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Implement prevrandao block_randomness in pallet-evm #246

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Implement prevrandao block_randomness in pallet-evm #246

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14fa752
add randomness provider to pallet-evm
snowmead Apr 17, 2025
98abedf
remove unused const
snowmead Apr 17, 2025
fc9ed63
add warning for insecure randomness
snowmead Apr 17, 2025
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15 changes: 14 additions & 1 deletion frame/ethereum/src/mock.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,10 +18,11 @@
//! Test utilities

use ethereum::{TransactionAction, TransactionSignature};
use frame_system::pallet_prelude::BlockNumberFor;
use rlp::RlpStream;
// Substrate
use frame_support::{derive_impl, parameter_types, traits::FindAuthor, ConsensusEngineId};
use sp_core::{hashing::keccak_256, H160, H256, U256};
use sp_core::{hashing::keccak_256, Hasher, H160, H256, U256};
use sp_runtime::{
traits::{Dispatchable, IdentityLookup},
AccountId32, BuildStorage,
Expand Down Expand Up @@ -91,6 +92,17 @@ parameter_types! {
pub const GasLimitStorageGrowthRatio: u64 = BLOCK_GAS_LIMIT.saturating_div(MAX_STORAGE_GROWTH);
}

pub struct RandomnessProvider;
impl frame_support::traits::Randomness<<Test as frame_system::Config>::Hash, BlockNumberFor<Test>>
for RandomnessProvider
{
fn random(subject: &[u8]) -> (<Test as frame_system::Config>::Hash, BlockNumberFor<Test>) {
let output = <Test as frame_system::Config>::Hashing::hash(subject);
let block_number = frame_system::Pallet::<Test>::block_number();
(output, block_number)
}
}

#[derive_impl(pallet_evm::config_preludes::TestDefaultConfig)]
impl pallet_evm::Config for Test {
type AccountProvider = pallet_evm::FrameSystemAccountProvider<Self>;
Expand All @@ -102,6 +114,7 @@ impl pallet_evm::Config for Test {
type FindAuthor = FindAuthorTruncated;
type GasLimitStorageGrowthRatio = GasLimitStorageGrowthRatio;
type Timestamp = Timestamp;
type RandomnessProvider = RandomnessProvider;
}

#[derive_impl(crate::config_preludes::TestDefaultConfig)]
Expand Down
16 changes: 15 additions & 1 deletion frame/evm/precompile/dispatch/src/mock.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,8 @@ use frame_support::{
weights::Weight,
ConsensusEngineId,
};
use sp_core::{H160, H256, U256};
use frame_system::pallet_prelude::BlockNumberFor;
use sp_core::{Hasher, H160, H256, U256};
use sp_runtime::traits::{BlakeTwo256, IdentityLookup};

use fp_evm::{ExitError, ExitReason, Transfer};
Expand Down Expand Up @@ -135,6 +136,18 @@ parameter_types! {
pub WeightPerGas: Weight = Weight::from_parts(20_000, 0);
pub SuicideQuickClearLimit: u32 = 0;
}

pub struct RandomnessProvider;
impl frame_support::traits::Randomness<<Test as frame_system::Config>::Hash, BlockNumberFor<Test>>
for RandomnessProvider
{
fn random(subject: &[u8]) -> (<Test as frame_system::Config>::Hash, BlockNumberFor<Test>) {
let output = <Test as frame_system::Config>::Hashing::hash(subject);
let block_number = frame_system::Pallet::<Test>::block_number();
(output, block_number)
}
}

impl pallet_evm::Config for Test {
type AccountProvider = pallet_evm::FrameSystemAccountProvider<Self>;
type FeeCalculator = FixedGasPrice;
Expand Down Expand Up @@ -162,6 +175,7 @@ impl pallet_evm::Config for Test {
type GasLimitStorageGrowthRatio = ();
type Timestamp = Timestamp;
type WeightInfo = ();
type RandomnessProvider = RandomnessProvider;
}

pub(crate) struct MockHandle {
Expand Down
23 changes: 22 additions & 1 deletion frame/evm/precompile/storage-cleaner/src/mock.rs
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Expand Up @@ -19,9 +19,10 @@

use crate::{StorageCleanerPrecompile, StorageCleanerPrecompileCall};
use frame_support::{parameter_types, weights::Weight};
use frame_system::pallet_prelude::BlockNumberFor;
use pallet_evm::{EnsureAddressNever, EnsureAddressRoot, IdentityAddressMapping};
use precompile_utils::{precompile_set::*, testing::*};
use sp_core::{ConstU32, H256, U256};
use sp_core::{ConstU32, Hasher, H256, U256};
use sp_runtime::{
traits::{BlakeTwo256, IdentityLookup},
BuildStorage,
Expand Down Expand Up @@ -125,6 +126,25 @@ parameter_types! {
pub SuicideQuickClearLimit: u32 = 0;
}

pub struct RandomnessProvider;
impl
frame_support::traits::Randomness<
<Runtime as frame_system::Config>::Hash,
BlockNumberFor<Runtime>,
> for RandomnessProvider
{
fn random(
subject: &[u8],
) -> (
<Runtime as frame_system::Config>::Hash,
BlockNumberFor<Runtime>,
) {
let output = <Runtime as frame_system::Config>::Hashing::hash(subject);
let block_number = frame_system::Pallet::<Runtime>::block_number();
(output, block_number)
}
}

impl pallet_evm::Config for Runtime {
type AccountProvider = pallet_evm::FrameSystemAccountProvider<Self>;
type FeeCalculator = ();
Expand All @@ -149,6 +169,7 @@ impl pallet_evm::Config for Runtime {
type Timestamp = Timestamp;
type WeightInfo = ();
type SuicideQuickClearLimit = SuicideQuickClearLimit;
type RandomnessProvider = RandomnessProvider;
}

