Introduce gas floor

node/CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Enforce `min_tx_gas` in mempool preverify, reject TXs where `gas_limit < max(min_gas_limit, min_tx_gas)` [#3940]
+
 ## [1.4.1] - 2025-12-04
 
 ### Added
@@ -76,6 +80,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - First `dusk-node` release
 
 <!-- Issues -->
+[#3940]: https://github.com/dusk-network/rusk/issues/3940
 [#3917]: https://github.com/dusk-network/rusk/issues/3917
 [#3874]: https://github.com/dusk-network/rusk/issues/3874
 [#3871]: https://github.com/dusk-network/rusk/issues/3871

node/src/mempool.rs

@@ -349,10 +349,16 @@ impl MempoolSrv {
                 dusk_consensus::validate_blob_sidecars(tx)?;
             }
 
-            // Check global minimum gas limit
-            let min_gas_limit = vm.min_gas_limit();
-            if tx.inner.gas_limit() < min_gas_limit {
-                return Err(TxAcceptanceError::GasLimitTooLow(min_gas_limit));
+            // Check global minimum gas limit and per-tx gas floor
+            let chain_min_gas_limit = vm.min_gas_limit();
+            let min_tx_gas = vm.min_tx_gas(tip_height);
+            let required_gas_limit =
+                core::cmp::max(chain_min_gas_limit, min_tx_gas);
+
+            if tx.inner.gas_limit() < required_gas_limit {
+                return Err(TxAcceptanceError::GasLimitTooLow(
+                    required_gas_limit,
+                ));
             }
         }
 

node/src/vm.rs

@@ -98,6 +98,7 @@ pub trait VMExecution: Send + Sync + 'static {
     fn wasm64_disabled(&self, block_height: u64) -> bool;
     fn wasm32_disabled(&self, block_height: u64) -> bool;
     fn third_party_disabled(&self, block_height: u64) -> bool;
+    fn min_tx_gas(&self, height: u64) -> u64;
 }
 
 #[allow(clippy::large_enum_variant)]

rusk/CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Add TX gas floor feature, including for well-known chain ids [#3940]
+
 ## [1.4.1] - 2025-12-04
 
 ### Added
@@ -406,6 +410,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add build system that generates keys for circuits and caches them.
 
 <!-- Issues -->
+[#3940]: https://github.com/dusk-network/rusk/issues/3940
 [#3917]: https://github.com/dusk-network/rusk/issues/3917
 [#3897]: https://github.com/dusk-network/rusk/issues/3897
 [#3894]: https://github.com/dusk-network/rusk/issues/3894

rusk/src/lib/node/vm.rs

@@ -321,6 +321,19 @@ impl VMExecution for Rusk {
             .map(|activation| activation.is_active_at(block_height))
             .unwrap_or(false)
     }
+
+    fn min_tx_gas(&self, height: u64) -> u64 {
+        self.vm_config
+            .feature(FEATURE_MIN_TX_GAS)
+            .and_then(|activation| {
+                if activation.is_active_at(height) {
+                    self.vm_config.min_tx_gas
+                } else {
+                    None
+                }
+            })
+            .unwrap_or(0)
+    }
 }
 
 fn has_unique_elements<T>(iter: T) -> bool

rusk/src/lib/node/vm/config.rs

@@ -21,6 +21,7 @@ const DEFAULT_GAS_PER_BLOB: u64 = 1_000_000;
 const DEFAULT_MIN_DEPLOY_POINTS: u64 = 5_000_000;
 const DEFAULT_MIN_DEPLOYMENT_GAS_PRICE: u64 = 2_000;
 const DEFAULT_BLOCK_GAS_LIMIT: u64 = 3 * 1_000_000_000;
+const DEFAULT_MIN_TX_GAS: u64 = 5_000_000;
 
 /// Configuration for the execution of a transaction.
 #[derive(Debug, Clone, serde::Serialize)]
@@ -45,6 +46,9 @@ pub struct Config {
     #[serde(with = "humantime_serde")]
     pub generation_timeout: Option<Duration>,
 
