Merge branch 'unstable' of https://github.com/sigp/lighthouse into gloas-block-and-bid-production

consensus/types/src/state/beacon_state.rs

@@ -55,9 +55,21 @@ use crate::{
 };
 
 pub const CACHED_EPOCHS: usize = 3;
+
+// Pre-electra WS calculations are not supported. On mainnet, pre-electra epochs are outside the weak subjectivity
+// period. The default pre-electra WS value is set to 256 to allow for `basic-sim``, `fallback-sim`` test case `revert_minority_fork_on_resume`
+// to pass. 256 is a small enough number to trigger the WS safety check pre-electra on mainnet.
+pub const DEFAULT_PRE_ELECTRA_WS_PERIOD: u64 = 256;
+
 const MAX_RANDOM_BYTE: u64 = (1 << 8) - 1;
 const MAX_RANDOM_VALUE: u64 = (1 << 16) - 1;
 
+// `SAFETY_DECAY` is defined as the maximum percentage tolerable loss in the one-third
+// safety margin of FFG finality. Thus, any attack exploiting the Weak Subjectivity Period has
+// a safety margin of at least `1/3 - SAFETY_DECAY/100`.
+// Spec: https://github.com/ethereum/consensus-specs/blob/1937aff86b41b5171a9bc3972515986f1bbbf303/specs/phase0/weak-subjectivity.md?plain=1#L50-L71
+const SAFETY_DECAY: u64 = 10;
+
 pub type Validators<E> = List<Validator, <E as EthSpec>::ValidatorRegistryLimit>;
 pub type Balances<E> = List<u64, <E as EthSpec>::ValidatorRegistryLimit>;
 
@@ -3007,6 +3019,26 @@ impl<E: EthSpec> BeaconState<E> {
         Ok(())
     }
 
+    /// Returns the weak subjectivity period for `self`
+    pub fn compute_weak_subjectivity_period(
+        &self,
+        spec: &ChainSpec,
+    ) -> Result<Epoch, BeaconStateError> {
+        let total_active_balance = self.get_total_active_balance()?;
+        let fork_name = self.fork_name_unchecked();
+
+        if fork_name.electra_enabled() {
+            let balance_churn_limit = self.get_balance_churn_limit(spec)?;
+            compute_weak_subjectivity_period_electra(
+                total_active_balance,
+                balance_churn_limit,
+                spec,
+            )
+        } else {
+            Ok(Epoch::new(DEFAULT_PRE_ELECTRA_WS_PERIOD))
+        }
+    }
+
     /// Get the payload timeliness committee for the given `slot`.
     ///
     /// Requires the committee cache to be initialized.
@@ -3382,3 +3414,75 @@ impl<'de, E: EthSpec> ContextDeserialize<'de, ForkName> for BeaconState<E> {
         ))
     }
 }
+
+/// Spec: https://github.com/ethereum/consensus-specs/blob/1937aff86b41b5171a9bc3972515986f1bbbf303/specs/electra/weak-subjectivity.md?plain=1#L30
+pub fn compute_weak_subjectivity_period_electra(
+    total_active_balance: u64,
+    balance_churn_limit: u64,
+    spec: &ChainSpec,
+) -> Result<Epoch, BeaconStateError> {
+    let epochs_for_validator_set_churn = SAFETY_DECAY
+        .safe_mul(total_active_balance)?
+        .safe_div(balance_churn_limit.safe_mul(200)?)?;
+    let ws_period = spec
+        .min_validator_withdrawability_delay
+        .safe_add(epochs_for_validator_set_churn)?;
+
+    Ok(ws_period)
+}
+
+#[cfg(test)]
+mod weak_subjectivity_tests {
+    use crate::state::beacon_state::compute_weak_subjectivity_period_electra;
+    use crate::{ChainSpec, Epoch, EthSpec, MainnetEthSpec};
+
+    const GWEI_PER_ETH: u64 = 1_000_000_000;
+
+    #[test]
+    fn test_compute_weak_subjectivity_period_electra() {
+        let mut spec = MainnetEthSpec::default_spec();
+        spec.altair_fork_epoch = Some(Epoch::new(0));
+        spec.bellatrix_fork_epoch = Some(Epoch::new(0));
+        spec.capella_fork_epoch = Some(Epoch::new(0));
+        spec.deneb_fork_epoch = Some(Epoch::new(0));
+        spec.electra_fork_epoch = Some(Epoch::new(0));
+
+        // A table of some expected values:
+        // https://github.com/ethereum/consensus-specs/blob/1937aff86b41b5171a9bc3972515986f1bbbf303/specs/electra/weak-subjectivity.md?plain=1#L44-L54
+        // (total_active_balance, expected_ws_period)
+        let expected_values: Vec<(u64, u64)> = vec![
+            (1_048_576 * GWEI_PER_ETH, 665),
+            (2_097_152 * GWEI_PER_ETH, 1_075),
+            (4_194_304 * GWEI_PER_ETH, 1_894),
+            (8_388_608 * GWEI_PER_ETH, 3_532),
+            (16_777_216 * GWEI_PER_ETH, 3_532),
+            (33_554_432 * GWEI_PER_ETH, 3_532),
+            // This value cross referenced w/
+            // beacon_chain/tests/tests.rs:test_compute_weak_subjectivity_period
+            (1536 * GWEI_PER_ETH, 256),
+        ];
+
+        for (total_active_balance, expected_ws_period) in expected_values {
+            let balance_churn_limit = get_balance_churn_limit(total_active_balance, &spec);
+
+            let calculated_ws_period = compute_weak_subjectivity_period_electra(
+                total_active_balance,
+                balance_churn_limit,
+                &spec,
+            )
+            .unwrap();
+
+            assert_eq!(calculated_ws_period, expected_ws_period);
+        }
+    }
+
+    // caclulate the balance_churn_limit without dealing with states
+    // and without initializing the active balance cache
+    fn get_balance_churn_limit(total_active_balance: u64, spec: &ChainSpec) -> u64 {
+        let churn = std::cmp::max(
+            spec.min_per_epoch_churn_limit_electra,
+            total_active_balance / spec.churn_limit_quotient,
+        );
+        churn - (churn % spec.effective_balance_increment)
+    }
+}

consensus/types/src/state/mod.rs

@@ -17,7 +17,7 @@ pub use balance::Balance;
 pub use beacon_state::{
     BeaconState, BeaconStateAltair, BeaconStateBase, BeaconStateBellatrix, BeaconStateCapella,
     BeaconStateDeneb, BeaconStateElectra, BeaconStateError, BeaconStateFulu, BeaconStateGloas,
-    BeaconStateHash, BeaconStateRef, CACHED_EPOCHS,
+    BeaconStateHash, BeaconStateRef, CACHED_EPOCHS, DEFAULT_PRE_ELECTRA_WS_PERIOD,
 };
 pub use committee_cache::{
     CommitteeCache, compute_committee_index_in_epoch, compute_committee_range_in_epoch,