From 5ff12a5d2dcee12ecf7d12faa2a1fc4c8304bbe4 Mon Sep 17 00:00:00 2001
From: Jakub Sztandera <kubuxu@protocol.ai>
Date: Sat, 1 Aug 2020 22:01:23 +0200
Subject: [PATCH] Burn remainder of GasLimit over 1.3*gasUsed

GasToBurn = max(0, GasLimit - GasUsed + (3*GasUsed)/10)

Signed-off-by: Jakub Sztandera <kubuxu@protocol.ai>
---
 chain/vm/vm.go | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/chain/vm/vm.go b/chain/vm/vm.go
index e1e165b08..2ebd42f2a 100644
--- a/chain/vm/vm.go
+++ b/chain/vm/vm.go
@@ -37,6 +37,11 @@ var log = logging.Logger("vm")
 var actorLog = logging.Logger("actors")
 var gasOnActorExec = newGasCharge("OnActorExec", 0, 0)
 
+const (
+	gasOveruseNum   = 3
+	gasOveruseDenom = 10
+)
+
 // ResolveToKeyAddr returns the public key type of address (`BLS`/`SECP256K1`) of an account actor identified by `addr`.
 func ResolveToKeyAddr(state types.StateTree, cst cbor.IpldStore, addr address.Address) (address.Address, aerrors.ActorError) {
 	if addr.Protocol() == address.BLS || addr.Protocol() == address.SECP256K1 {
@@ -454,12 +459,27 @@ func (vm *VM) ApplyMessage(ctx context.Context, cmsg types.ChainMsg) (*ApplyRet,
 	if gasUsed < 0 {
 		gasUsed = 0
 	}
+
+	allowedGasOverUsed := gasUsed + (gasUsed*gasOveruseNum)/gasOveruseDenom
+	gasToBurn := msg.GasLimit - allowedGasOverUsed
+	if gasToBurn < 0 {
+		gasToBurn = 0
+	}
+
 	// refund unused gas
-	refund := types.BigMul(types.NewInt(uint64(msg.GasLimit-gasUsed)), msg.GasPrice)
+	refund := types.BigMul(types.NewInt(uint64(msg.GasLimit-gasUsed-gasToBurn)), msg.GasPrice)
 	if err := vm.transferFromGasHolder(msg.From, gasHolder, refund); err != nil {
 		return nil, xerrors.Errorf("failed to refund gas")
 	}
 
+	if gasToBurn > 0 {
+		// burn overallocated gas
+		burn := types.BigMul(types.NewInt(uint64(gasToBurn)), msg.GasPrice)
+		if err := vm.transferFromGasHolder(builtin.BurntFundsActorAddr, gasHolder, burn); err != nil {
+			return nil, xerrors.Errorf("failed to refund gas")
+		}
+	}
+
 	gasReward := types.BigMul(msg.GasPrice, types.NewInt(uint64(gasUsed)))
 	if err := vm.transferFromGasHolder(builtin.RewardActorAddr, gasHolder, gasReward); err != nil {
 		return nil, xerrors.Errorf("failed to give miner gas reward: %w", err)