+    /// Optional minimum gas charged for any transaction.
+    pub min_tx_gas: Option<u64>,
+
     /// Set of features to activate
     features: HashMap<String, FeatureActivation>,
 }
@@ -61,6 +65,7 @@ pub(crate) mod feature {
     pub const FEATURE_DISABLE_WASM64: &str = "DISABLE_WASM64";
     pub const FEATURE_DISABLE_WASM32: &str = "DISABLE_WASM32";
     pub const FEATURE_DISABLE_3RD_PARTY: &str = "DISABLE_3RD_PARTY";
+    pub const FEATURE_MIN_TX_GAS: &str = "MIN_TX_GAS";
 
     pub const HQ_KECCAK256: &str = "HQ_KECCAK256";
 }
@@ -73,6 +78,7 @@ impl Config {
             min_deployment_gas_price: DEFAULT_MIN_DEPLOYMENT_GAS_PRICE,
             min_deploy_points: DEFAULT_MIN_DEPLOY_POINTS,
             block_gas_limit: DEFAULT_BLOCK_GAS_LIMIT,
+            min_tx_gas: None,
             generation_timeout: None,
             features: HashMap::new(),
         }
@@ -121,6 +127,12 @@ impl Config {
         self
     }
 
+    /// Set the minimum gas charged for any transaction.
+    pub const fn with_min_tx_gas(mut self, min_tx_gas: u64) -> Self {
+        self.min_tx_gas = Some(min_tx_gas);
+        self
+    }
+
     /// Create a new `Config` with the given parameters.
     pub fn to_execution_config(&self, block_height: u64) -> ExecutionConfig {
         let with_public_sender: bool = self
@@ -143,11 +155,22 @@ impl Config {
             .feature(feature::FEATURE_DISABLE_3RD_PARTY)
             .map(|activation| activation.is_active_at(block_height))
             .unwrap_or_default();
+        let min_tx_gas = if self
+            .feature(feature::FEATURE_MIN_TX_GAS)
+            .map(|activation| activation.is_active_at(block_height))
+            .unwrap_or_default()
+        {
+            self.min_tx_gas.unwrap_or(0)
+        } else {
+            0
+        };
+
         ExecutionConfig {
             gas_per_blob: self.gas_per_blob,
             gas_per_deploy_byte: self.gas_per_deploy_byte,
             min_deploy_points: self.min_deploy_points,
             min_deploy_gas_price: self.min_deployment_gas_price,
+            min_tx_gas,
             with_public_sender,
             with_blob,
             disable_wasm64,

rusk/src/lib/node/vm/config/known.rs

@@ -10,7 +10,9 @@ use std::sync::LazyLock;
 
 use dusk_vm::FeatureActivation;
 
-use crate::node::{FEATURE_DISABLE_3RD_PARTY, FEATURE_DISABLE_WASM32};
+use crate::node::{
+    FEATURE_DISABLE_3RD_PARTY, FEATURE_DISABLE_WASM32, FEATURE_MIN_TX_GAS,
+};
 
 use super::feature::{
     FEATURE_ABI_PUBLIC_SENDER, FEATURE_BLOB, FEATURE_DISABLE_WASM64,
@@ -19,6 +21,7 @@ use super::feature::{
 use super::{
     DEFAULT_BLOCK_GAS_LIMIT, DEFAULT_GAS_PER_BLOB, DEFAULT_GAS_PER_DEPLOY_BYTE,
     DEFAULT_MIN_DEPLOYMENT_GAS_PRICE, DEFAULT_MIN_DEPLOY_POINTS,
+    DEFAULT_MIN_TX_GAS,
 };
 
 pub const MAINNET_ID: u8 = 1;
@@ -36,7 +39,8 @@ pub struct WellKnownConfig {
     pub min_deploy_points: u64,
     pub min_deployment_gas_price: u64,
     pub block_gas_limit: u64,
-    pub features: [(&'static str, FeatureActivation); 6],
+    pub min_tx_gas: Option<u64>,
+    pub features: [(&'static str, FeatureActivation); 7],
 }
 
