fix: only enable circuit for BASEFEE opcode (without opcode mapping) (#1033)

* Enable `BlockCtxU256Gadget` for `BASEFEE` opcode in `scroll` feature.

* Fix to restrict `DIFFICULTY` execution state only for scroll (to avoid soundness).

Author: silathdiir

zkevm-circuits/src/evm_circuit.rs

@@ -283,11 +283,7 @@ impl<F: Field> EvmCircuit<F> {
     }
 }
 
-// the diff is from the num of valid opcodes: self-destruct?
-#[cfg(not(feature = "scroll"))]
 const FIXED_TABLE_ROWS_NO_BITWISE: usize = 3647;
-#[cfg(feature = "scroll")]
-const FIXED_TABLE_ROWS_NO_BITWISE: usize = 3646;
 const FIXED_TABLE_ROWS: usize = FIXED_TABLE_ROWS_NO_BITWISE + 3 * 65536;
 
 impl<F: Field> SubCircuit<F> for EvmCircuit<F> {

zkevm-circuits/src/evm_circuit/execution.rs

@@ -146,6 +146,8 @@ use address::AddressGadget;
 use balance::BalanceGadget;
 use begin_tx::BeginTxGadget;
 use bitwise::BitwiseGadget;
+#[cfg(feature = "scroll")]
+use block_ctx::DifficultyGadget;
 use block_ctx::{BlockCtxU160Gadget, BlockCtxU256Gadget, BlockCtxU64Gadget};
 use blockhash::BlockHashGadget;
 use byte::ByteGadget;
@@ -328,6 +330,8 @@ pub(crate) struct ExecutionConfig<F> {
     block_ctx_u64_gadget: Box<BlockCtxU64Gadget<F>>,
     block_ctx_u160_gadget: Box<BlockCtxU160Gadget<F>>,
     block_ctx_u256_gadget: Box<BlockCtxU256Gadget<F>>,
+    #[cfg(feature = "scroll")]
+    difficulty_gadget: Box<DifficultyGadget<F>>,
     // error gadgets
     error_oog_call: Box<ErrorOOGCallGadget<F>>,
     error_oog_precompile: Box<ErrorOOGPrecompileGadget<F>>,
@@ -606,6 +610,8 @@ impl<F: Field> ExecutionConfig<F> {
             block_ctx_u64_gadget: configure_gadget!(),
             block_ctx_u160_gadget: configure_gadget!(),
             block_ctx_u256_gadget: configure_gadget!(),
+            #[cfg(feature = "scroll")]
+            difficulty_gadget: configure_gadget!(),
             // error gadgets
             error_oog_constant: configure_gadget!(),
             error_oog_static_memory_gadget: configure_gadget!(),
@@ -1439,6 +1445,8 @@ impl<F: Field> ExecutionConfig<F> {
             ExecutionState::BLOCKCTXU64 => assign_exec_step!(self.block_ctx_u64_gadget),
             ExecutionState::BLOCKCTXU160 => assign_exec_step!(self.block_ctx_u160_gadget),
             ExecutionState::BLOCKCTXU256 => assign_exec_step!(self.block_ctx_u256_gadget),
+            #[cfg(feature = "scroll")]
+            ExecutionState::DIFFICULTY => assign_exec_step!(self.difficulty_gadget),
             ExecutionState::BLOCKHASH => assign_exec_step!(self.blockhash_gadget),
             ExecutionState::SELFBALANCE => assign_exec_step!(self.selfbalance_gadget),
             ExecutionState::CREATE => assign_exec_step!(self.create_gadget),

zkevm-circuits/src/evm_circuit/execution/block_ctx.rs

@@ -147,13 +147,16 @@ impl<F: Field> ExecutionGadget<F> for BlockCtxU160Gadget<F> {
     }
 }
 
-#[cfg(not(feature = "scroll"))]
+// TODO:
+// This gadget is used for `BASEFEE` opcode. With current `scroll` feature, it's
+// disabled by l2geth and converted to an invalid opcode.
+// <https://github.com/scroll-tech/zkevm-circuits/blob/develop/eth-types/src/evm_types/opcode_ids.rs#L1062>
+// So need to test it after `BASEFEE` opcode is enabled in scroll l2geth.
 #[derive(Clone, Debug)]
 pub(crate) struct BlockCtxU256Gadget<F> {
     value_u256: BlockCtxGadget<F, N_BYTES_WORD>,
 }
 
-#[cfg(not(feature = "scroll"))]
 impl<F: Field> ExecutionGadget<F> for BlockCtxU256Gadget<F> {
     const NAME: &'static str = "BLOCKCTXU256";
 
