Move predicate header parsing (#824)

Author: StephenButtolph

core/evm.go

@@ -35,7 +35,6 @@ import (
 	"github.com/ava-labs/subnet-evm/core/vm"
 	"github.com/ava-labs/subnet-evm/predicate"
 	"github.com/ethereum/go-ethereum/common"
-	"github.com/ethereum/go-ethereum/log"
 	"github.com/holiman/uint256"
 )
 
@@ -51,33 +50,6 @@ type ChainContext interface {
 
 // NewEVMBlockContext creates a new context for use in the EVM.
 func NewEVMBlockContext(header *types.Header, chain ChainContext, author *common.Address) vm.BlockContext {
-	predicateBytes, ok := predicate.GetPredicateResultBytes(header.Extra)
-	if !ok {
-		return newEVMBlockContext(header, chain, author, nil)
-	}
-	// Prior to Durango, the VM enforces the extra data is smaller than or
-	// equal to this size. After Durango, the VM pre-verifies the extra
-	// data past the dynamic fee rollup window is valid.
-	predicateResults, err := predicate.ParseResults(predicateBytes)
-	if err != nil {
-		log.Error("failed to parse predicate results creating new block context", "err", err, "extra", header.Extra)
-		// As mentioned above, we pre-verify the extra data to ensure this never happens.
-		// If we hit an error, construct a new block context rather than use a potentially half initialized value
-		// as defense in depth.
-		return newEVMBlockContext(header, chain, author, nil)
-	}
-	return newEVMBlockContext(header, chain, author, predicateResults)
-}
-
-// NewEVMBlockContextWithPredicateResults creates a new context for use in the EVM with an override for the predicate results that is not present
-// in header.Extra.
-// This function is used to create a BlockContext when the header Extra data is not fully formed yet and it's more efficient to pass in predicateResults
-// directly rather than re-encode the latest results when executing each individaul transaction.
-func NewEVMBlockContextWithPredicateResults(header *types.Header, chain ChainContext, author *common.Address, predicateResults *predicate.Results) vm.BlockContext {
-	return newEVMBlockContext(header, chain, author, predicateResults)
-}
-
-func newEVMBlockContext(header *types.Header, chain ChainContext, author *common.Address, predicateResults *predicate.Results) vm.BlockContext {
 	var (
 		beneficiary common.Address
 		baseFee     *big.Int
@@ -97,20 +69,30 @@ func newEVMBlockContext(header *types.Header, chain ChainContext, author *common
 		blobBaseFee = eip4844.CalcBlobFee(*header.ExcessBlobGas)
 	}
 	return vm.BlockContext{
-		CanTransfer:      CanTransfer,
-		Transfer:         Transfer,
-		GetHash:          GetHashFn(header, chain),
-		PredicateResults: predicateResults,
-		Coinbase:         beneficiary,
-		BlockNumber:      new(big.Int).Set(header.Number),
-		Time:             header.Time,
-		Difficulty:       new(big.Int).Set(header.Difficulty),
-		BaseFee:          baseFee,
-		BlobBaseFee:      blobBaseFee,
-		GasLimit:         header.GasLimit,
+		CanTransfer: CanTransfer,
+		Transfer:    Transfer,
+		GetHash:     GetHashFn(header, chain),
+		Extra:       header.Extra,
+		Coinbase:    beneficiary,
+		BlockNumber: new(big.Int).Set(header.Number),
+		Time:        header.Time,
+		Difficulty:  new(big.Int).Set(header.Difficulty),
+		BaseFee:     baseFee,
+		BlobBaseFee: blobBaseFee,
+		GasLimit:    header.GasLimit,
 	}
 }
 
+// NewEVMBlockContextWithPredicateResults creates a new context for use in the EVM with an override for the predicate results that is not present
+// in header.Extra.
+// This function is used to create a BlockContext when the header Extra data is not fully formed yet and it's more efficient to pass in predicateResults
+// directly rather than re-encode the latest results when executing each individaul transaction.
+func NewEVMBlockContextWithPredicateResults(header *types.Header, chain ChainContext, author *common.Address, predicateResults *predicate.Results) vm.BlockContext {
+	blockContext := NewEVMBlockContext(header, chain, author)
+	blockContext.PredicateResults = predicateResults
+	return blockContext
+}
+
 // NewEVMTxContext creates a new transaction context for a single transaction.
 func NewEVMTxContext(msg *Message) vm.TxContext {
 	ctx := vm.TxContext{