 impl WellKnownConfig {
@@ -87,13 +91,15 @@ static MAINNET_CONFIG: LazyLock<WellKnownConfig> =
         min_deploy_points: DEFAULT_MIN_DEPLOY_POINTS,
         min_deployment_gas_price: DEFAULT_MIN_DEPLOYMENT_GAS_PRICE,
         block_gas_limit: DEFAULT_BLOCK_GAS_LIMIT,
+        min_tx_gas: None,
         features: [
             (FEATURE_ABI_PUBLIC_SENDER, MAINNET_SENDER_ACTIVATION_HEIGHT),
             (HQ_KECCAK256, NEVER),
             (FEATURE_BLOB, MAINNET_BLOB_ACTIVATION),
             (FEATURE_DISABLE_WASM64, MAINNET_DISABLE_WASM_64.clone()),
             (FEATURE_DISABLE_WASM32, MAINNET_3RD_PARTY_OFF.clone()),
             (FEATURE_DISABLE_3RD_PARTY, MAINNET_3RD_PARTY_OFF.clone()),
+            (FEATURE_MIN_TX_GAS, NEVER),
         ],
     });
 
@@ -108,13 +114,15 @@ const TESTNET_CONFIG: WellKnownConfig = WellKnownConfig {
     min_deploy_points: DEFAULT_MIN_DEPLOY_POINTS,
     min_deployment_gas_price: DEFAULT_MIN_DEPLOYMENT_GAS_PRICE,
     block_gas_limit: DEFAULT_BLOCK_GAS_LIMIT,
+    min_tx_gas: None,
     features: [
         (FEATURE_ABI_PUBLIC_SENDER, GENESIS),
         (HQ_KECCAK256, NEVER),
         (FEATURE_BLOB, TESTNET_AT_12_11_2025_AT_09_00_UTC),
         (FEATURE_DISABLE_WASM64, TESTNET_AT_12_11_2025_AT_09_00_UTC),
         (FEATURE_DISABLE_WASM32, NEVER),
         (FEATURE_DISABLE_3RD_PARTY, NEVER),
+        (FEATURE_MIN_TX_GAS, NEVER),
     ],
 };
 
@@ -125,13 +133,15 @@ const DEVNET_CONFIG: WellKnownConfig = WellKnownConfig {
     min_deploy_points: DEFAULT_MIN_DEPLOY_POINTS,
     min_deployment_gas_price: DEFAULT_MIN_DEPLOYMENT_GAS_PRICE,
     block_gas_limit: DEFAULT_BLOCK_GAS_LIMIT,
+    min_tx_gas: None,
     features: [
         (FEATURE_ABI_PUBLIC_SENDER, GENESIS),
         (HQ_KECCAK256, GENESIS),
         (FEATURE_BLOB, GENESIS),
         (FEATURE_DISABLE_WASM64, GENESIS),
         (FEATURE_DISABLE_WASM32, NEVER),
         (FEATURE_DISABLE_3RD_PARTY, NEVER),
+        (FEATURE_MIN_TX_GAS, NEVER),
     ],
 };
 
@@ -142,12 +152,14 @@ const LOCALNET_CONFIG: WellKnownConfig = WellKnownConfig {
     min_deploy_points: DEFAULT_MIN_DEPLOY_POINTS,
     min_deployment_gas_price: DEFAULT_MIN_DEPLOYMENT_GAS_PRICE,
     block_gas_limit: DEFAULT_BLOCK_GAS_LIMIT,
+    min_tx_gas: Some(DEFAULT_MIN_TX_GAS),
     features: [
         (FEATURE_ABI_PUBLIC_SENDER, GENESIS),
         (HQ_KECCAK256, GENESIS),
         (FEATURE_BLOB, GENESIS),
         (FEATURE_DISABLE_WASM64, GENESIS),
         (FEATURE_DISABLE_WASM32, NEVER),
         (FEATURE_DISABLE_3RD_PARTY, NEVER),
+        (FEATURE_MIN_TX_GAS, GENESIS),
     ],
 };

rusk/src/lib/node/vm/config/opt.rs

@@ -43,6 +43,9 @@ pub struct OptionalConfig {
     #[serde(default, with = "humantime_serde")]
     pub generation_timeout: Option<Duration>,
 
+    /// Minimum gas charged for any transaction.
+    pub min_tx_gas: Option<u64>,
+
     /// Set of features to activate
     #[serde(default)]
     features: HashMap<String, FeatureActivation>,
@@ -111,6 +114,10 @@ impl OptionalConfig {
             config.block_gas_limit,
         );
 