@@ -174,6 +177,11 @@ impl<F: Field> ExecutionGadget<F> for BlockCtxU256Gadget<F> {
         _: &Call,
         step: &ExecStep,
     ) -> Result<(), Error> {
+        if cfg!(feature = "scroll") {
+            panic!("BASEFEE is disabled by scroll for now");
+        }
+        log::debug!("BlockCtxU256Gadget assign for {:?}", step.opcode);
+
         self.value_u256
             .same_context
             .assign_exec_step(region, offset, step)?;
@@ -188,17 +196,20 @@ impl<F: Field> ExecutionGadget<F> for BlockCtxU256Gadget<F> {
     }
 }
 
+#[cfg(feature = "scroll")]
 #[derive(Clone, Debug)]
-pub(crate) struct DifficulityGadget<F> {
+pub(crate) struct DifficultyGadget<F> {
     same_context: SameContextGadget<F>,
 }
 
-impl<F: Field> ExecutionGadget<F> for DifficulityGadget<F> {
-    const NAME: &'static str = "DIFFICULITY";
+#[cfg(feature = "scroll")]
+impl<F: Field> ExecutionGadget<F> for DifficultyGadget<F> {
+    const NAME: &'static str = "DIFFICULTY";
 
-    const EXECUTION_STATE: ExecutionState = ExecutionState::BLOCKCTXU256;
+    const EXECUTION_STATE: ExecutionState = ExecutionState::DIFFICULTY;
 
     fn configure(cb: &mut EVMConstraintBuilder<F>) -> Self {
+        // Always returns 0 for scroll.
         cb.stack_push(0.expr());
         let opcode = cb.query_cell();
         // State transition
@@ -223,17 +234,10 @@ impl<F: Field> ExecutionGadget<F> for DifficulityGadget<F> {
         _: &Call,
         step: &ExecStep,
     ) -> Result<(), Error> {
-        self.same_context.assign_exec_step(region, offset, step)?;
-
-        Ok(())
+        self.same_context.assign_exec_step(region, offset, step)
     }
 }
 
-// notice in scroll ,the BASEFEE is invalid and difficulity has been
-// changed
-#[cfg(feature = "scroll")]
-pub(crate) use DifficulityGadget as BlockCtxU256Gadget;
-
 #[cfg(test)]
 mod test {
     use crate::test_util::CircuitTestBuilder;

zkevm-circuits/src/evm_circuit/step.rs

@@ -80,7 +80,9 @@ pub enum ExecutionState {
     BLOCKHASH,
     BLOCKCTXU64,  // TIMESTAMP, NUMBER, GASLIMIT
     BLOCKCTXU160, // COINBASE
-    BLOCKCTXU256, // DIFFICULTY, BASEFEE
+    BLOCKCTXU256, // BASEFEE, DIFFICULTY (for non-scroll)
+    #[cfg(feature = "scroll")]
+    DIFFICULTY, // DIFFICULTY
     CHAINID,
     SELFBALANCE,
     POP,
@@ -270,11 +272,13 @@ impl ExecutionState {
             Self::BLOCKCTXU160 => vec![OpcodeId::COINBASE],
             Self::BLOCKCTXU256 => {
                 if cfg!(feature = "scroll") {
-                    vec![OpcodeId::DIFFICULTY]
+                    vec![OpcodeId::BASEFEE]
                 } else {
                     vec![OpcodeId::DIFFICULTY, OpcodeId::BASEFEE]
                 }
             }
+            #[cfg(feature = "scroll")]
+            Self::DIFFICULTY => vec![OpcodeId::DIFFICULTY],
             Self::CHAINID => vec![OpcodeId::CHAINID],
             Self::SELFBALANCE => vec![OpcodeId::SELFBALANCE],
             Self::POP => vec![OpcodeId::POP],

zkevm-circuits/src/witness/step.rs

@@ -187,7 +187,11 @@ impl From<&circuit_input_builder::ExecStep> for ExecutionState {
                         ExecutionState::BLOCKCTXU64
                     }
                     OpcodeId::COINBASE => ExecutionState::BLOCKCTXU160,
-                    OpcodeId::DIFFICULTY | OpcodeId::BASEFEE => ExecutionState::BLOCKCTXU256,
+                    OpcodeId::BASEFEE => ExecutionState::BLOCKCTXU256,
+                    #[cfg(not(feature = "scroll"))]
+                    OpcodeId::DIFFICULTY => ExecutionState::BLOCKCTXU256,
+                    #[cfg(feature = "scroll")]
+                    OpcodeId::DIFFICULTY => ExecutionState::DIFFICULTY,
                     OpcodeId::GAS => ExecutionState::GAS,
                     OpcodeId::SAR => ExecutionState::SAR,
                     OpcodeId::SELFBALANCE => ExecutionState::SELFBALANCE,