constellation/internal/attestation/idkeydigest/idkeydigest.go

/*
Copyright (c) Edgeless Systems GmbH

SPDX-License-Identifier: AGPL-3.0-only
*/

// Package idkeydigest provides type definitions for the `idkeydigest` value of SEV-SNP attestation.
package idkeydigest

import (
	"bytes"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"strings"
)

//go:generate stringer -type=Enforcement

// Enforcement defines the behavior of the validator when the ID key digest is not found in the expected list.
type Enforcement uint32

const (
	// Unknown is reserved for invalid configurations.
	Unknown Enforcement = iota
	// Equal will error if the reported signing key digest does not match any of the values in 'acceptedKeyDigests'.
	Equal
	// MAAFallback uses 'equal' checking for validation, but fallback to using Microsoft Azure Attestation (MAA)
	// for validation if the reported digest does not match any of the values in 'acceptedKeyDigests'.
	MAAFallback
	// WarnOnly is the same as 'equal', but only prints a warning instead of returning an error if no match is found.
	WarnOnly
)

// UnmarshalJSON implements the json.Unmarshaler interface.
func (e *Enforcement) UnmarshalJSON(b []byte) error {
	return e.unmarshal(func(val any) error {
		return json.Unmarshal(b, val)
	})
}

// MarshalJSON implements the json.Marshaler interface.
func (e Enforcement) MarshalJSON() ([]byte, error) {
	return json.Marshal(e.String())
}

// UnmarshalYAML implements the yaml.Unmarshaler interface.
func (e *Enforcement) UnmarshalYAML(unmarshal func(any) error) error {
	return e.unmarshal(unmarshal)
}

// MarshalYAML implements the yaml.Marshaler interface.
func (e Enforcement) MarshalYAML() (any, error) {
	return e.String(), nil
}

func (e *Enforcement) unmarshal(unmarshalFunc func(any) error) error {
	// Check for legacy format: EnforceIDKeyDigest might be a boolean.
	// If set to true, the value will be set to StrictChecking.
	// If set to false, the value will be set to WarnOnly.
	var legacyEnforce bool
	legacyErr := unmarshalFunc(&legacyEnforce)
	if legacyErr == nil {
		if legacyEnforce {
			*e = Equal
		} else {
			*e = WarnOnly
		}
		return nil
	}

	var enforce string
	if err := unmarshalFunc(&enforce); err != nil {
		return errors.Join(
			err,
			fmt.Errorf("trying legacy format: %w", legacyErr),
		)
	}

	*e = EnforcePolicyFromString(enforce)
	if *e == Unknown {
		return fmt.Errorf("unknown Enforcement value: %q", enforce)
	}

	return nil
}

// EnforcePolicyFromString returns Enforcement from string.
func EnforcePolicyFromString(s string) Enforcement {
	s = strings.ToLower(s)
	switch s {
	case "equal":
		return Equal
	case "maafallback":
		return MAAFallback
	case "warnonly":
		return WarnOnly
	default:
		return Unknown
	}
}

// List is a list of trusted digest values for the ID key.
type List [][]byte

type encodedList []string

// encodedDigestLength is the length of a digest in hex encoding.
const encodedDigestLength = 2 * 48

// NewList creates a new IDKeyDigests from a list of digests.
func NewList(digests [][]byte) List {
	idKeyDigests := make(List, len(digests))
	copy(idKeyDigests, digests)
	return idKeyDigests
}

// DefaultList returns the default list of accepted ID key digests.
func DefaultList() List {
	return List{
		{0x03, 0x56, 0x21, 0x58, 0x82, 0xa8, 0x25, 0x27, 0x9a, 0x85, 0xb3, 0x00, 0xb0, 0xb7, 0x42, 0x93, 0x1d, 0x11, 0x3b, 0xf7, 0xe3, 0x2d, 0xde, 0x2e, 0x50, 0xff, 0xde, 0x7e, 0xc7, 0x43, 0xca, 0x49, 0x1e, 0xcd, 0xd7, 0xf3, 0x36, 0xdc, 0x28, 0xa6, 0xe0, 0xb2, 0xbb, 0x57, 0xaf, 0x7a, 0x44, 0xa3},
	}
}

// EqualTo returns true if the List of digests is equal to the other List.
func (d List) EqualTo(other List) bool {
	if len(d) != len(other) {
		return false
	}
	for i := range d {
		if !bytes.Equal(d[i], other[i]) {
			return false
		}
	}
	return true
}

// MarshalYAML implements the yaml.Marshaler interface.
func (d List) MarshalYAML() (any, error) {
	encodedIDKeyDigests := []string{}
	for _, digest := range d {
		encodedIDKeyDigests = append(encodedIDKeyDigests, hex.EncodeToString(digest))
	}
	return encodedIDKeyDigests, nil
}

// UnmarshalYAML implements the yaml.Unmarshaler interface.
func (d *List) UnmarshalYAML(unmarshal func(any) error) error {
	var encodedDigests encodedList
	if err := unmarshal(&encodedDigests); err != nil {
		// Unmarshalling failed, IDKeyDigests might be a simple string instead of IDKeyDigests struct.
		var unmarshalledString string
		if legacyErr := unmarshal(&unmarshalledString); legacyErr != nil {
			return errors.Join(
				err,
				fmt.Errorf("trying legacy format: %w", legacyErr),
			)
		}
		encodedDigests = append(encodedDigests, unmarshalledString)
	}
	if err := d.unmarshal(encodedDigests); err != nil {
		return fmt.Errorf("unmarshalling yaml: %w", err)
	}
	return nil
}

// MarshalJSON implements the json.Marshaler interface.
func (d List) MarshalJSON() ([]byte, error) {
	encodedIDKeyDigests := []string{}
	for _, digest := range d {
		encodedIDKeyDigests = append(encodedIDKeyDigests, hex.EncodeToString(digest))
	}
	return json.Marshal(encodedIDKeyDigests)
}

// UnmarshalJSON implements the json.Unmarshaler interface.
func (d *List) UnmarshalJSON(b []byte) error {
	var encodedDigests encodedList
	if err := json.Unmarshal(b, &encodedDigests); err != nil {
		// Unmarshalling failed, IDKeyDigests might be a simple string instead of IDKeyDigests struct.
		var unmarshalledString string
		if legacyErr := json.Unmarshal(b, &unmarshalledString); legacyErr != nil {
			return errors.Join(
				err,
				fmt.Errorf("trying legacy format: %w", legacyErr),
			)
		}
		encodedDigests = []string{unmarshalledString}
	}
	if err := d.unmarshal(encodedDigests); err != nil {
		return fmt.Errorf("unmarshalling json: %w", err)
	}
	return nil
}

// unmarshal is a helper function for unmarshalling encodedIDKeyDigests into IDKeyDigests.
func (d *List) unmarshal(encodedDigests encodedList) error {
	for _, encodedDigest := range encodedDigests {
		if len(encodedDigest) != encodedDigestLength {
			return fmt.Errorf("invalid digest length: %d", len(encodedDigest))
		}
		digest, err := hex.DecodeString(encodedDigest)
		if err != nil {
			return fmt.Errorf("decoding digest: %w", err)
		}
		*d = append(*d, digest)
	}
	return nil
}