+        if let Some(value) = config.min_tx_gas {
+            Self::set_or_warn("min_tx_gas", &mut self.min_tx_gas, value);
+        }
+
         for (feature, activation) in &config.features {
             if let Some(v) = self.feature(feature) {
                 if v != activation {
@@ -192,6 +199,7 @@ impl TryFrom<OptionalConfig> for Config {
             block_gas_limit: value
                 .block_gas_limit
                 .ok_or(anyhow!("Missing block_gas_limit"))?,
+            min_tx_gas: value.min_tx_gas,
             generation_timeout: value.generation_timeout,
             features: value.features,
         })

rusk/tests/services/gas_behavior.rs

@@ -20,7 +20,7 @@ use tempfile::tempdir;
 use tracing::info;
 
 use crate::common::logger;
-use crate::common::state::{generator_procedure, new_state};
+use crate::common::state::{generator_procedure, new_state, ExecuteResult};
 use crate::common::wallet::{
     test_wallet as wallet, TestStateClient, TestStore,
 };
@@ -34,6 +34,8 @@ const GAS_LIMIT_0: u64 = 100_000_000;
 const GAS_LIMIT_1: u64 = 300_000_000;
 const GAS_PRICE: u64 = 1;
 const DEPOSIT: u64 = 0;
+const MIN_TX_GAS: u64 = 5_000_000;
+const LOW_GAS_LIMIT: u64 = 1_000_000;
 
 // Creates the Rusk initial state for the tests below
 async fn initial_state<P: AsRef<Path>>(dir: P) -> Result<Rusk> {
@@ -130,6 +132,13 @@ fn make_transactions(
         tx_1.gas_spent < GAS_LIMIT_1,
         "Successful transaction should consume less than provided"
     );
+    assert!(
+        tx_1.gas_spent >= MIN_TX_GAS,
+        "Successful transaction should be charged at least MIN_TX_GAS \
+         (got {}, expected >= {})",
+        tx_1.gas_spent,
+        MIN_TX_GAS,
+    );
 }
 
 #[tokio::test(flavor = "multi_thread")]
@@ -172,3 +181,56 @@ pub async fn erroring_tx_charged_full() -> Result<()> {
 
     Ok(())
 }
+
+#[tokio::test(flavor = "multi_thread")]
+pub async fn tx_below_min_tx_gas_is_discarded() -> Result<()> {
+    // Setup the logger
+    logger();
+
+    let tmp = tempdir().expect("Should be able to create temporary directory");
+    let rusk = initial_state(&tmp).await?;
+
+    let cache = Arc::new(RwLock::new(HashMap::new()));
+
+    let wallet = wallet::Wallet::new(
+        TestStore,
+        TestStateClient {
+            rusk: rusk.clone(),
+            cache,
+        },
+    );
+
+    let mut rng = StdRng::seed_from_u64(0xbeef);
+
+    // This is the same call as in make_transactions, but with a gas_limit
+    // that is below the MIN_TX_GAS
+    let contract_call = ContractCall::new(TRANSFER_CONTRACT, "root");
+    let tx_low = wallet
+        .phoenix_execute(
+            &mut rng,
+            SENDER_INDEX_0,
+            LOW_GAS_LIMIT,
+            GAS_PRICE,
+            DEPOSIT,
+            TransactionData::Call(contract_call),
+        )
+        .expect("Making the transaction should succeed");
+
+    // With the MIN_TX_GAS feature active, this tx must be discarded
+    // during block generation
+    let res = generator_procedure(
+        &rusk,
+        &[tx_low],
+        BLOCK_HEIGHT,
+        BLOCK_GAS_LIMIT,
+        vec![],
+        Some(ExecuteResult {
+            executed: 0,
+            discarded: 1,
+        }),
+    );
+
+    res.expect("generator procedure should succeed");
+
+    Ok(())
+}

vm/CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Enforce a per‑transaction minimum gas floor [#3940]
+
 ## [1.4.1] - 2025-12-04
 
 ### Added
@@ -58,6 +62,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add vm to interact with Dusk network [#3235]
 
 <!-- Issues -->
+[#3940]: https://github.com/dusk-network/rusk/issues/3940
 [#3774]: https://github.com/dusk-network/rusk/issues/3774
 [#3235]: https://github.com/dusk-network/rusk/issues/3235
 [#3341]: https://github.com/dusk-network/rusk/issues/3341