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AB#2316 Configurable enforced PCRs (#361)

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* Add warnings for non enforced, untrusted PCRs

* Fix global state in Config PCR map

Signed-off-by: Daniel Weiße <dw@edgeless.systems>
This commit is contained in:
Daniel Weiße 2022-08-12 15:59:45 +02:00 • committed by GitHub
parent 9478303f80
commit ba4471a228
30 changed files with 350 additions and 323 deletions
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37
internal/attestation/vtpm/attestation.go
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@ -51,6 +51,11 @@ type (
VerifyUserData func(pub crypto.PublicKey, hash crypto.Hash, hashed, sig []byte) error
)
// WarnLogger is a logger used to print warnings during attestation validation.
type WarnLogger interface {
Warnf(format string, args ...interface{})
}
// AttestationDocument contains the TPM attestation with signed user data.
type AttestationDocument struct {
// Attestation contains the TPM event log, PCR values and quotes, and public key of the key used to sign the attestation.
@ -122,22 +127,39 @@ func (i *Issuer) Issue(userData []byte, nonce []byte) ([]byte, error) {
// Validator handles validation of TPM based attestation.
type Validator struct {
trustedPcrs map[uint32][]byte
expectedPCRs map[uint32][]byte
enforcedPCRs map[uint32]struct{}
getTrustedKey GetTPMTrustedAttestationPublicKey
validateCVM ValidateCVM
verifyUserData VerifyUserData
log WarnLogger
}
// NewValidator returns a new Validator.
func NewValidator(trustedPcrs map[uint32][]byte, getTrustedKey GetTPMTrustedAttestationPublicKey, validateCVM ValidateCVM, verifyUserData VerifyUserData) *Validator {
func NewValidator(expectedPCRs map[uint32][]byte, enforcedPCRs []uint32,
getTrustedKey GetTPMTrustedAttestationPublicKey, validateCVM ValidateCVM, verifyUserData VerifyUserData,
) *Validator {
// Convert the enforced PCR list to a map for convenient and fast lookup
enforcedMap := make(map[uint32]struct{})
for _, pcr := range enforcedPCRs {
enforcedMap[pcr] = struct{}{}
}
return &Validator{
trustedPcrs: trustedPcrs,
expectedPCRs: expectedPCRs,
enforcedPCRs: enforcedMap,
getTrustedKey: getTrustedKey,
validateCVM: validateCVM,
verifyUserData: verifyUserData,
}
}
// AddLogger adds a logger to the validator.
func (v *Validator) AddLogger(log WarnLogger) {
v.log = log
}
// Validate a TPM based attestation.
func (v *Validator) Validate(attDocRaw []byte, nonce []byte) ([]byte, error) {
var attDoc AttestationDocument
@ -173,9 +195,14 @@ func (v *Validator) Validate(attDocRaw []byte, nonce []byte) ([]byte, error) {
if err != nil {
return nil, err
}
for idx, pcr := range v.trustedPcrs {
for idx, pcr := range v.expectedPCRs {
if !bytes.Equal(pcr, attDoc.Attestation.Quotes[quoteIdx].Pcrs.Pcrs[idx]) {
return nil, fmt.Errorf("untrusted PCR value at PCR index %d", idx)
if _, ok := v.enforcedPCRs[idx]; ok {
return nil, fmt.Errorf("untrusted PCR value at PCR index %d", idx)
}
if v.log != nil {
v.log.Warnf("Encountered untrusted PCR value at index %d", idx)
}
}
}