consensus: deprecate time iota ms (#5792)

time_iota_ms is intended to ensure that an honest validator always generates timestamps 
with time increasing monotonically. For this purpose, it always suffices to have this parameter
set to `1ms`. Allowing users to choose different numbers increases bug surface area.
Thus the code now ignores the user provided time_iota_ms parameter (marking it as unused), 
and uses 1ms internally.

CHANGELOG_PENDING.md

@@ -43,6 +43,7 @@ Friendly reminder, we have a [bug bounty program](https://hackerone.com/tendermi
 - [blockchain/v0] \#5741 Relax termination conditions and increase sync timeout (@melekes)
 - [cli] \#5772 `gen_node_key` output now contains node ID (`id` field) (@melekes)
 - [blockchain/v2] \#5774 Send status request when new peer joins (@melekes)
+- [consensus] \#5792 Deprecates the `time_iota_ms` consensus parameter, to reduce the bug surface. The parameter is no longer used. (@valardragon)
 
 ### BUG FIXES
 

config/config.go

@@ -825,7 +825,6 @@ type ConsensusConfig struct {
 	// How long we wait after committing a block, before starting on the new
 	// height (this gives us a chance to receive some more precommits, even
 	// though we already have +2/3).
-	// NOTE: when modifying, make sure to update time-iota-ms genesis parameter
 	TimeoutCommit time.Duration `mapstructure:"timeout-commit"`
 
 	// Make progress as soon as we have all the precommits (as if TimeoutCommit = 0)
@@ -871,7 +870,6 @@ func TestConsensusConfig() *ConsensusConfig {
 	cfg.TimeoutPrevoteDelta = 1 * time.Millisecond
 	cfg.TimeoutPrecommit = 10 * time.Millisecond
 	cfg.TimeoutPrecommitDelta = 1 * time.Millisecond
-	// NOTE: when modifying, make sure to update time_iota_ms (testGenesisFmt) in toml.go
 	cfg.TimeoutCommit = 10 * time.Millisecond
 	cfg.SkipTimeoutCommit = true
 	cfg.PeerGossipSleepDuration = 5 * time.Millisecond

consensus/state.go

@@ -2098,12 +2098,17 @@ func (cs *State) signVote(
 	return vote, err
 }
 
+// voteTime ensures monotonicity of the time a validator votes on.
+// It ensures that for a prior block with a BFT-timestamp of T,
+// any vote from this validator will have time at least time T + 1ms.
+// This is needed, as monotonicity of time is a guarantee that BFT time provides.
 func (cs *State) voteTime() time.Time {
 	now := tmtime.Now()
 	minVoteTime := now
+	// Minimum time increment between blocks
+	const timeIota = time.Millisecond
 	// TODO: We should remove next line in case we don't vote for v in case cs.ProposalBlock == nil,
 	// even if cs.LockedBlock != nil. See https://docs.tendermint.com/master/spec/.
-	timeIota := time.Duration(cs.state.ConsensusParams.Block.TimeIotaMs) * time.Millisecond
 	if cs.LockedBlock != nil {
 		// See the BFT time spec https://docs.tendermint.com/master/spec/consensus/bft-time.html
 		minVoteTime = cs.LockedBlock.Time.Add(timeIota)

docs/tendermint-core/using-tendermint.md

@@ -53,9 +53,7 @@ definition](https://github.com/tendermint/tendermint/blob/master/types/genesis.g
     - `block`
         - `max_bytes`: Max block size, in bytes.
         - `max_gas`: Max gas per block.
-        - `time_iota_ms`: Minimum time increment between consecutive blocks (in
-      milliseconds). If the block header timestamp is ahead of the system clock,
-      decrease this value.
+        - `time_iota_ms`: Unused. This has been deprecated and will be removed in a future version.
     - `evidence`
         - `max_age_num_blocks`: Max age of evidence, in blocks. The basic formula
       for calculating this is: MaxAgeDuration / {average block time}.

proto/tendermint/types/params.proto

@@ -25,10 +25,7 @@ message BlockParams {
   // Max gas per block.
   // Note: must be greater or equal to -1
   int64 max_gas = 2;
-  // Minimum time increment between consecutive blocks (in milliseconds) If the
-  // block header timestamp is ahead of the system clock, decrease this value.
-  //
-  // Not exposed to the application.
+  // This parameter is unused.
   int64 time_iota_ms = 3;
 }
 

types/params.go

@@ -36,7 +36,7 @@ func DefaultBlockParams() tmproto.BlockParams {
 	return tmproto.BlockParams{
 		MaxBytes:   22020096, // 21MB
 		MaxGas:     -1,
-		TimeIotaMs: 1000, // 1s
+		TimeIotaMs: 1, // 1s, parameter is now unused
 	}
 }