core/vm/evm.go

@@ -35,6 +35,7 @@ import (
 	"github.com/ava-labs/subnet-evm/constants"
 	"github.com/ava-labs/subnet-evm/core/types"
 	"github.com/ava-labs/subnet-evm/params"
+	"github.com/ava-labs/subnet-evm/plugin/evm/header"
 	"github.com/ava-labs/subnet-evm/precompile/contract"
 	"github.com/ava-labs/subnet-evm/precompile/contracts/deployerallowlist"
 	"github.com/ava-labs/subnet-evm/precompile/modules"
@@ -43,6 +44,7 @@ import (
 	"github.com/ava-labs/subnet-evm/vmerrs"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/ethereum/go-ethereum/log"
 	"github.com/holiman/uint256"
 )
 
@@ -111,9 +113,14 @@ type BlockContext struct {
 	Transfer TransferFunc
 	// GetHash returns the hash corresponding to n
 	GetHash GetHashFunc
-	// PredicateResults are the results of predicate verification available throughout the EVM's execution.
-	// PredicateResults may be nil if it is not encoded in the block's header.
+	// PredicateResults are the results of predicate verification available
+	// throughout the EVM's execution.
+	//
+	// PredicateResults may be nil if it is not encoded in the extra field of
+	// the block's header or if the extra field has not been parsed yet.
 	PredicateResults *predicate.Results
+	// Extra is the extra field from the block header.
+	Extra []byte
 
 	// Block information
 	Coinbase    common.Address // Provides information for COINBASE
@@ -209,6 +216,32 @@ func NewEVM(blockCtx BlockContext, txCtx TxContext, statedb StateDB, chainConfig
 		chainRules:  chainConfig.Rules(blockCtx.BlockNumber, blockCtx.Time),
 	}
 	evm.interpreter = NewEVMInterpreter(evm)
+
+	// If the predicate results were set by the miner, use them.
+	if blockCtx.PredicateResults != nil {
+		return evm
+	}
+
+	// Parse the predicate results from the extra field and store them in the
+	// block context.
+	predicateBytes := header.PredicateBytesFromExtra(blockCtx.Extra)
+	if len(predicateBytes) == 0 {
+		return evm
+	}
+
+	// The VM has already verified the correctness of the results during header
+	// validation.
+	results, err := predicate.ParseResults(predicateBytes)
+	if err != nil {
+		log.Error("Unexpected error parsing predicate results",
+			"err", err,
+		)
+		return evm
+	}
+
+	// Because the BlockContext is pass-by-value, this does not cache the
+	// results for future calls to NewEVM.
+	evm.Context.PredicateResults = results
 	return evm
 }
 

plugin/evm/block.go

@@ -17,6 +17,7 @@ import (
 	"github.com/ava-labs/subnet-evm/core/rawdb"
 	"github.com/ava-labs/subnet-evm/core/types"
 	"github.com/ava-labs/subnet-evm/params"
+	"github.com/ava-labs/subnet-evm/plugin/evm/header"
 	"github.com/ava-labs/subnet-evm/precompile/precompileconfig"
 	"github.com/ava-labs/subnet-evm/predicate"
 
@@ -242,10 +243,7 @@ func (b *Block) verifyPredicates(predicateContext *precompileconfig.PredicateCon
 		return fmt.Errorf("failed to marshal predicate results: %w", err)
 	}
 	extraData := b.ethBlock.Extra()
-	headerPredicateResultsBytes, ok := predicate.GetPredicateResultBytes(extraData)
-	if !ok {
-		return fmt.Errorf("failed to find predicate results in extra data: %x", extraData)
-	}
+	headerPredicateResultsBytes := header.PredicateBytesFromExtra(extraData)
 	if !bytes.Equal(headerPredicateResultsBytes, predicateResultsBytes) {
 		return fmt.Errorf("%w (remote: %x local: %x)", errInvalidHeaderPredicateResults, headerPredicateResultsBytes, predicateResultsBytes)
 	}

plugin/evm/header/extra.go

@@ -68,3 +68,16 @@ func VerifyExtra(rules params.AvalancheRules, extra []byte) error {
 	}
 	return nil
 }
+
+// PredicateBytesFromExtra returns the predicate result bytes from the header's
+// extra data. If the extra data is not long enough, an empty slice is returned.
+func PredicateBytesFromExtra(extra []byte) []byte {
+	// Prior to Durango, the VM enforces the extra data is smaller than or equal
+	// to this size.
+	// After Durango, the VM pre-verifies the extra data past the dynamic fee
+	// rollup window is valid.
+	if len(extra) <= FeeWindowSize {
+		return nil
+	}
+	return extra[FeeWindowSize:]
+}

