mirror of
https://github.com/edgelesssys/constellation.git
synced 2024-10-01 01:36:09 -04:00
306 lines
9.3 KiB
Go
306 lines
9.3 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 main
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import (
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"bytes"
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"context"
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"encoding/base64"
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"fmt"
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"go/ast"
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"go/parser"
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"go/printer"
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"go/token"
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"log"
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"net/http"
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"net/url"
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"os"
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"path"
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"sort"
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"strconv"
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"strings"
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"github.com/edgelesssys/constellation/v2/internal/attestation/measurements"
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"github.com/edgelesssys/constellation/v2/internal/cloud/cloudprovider"
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"github.com/edgelesssys/constellation/v2/internal/config"
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"github.com/edgelesssys/constellation/v2/internal/constants"
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"github.com/edgelesssys/constellation/v2/internal/sigstore"
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"github.com/edgelesssys/constellation/v2/internal/versionsapi"
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"golang.org/x/tools/go/ast/astutil"
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)
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// this tool is used to generate hardcoded measurements for the enterprise build.
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// Measurements are embedded in the constellation cli.
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func main() {
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defaultConf := config.Default()
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log.Printf("Generating measurements for %s\n", defaultConf.Image)
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const filePath = "./measurements_enterprise.go"
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ctx := context.Background()
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fset := token.NewFileSet()
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file, err := parser.ParseFile(fset, filePath, nil, parser.ParseComments)
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if err != nil {
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log.Fatal(err)
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}
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rekor, err := sigstore.NewRekor()
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if err != nil {
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log.Fatal(err)
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}
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var returnStmtCtr int
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newFile := astutil.Apply(file, func(cursor *astutil.Cursor) bool {
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n := cursor.Node()
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// find all switch cases for the CSPs of the form:
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// switch provider {
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// case cloudprovider.XYZ:
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// return M{...}
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if clause, ok := n.(*ast.CaseClause); ok && len(clause.List) > 0 && len(clause.Body) > 0 {
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sel, ok := clause.List[0].(*ast.SelectorExpr)
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if !ok {
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return true
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}
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returnStmt, ok := clause.Body[0].(*ast.ReturnStmt)
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if !ok || len(returnStmt.Results) == 0 {
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return true
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}
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provider := cloudprovider.FromString(sel.Sel.Name)
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if provider == cloudprovider.Unknown {
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log.Fatalf("unknown provider %s", sel.Sel.Name)
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}
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log.Println("Found", provider)
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returnStmtCtr++
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// retrieve and validate measurements for the given CSP and image
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measuremnts := mustGetMeasurements(ctx, rekor, []byte(constants.CosignPublicKey), http.DefaultClient, provider, defaultConf.Image)
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// replace the return statement with a composite literal containing the validated measurements
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returnStmt.Results[0] = measurementsCompositeLiteral(measuremnts, returnStmt.Return+7)
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}
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return true
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}, nil,
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)
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if returnStmtCtr == 0 {
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log.Fatal("no measurements updated")
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}
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var buf bytes.Buffer
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printConfig := printer.Config{Mode: printer.UseSpaces | printer.TabIndent, Tabwidth: 8}
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if err = printConfig.Fprint(&buf, fset, newFile); err != nil {
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log.Fatalf("error formatting file %s: %s", filePath, err)
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}
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if err := os.WriteFile(filePath, buf.Bytes(), 0o644); err != nil {
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log.Fatalf("error writing file %s: %s", filePath, err)
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}
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log.Println("Successfully generated hashes.")
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}
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// mustGetMeasurements fetches the measurements for the given image and CSP and verifies them.
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func mustGetMeasurements(ctx context.Context, verifier rekorVerifier, cosignPublicKey []byte, client *http.Client, provider cloudprovider.Provider, image string) measurements.M {
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measurementsURL, err := measurementURL(provider, image, "measurements.json")
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if err != nil {
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panic(err)
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}
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signatureURL, err := measurementURL(provider, image, "measurements.json.sig")
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if err != nil {
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panic(err)
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}
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log.Println("Fetching measurements from", measurementsURL, "and signature from", signatureURL)
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var fetchedMeasurements measurements.M
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hash, err := fetchedMeasurements.FetchAndVerify(
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ctx, client,
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measurementsURL,
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signatureURL,
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cosignPublicKey,
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measurements.WithMetadata{
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CSP: provider,
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Image: image,
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},
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)
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if err != nil {
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panic(err)
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}
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if err := verifyWithRekor(ctx, verifier, hash); err != nil {
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panic(err)
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}
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return fetchedMeasurements
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}
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// measurementURL returns the URL for the measurements file for the given image and CSP.
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func measurementURL(provider cloudprovider.Provider, image, file string) (*url.URL, error) {
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version, err := versionsapi.NewVersionFromShortPath(image, versionsapi.VersionKindImage)
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if err != nil {
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return nil, fmt.Errorf("parsing image name: %w", err)
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}
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return url.Parse(
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version.ArtifactURL() + path.Join("/image", "csp", strings.ToLower(provider.String()), file),
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)
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}
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// verifyWithRekor verifies that the given hash is present in rekor and is valid.
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func verifyWithRekor(ctx context.Context, verifier rekorVerifier, hash string) error {
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uuids, err := verifier.SearchByHash(ctx, hash)
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if err != nil {
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return fmt.Errorf("searching Rekor for hash: %w", err)
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}
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if len(uuids) == 0 {
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return fmt.Errorf("no matching entries in Rekor")
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}
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// We expect the first entry in Rekor to be our original entry.
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// SHA256 should ensure there is no entry with the same hash.
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// Any subsequent hashes are treated as potential attacks and are ignored.
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// Attacks on Rekor will be monitored from other backend services.
