCtr++
// retrieve and validate measurements for the given CSP and image
measuremnts := mustGetMeasurements(ctx, rekor, provider, variant, defaultImage)
// replace the return statement with a composite literal containing the validated measurements
clause.Values[0] = measurementsCompositeLiteral(measuremnts)
}
return true
}, nil,
)
if returnStmtCtr == 0 {
log.Fatal("no measurements updated")
}
var buf bytes.Buffer
printConfig := printer.Config{Mode: printer.UseSpaces | printer.TabIndent, Tabwidth: 8}
if err = printConfig.Fprint(&buf, fset, newFile); err != nil {
log.Fatalf("error formatting file %s: %s", outFilePath, err)
}
if err := os.WriteFile(outFilePath, buf.Bytes(), 0o644); err != nil {
log.Fatalf("error writing file %s: %s", outFilePath, err)
}
log.Println("Successfully generated hashes.")
}
// mustGetMeasurements fetches the measurements for the given image and CSP and verifies them.
func mustGetMeasurements(ctx context.Context, verifier rekorVerifier, provider cloudprovider.Provider, attestationVariant variant.Variant, image string) measurements.M {
measurementsURL, err := measurementURL(image, constants.CDNMeasurementsFile)
if err != nil {
panic(err)
}
signatureURL, err := measurementURL(image, constants.CDNMeasurementsSignature)
if err != nil {
panic(err)
}
imageVersion, err := versionsapi.NewVersionFromShortPath(image, versionsapi.VersionKindImage)
if err != nil {
panic(err)
}
publicKey, err := keyselect.CosignPublicKeyForVersion(imageVersion)
if err != nil {
panic(fmt.Errorf("getting public key: %w", err))
}
cosignVerifier, err := sigstore.NewCosignVerifier(publicKey)
if err != nil {
panic(fmt.Errorf("creating cosign verifier: %w", err))
}
log.Println("Fetching measurements from", measurementsURL, "and signature from", signatureURL)
var fetchedMeasurements measurements.M
hash, err := fetchedMeasurements.FetchAndVerify(
ctx, http.DefaultClient, cosignVerifier,
measurementsURL,
signatureURL,
imageVersion,
provider,
attestationVariant,
)
if err != nil {
panic(err)
}
if err := sigstore.VerifyWithRekor(ctx, publicKey, verifier, hash); err != nil {
panic(err)
}
return fetchedMeasurements
}
// measurementURL returns the URL for the measurements file for the given image and CSP.
func measurementURL(image, file string) (*url.URL, error) {
version, err := versionsapi.NewVersionFromShortPath(image, versionsapi.VersionKindImage)
if err != nil {
return nil, fmt.Errorf("parsing image name: %w", err)
}
return url.Parse(
version.ArtifactsURL(versionsapi.APIV2) + path.Join("/image", file),
)
}
// byteArrayCompositeLit returns a *ast.CompositeLit representing a byte array literal.
// The returned literal is of the form:
// []byte{ 0x01, 0x02, 0x03, ... }.
func byteArrayCompositeLit(hex []byte) *ast.CompositeLit {
var elts []ast.Expr
// create list of byte literals
for _, b := range hex {
elts = append(elts, &ast.BasicLit{
Kind: token.INT,
Value: fmt.Sprintf("0x%02x", b),
})
}
// create the composite literal
// containing the byte literals as part of an []byte slice
return &ast.CompositeLit{
Type: &ast.ArrayType{
Elt: ast.NewIdent("byte"),
},
Elts: elts,
}
}
// measurementsEntryKeyValueExpr returns a *ast.KeyValueExpr representing a measurements.Measurement entry.
// The returned expression is of the form:
//
// 0: {
// Expected: []byte{ 0x01, 0x02, 0x03, ... },
// WarnOnly: false,
// },
func measurementsEntryKeyValueExpr(pcr uint32, measuremnt measurements.Measurement) *ast.KeyValueExpr {
key := fmt.Sprintf("%d", pcr)
var validationOptString string
if measuremnt.ValidationOpt {
validationOptString = "WarnOnly"
} else {
validationOptString = "Enforce"
}
return &ast.KeyValueExpr{
Key: &ast.BasicLit{
Kind: token.INT,
Value: key,
},
Value: &ast.CompositeLit{
Elts: []ast.Expr{
&ast.KeyValueExpr{
Key: &ast.Ident{Name: "Expected"},
Value: byteArrayCompositeLit(measuremnt.Expected),
},
&ast.KeyValueExpr{
Key: &ast.Ident{Name: "ValidationOpt"},
Value: &ast.Ident{Name: validationOptString},
},
},
},
}
}
// measurementsCompositeLiteral returns a *ast.CompositeLit representing a measurements.M literal.
// The returned literal is of the form:
//
// M{
// 0: {
// Expected: []byte{ 0x01, 0x02, 0x03, ... },
// WarnOnly: false,
// },
// 1: {
// Expected: []byte{ 0x01, 0x02, 0x03, ... },
// WarnOnly: false,
// },
// ...
// }
func measurementsCompositeLiteral(measurements measurements.M) *ast.CompositeLit {
var elts []ast.Expr
pcrs := make([]uint32, 0, len(measurements))
for pcr := range measurements {
pcrs = append(pcrs, pcr)
}
sort.Slice(pcrs, func(i, j int) bool { return pcrs[i] < pcrs[j] })
for _, pcr := range pcrs {
kvExpr := measurementsEntryKeyValueExpr(pcr, measurements[pcr])
elts = append(elts, kvExpr)
}
return &ast.CompositeLit{
Type: &ast.Ident{
Name: "M",
},
Elts: elts,
}
}
func attestationVariantFromGoIdentifier(identifier string) (variant.Variant, error) {
switch identifier {
case "Dummy":
return variant.Dummy{}, nil
case "AWSSEVSNP":
return variant.AWSSEVSNP{}, nil
case "AWSNitroTPM":
return variant.AWSNitroTPM{}, nil
case "GCPSEVES":
return variant.GCPSEVES{}, nil
case "AzureSEVSNP":
return variant.AzureSEVSNP{}, nil
case "AzureTDX":
return variant.AzureTDX{}, nil
case "AzureTrustedLaunch":
return variant.AzureTrustedLaunch{}, nil
case "QEMUVTPM":
return variant.QEMUVTPM{}, nil
case "QEMUTDX":
return variant.QEMUTDX{}, nil
}
return nil, fmt.Errorf("unknown identifier: %q", identifier)
}
func imageVersionFromFile(path string) (string, error) {
fset := token.NewFileSet()
imageFile, err := parser.ParseFile(fset, path, nil, parser.ParseComments)
if err != nil {
log.Fatal(err)
}
var defaultImage string
_ = astutil.Apply(imageFile, func(cursor *astutil.Cursor) bool {
n := cursor.Node()
// find const of the form defaultImage = "<version>"
if clause, ok := n.(*ast.ValueSpec); ok && len(clause.Names) == 1 && len(clause.Values) == 1 {
constName := clause.Names[0].Name
constValue, ok := clause.Values[0].(*ast.BasicLit)
if !ok || constValue.Kind != token.STRING {
return true
}
if constName != "defaultImage" {
return true
}
unquoted, err := strconv.Unquote(constValue.Value)
if err != nil {
log.Printf("error parsing defaultImage: %s", err)
return true
}
defaultImage = unquoted
}
return true
}, nil,
)
if defaultImage == "" {
return "", fmt.Errorf("no defaultImage found")
}
return defaultImage, nil
}
type rekorVerifier interface {
SearchByHash(context.Context, string) ([]string, error)
VerifyEntry(context.Context, string, string) error
}