plugin/evm/header/extra_test.go

@@ -183,3 +183,40 @@ func TestVerifyExtra(t *testing.T) {
 		})
 	}
 }
+
+func TestPredicateBytesFromExtra(t *testing.T) {
+	tests := []struct {
+		name     string
+		extra    []byte
+		expected []byte
+	}{
+		{
+			name:     "empty_extra",
+			extra:    nil,
+			expected: nil,
+		},
+		{
+			name:     "too_short",
+			extra:    make([]byte, FeeWindowSize-1),
+			expected: nil,
+		},
+		{
+			name:     "empty_predicate",
+			extra:    make([]byte, FeeWindowSize),
+			expected: nil,
+		},
+		{
+			name: "non_empty_predicate",
+			extra: []byte{
+				FeeWindowSize: 5,
+			},
+			expected: []byte{5},
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			got := PredicateBytesFromExtra(test.extra)
+			require.Equal(t, test.expected, got)
+		})
+	}
+}

plugin/evm/vm_warp_test.go

@@ -32,6 +32,7 @@ import (
 	"github.com/ava-labs/subnet-evm/core/types"
 	"github.com/ava-labs/subnet-evm/eth/tracers"
 	"github.com/ava-labs/subnet-evm/params"
+	customheader "github.com/ava-labs/subnet-evm/plugin/evm/header"
 	"github.com/ava-labs/subnet-evm/plugin/evm/message"
 	"github.com/ava-labs/subnet-evm/precompile/contract"
 	warpcontract "github.com/ava-labs/subnet-evm/precompile/contracts/warp"
@@ -668,8 +669,7 @@ func testReceiveWarpMessage(
 
 	// Require the block was built with a successful predicate result
 	ethBlock := block2.(*chain.BlockWrapper).Block.(*Block).ethBlock
-	headerPredicateResultsBytes, ok := predicate.GetPredicateResultBytes(ethBlock.Extra())
-	require.True(ok)
+	headerPredicateResultsBytes := customheader.PredicateBytesFromExtra(ethBlock.Extra())
 	results, err := predicate.ParseResults(headerPredicateResultsBytes)
 	require.NoError(err)
 

predicate/predicate_bytes.go

@@ -6,7 +6,6 @@ package predicate
 import (
 	"fmt"
 
-	"github.com/ava-labs/subnet-evm/plugin/evm/header"
 	"github.com/ethereum/go-ethereum/common"
 )
 
@@ -50,15 +49,3 @@ func UnpackPredicate(paddedPredicate []byte) ([]byte, error) {
 
 	return trimmedPredicateBytes[:len(trimmedPredicateBytes)-1], nil
 }
-
-// GetPredicateResultBytes returns the predicate result bytes from the extra data and
-// true iff the predicate results bytes have non-zero length.
-func GetPredicateResultBytes(extraData []byte) ([]byte, bool) {
-	// Prior to Durango, the VM enforces the extra data is smaller than or equal to this size.
-	// After Durango, the VM pre-verifies the extra data past the dynamic fee rollup window is
-	// valid.
-	if len(extraData) <= header.FeeWindowSize {
-		return nil, false
-	}
-	return extraData[header.FeeWindowSize:], true
-}

predicate/predicate_bytes_test.go

@@ -8,7 +8,6 @@ import (
 	"testing"
 
 	"github.com/ava-labs/avalanchego/utils"
-	"github.com/ava-labs/subnet-evm/plugin/evm/header"
 	"github.com/stretchr/testify/require"
 )
 
@@ -49,18 +48,3 @@ func TestUnpackInvalidPredicate(t *testing.T) {
 		}
 	}
 }
-
-func TestPredicateResultsBytes(t *testing.T) {
-	require := require.New(t)
-	dataTooShort := utils.RandomBytes(header.FeeWindowSize - 1)
-	_, ok := GetPredicateResultBytes(dataTooShort)
-	require.False(ok)
-
-	preDurangoData := utils.RandomBytes(header.FeeWindowSize)
-	_, ok = GetPredicateResultBytes(preDurangoData)
-	require.False(ok)
-	postDurangoData := utils.RandomBytes(header.FeeWindowSize + 2)
-	resultBytes, ok := GetPredicateResultBytes(postDurangoData)
-	require.True(ok)
-	require.Equal(resultBytes, postDurangoData[header.FeeWindowSize:])
-}