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artifactUUID := uuids[0]
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return verifier.VerifyEntry(
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ctx, artifactUUID,
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base64.StdEncoding.EncodeToString([]byte(constants.CosignPublicKey)),
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)
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}
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// byteArrayCompositeLit returns a *ast.CompositeLit representing a byte array literal.
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// The returned literal is of the form:
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// [32]byte{ 0x01, 0x02, 0x03, ... }.
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func byteArrayCompositeLit(hex [32]byte, pos token.Pos) *ast.CompositeLit {
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var elts []ast.Expr
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// calculate the absolute byte offsets of the elements
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// given the starting position
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curPos := pos + 16 // 16 = len("[32]byte{") + padding
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// create list of byte literals
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for i, b := range hex {
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elts = append(elts, &ast.BasicLit{
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ValuePos: curPos,
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Kind: token.INT,
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Value: fmt.Sprintf("0x%02x", b),
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})
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if (i+1)%8 == 0 {
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curPos += 11 // line break
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} else {
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curPos += 6 // 6 = len("0x00, ")
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}
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}
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// create the composite literal
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// containing the byte literals as part of an [32]byte array
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return &ast.CompositeLit{
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Type: &ast.ArrayType{
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Lbrack: pos,
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Len: ast.NewIdent("32"),
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Elt: ast.NewIdent("byte"),
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},
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Lbrace: pos + 8, // 8 = len("[32]byte")
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Elts: elts,
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Rbrace: pos + 223, // 223 = len("[32]byte{0x00, 0x01, ...}") - 1
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}
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}
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// measurementsEntryKeyValueExpr returns a *ast.KeyValueExpr representing a measurements.Measurement entry.
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// The returned expression is of the form:
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//
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// 0: {
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// Expected: [32]byte{ 0x01, 0x02, 0x03, ... },
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// WarnOnly: false,
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// },
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func measurementsEntryKeyValueExpr(pcr uint32, measuremnt measurements.Measurement, pos token.Pos) (*ast.KeyValueExpr, token.Pos) {
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// calculate the absolute byte offsets of the elements
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// given the starting position
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key := fmt.Sprintf("%d", pcr)
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keyLen := len(key)
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colon := pos + token.Pos(keyLen) // len(key)
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valuePos := colon + 2 // 2 = len(": ")
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expectedKeyPos := valuePos + 5 // 5 = padding + newline
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expectedColon := expectedKeyPos + 8 // 8 = len("Expected")
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expectedValuePos := expectedColon + 2 // 2 = len(": ")
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warnOnlyKeyPos := expectedColon + 1 + byteArrayCompositeLitWidth // 1 = space
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warnOnlyColon := warnOnlyKeyPos + 9 // 9 = len("WarnOnly")
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warnOnlyValuePos := warnOnlyColon + 2 // 2 = len(": ")
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var rbrace token.Pos
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if measuremnt.WarnOnly {
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rbrace = warnOnlyValuePos + 9 // 9 = len("true") + padding
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} else {
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rbrace = warnOnlyValuePos + 10 // 10 = len("false") + padding
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}
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return &ast.KeyValueExpr{
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Key: &ast.BasicLit{
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ValuePos: pos,
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Kind: token.INT,
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Value: key,
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},
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Colon: colon,
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Value: &ast.CompositeLit{
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Lbrace: valuePos,
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Elts: []ast.Expr{
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&ast.KeyValueExpr{
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Key: &ast.Ident{NamePos: expectedKeyPos, Name: "Expected"},
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Colon: expectedColon,
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Value: byteArrayCompositeLit(measuremnt.Expected, expectedValuePos),
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},
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&ast.KeyValueExpr{
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Key: &ast.Ident{NamePos: warnOnlyKeyPos, Name: "WarnOnly"},
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Colon: warnOnlyColon,
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Value: &ast.Ident{NamePos: warnOnlyValuePos, Name: strconv.FormatBool(measuremnt.WarnOnly)},
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},
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},
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Rbrace: rbrace,
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},
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}, rbrace + 1 // 1 = len(",")
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}
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// measurementsCompositeLiteral returns a *ast.CompositeLit representing a measurements.M literal.
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// The returned literal is of the form:
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//
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// M{
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// 0: {
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// Expected: [32]byte{ 0x01, 0x02, 0x03, ... },
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// WarnOnly: false,
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// },
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// 1: {
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// Expected: [32]byte{ 0x01, 0x02, 0x03, ... },
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// WarnOnly: false,
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// },
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// ...
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// }
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func measurementsCompositeLiteral(measurements measurements.M, pos token.Pos) *ast.CompositeLit {
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lbrace := pos + 1 // 1 = len("M")
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var elts []ast.Expr
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pcrs := make([]uint32, 0, len(measurements))
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for pcr := range measurements {
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pcrs = append(pcrs, pcr)
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}
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sort.Slice(pcrs, func(i, j int) bool { return pcrs[i] < pcrs[j] })
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entryPos := lbrace + 5 // 5 = padding + newline
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for _, pcr := range pcrs {
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kvExpr, newEntryPos := measurementsEntryKeyValueExpr(pcr, measurements[pcr], entryPos)
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elts = append(elts, kvExpr)
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entryPos = newEntryPos + 4 // 4 = padding + newline
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}
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return &ast.CompositeLit{
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Lbrace: lbrace,
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Type: &ast.Ident{
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NamePos: pos,
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Name: "M",
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},
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Elts: elts,
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Rbrace: entryPos - 1, // -1 = closing brace is not indented
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}
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}
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const byteArrayCompositeLitWidth = 235
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type rekorVerifier interface {
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SearchByHash(context.Context, string) ([]string, error)
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VerifyEntry(context.Context, string, string) error
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}
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