/// Build test externalities, prepopulated with data for testing the precompile.
Expand Down
7 changes: 6 additions & 1 deletion frame/evm/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -208,6 +208,12 @@ pub mod pallet {
/// Weight information for extrinsics in this pallet.
type WeightInfo: WeightInfo;

#[pallet::no_default]
type RandomnessProvider: frame_support::traits::Randomness<
sp_core::H256,
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@RomarQ RomarQ Apr 17, 2025

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The runtime implementing this pallet may not what to enabled randomness. (For example, the template runtime which currently has a really dangerous example)

Suggested change
sp_core::H256,
Option<sp_core::H256>,

We can also put this type behind a feature, or just allow the random result to be None.

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@snowmead snowmead Apr 17, 2025 •
edited
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I want to avoid changing this type to Option because I wouldn't be able to pass the randomness pallet directly as an impl since it implements <Hash, ...>. I would have to wrap it.

BlockNumberFor<Self>,
>;

/// EVM config used in the module.
fn config() -> &'static EvmConfig {
&CANCUN_CONFIG
Expand Down Expand Up @@ -701,7 +707,6 @@ pub mod pallet {
.saturating_add(T::DbWeight::get().reads(1))
.saturating_add(account_basic_weight)
.saturating_add(min_gas_weight);

}

total_weight
Expand Down
15 changes: 14 additions & 1 deletion frame/evm/src/mock.rs
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Expand Up @@ -18,7 +18,8 @@
//! Test mock for unit tests and benchmarking

use frame_support::{derive_impl, parameter_types, weights::Weight};
use sp_core::{H160, U256};
use frame_system::pallet_prelude::BlockNumberFor;
use sp_core::{Hasher, H160, U256};

use crate::{
FeeCalculator, IsPrecompileResult, Precompile, PrecompileHandle, PrecompileResult,
Expand Down Expand Up @@ -75,6 +76,18 @@ impl crate::Config for Test {
type Runner = crate::runner::stack::Runner<Self>;
type GasLimitStorageGrowthRatio = GasLimitStorageGrowthRatio;
type Timestamp = Timestamp;
type RandomnessProvider = RandomnessProvider;
}

pub struct RandomnessProvider;
impl frame_support::traits::Randomness<<Test as frame_system::Config>::Hash, BlockNumberFor<Test>>
for RandomnessProvider
{
fn random(subject: &[u8]) -> (<Test as frame_system::Config>::Hash, BlockNumberFor<Test>) {
let output = <Test as frame_system::Config>::Hashing::hash(subject);
let block_number = frame_system::Pallet::<Test>::block_number();
(output, block_number)
}
}

pub struct FixedGasPrice;
Expand Down
8 changes: 7 additions & 1 deletion frame/evm/src/runner/stack.rs
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Expand Up @@ -963,7 +963,13 @@ where
}

fn block_randomness(&self) -> Option<H256> {
None
use frame_support::traits::Randomness;
use scale_codec::Encode;

let current_block = frame_system::Pallet::<T>::block_number();
let output = T::RandomnessProvider::random(&current_block.encode()).0;

Some(output)
}

fn block_gas_limit(&self) -> U256 {
Expand Down
22 changes: 21 additions & 1 deletion precompiles/tests-external/lib.rs
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Expand Up @@ -27,7 +27,7 @@ use std::{cell::RefCell, rc::Rc};
use frame_support::{
construct_runtime, derive_impl, parameter_types, traits::Everything, weights::Weight,
};
use sp_core::{H160, H256, U256};
use sp_core::{Hasher, H160, H256, U256};
use sp_runtime::{
traits::{BlakeTwo256, IdentityLookup},
BuildStorage, Perbill,
Expand Down Expand Up @@ -253,6 +253,26 @@ impl pallet_evm::Config for Runtime {
type GasLimitStorageGrowthRatio = ();
type Timestamp = Timestamp;
type WeightInfo = pallet_evm::weights::SubstrateWeight<Runtime>;
type RandomnessProvider = RandomnessProvider;
}

pub struct RandomnessProvider;
impl
frame_support::traits::Randomness<
<Runtime as frame_system::Config>::Hash,
frame_system::pallet_prelude::BlockNumberFor<Runtime>,
> for RandomnessProvider
{
fn random(
subject: &[u8],
) -> (
<Runtime as frame_system::Config>::Hash,
frame_system::pallet_prelude::BlockNumberFor<Runtime>,
) {
let output = <Runtime as frame_system::Config>::Hashing::hash(subject);
let block_number = frame_system::Pallet::<Runtime>::block_number();
(output, block_number)
}
}

parameter_types! {
Expand Down
24 changes: 23 additions & 1 deletion template/runtime/src/lib.rs
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Expand Up @@ -20,7 +20,7 @@ use sp_consensus_aura::sr25519::AuthorityId as AuraId;
use sp_consensus_grandpa::{AuthorityId as GrandpaId, AuthorityList as GrandpaAuthorityList};
use sp_core::{
crypto::{ByteArray, KeyTypeId},
ConstU128, OpaqueMetadata, H160, H256, U256,
ConstU128, Hasher, OpaqueMetadata, H160, H256, U256,
};
use sp_runtime::{
create_runtime_str, generic, impl_opaque_keys,
Expand Down Expand Up @@ -50,6 +50,7 @@ use sp_genesis_builder::PresetId;
use fp_account::EthereumSignature;
use fp_evm::weight_per_gas;
use fp_rpc::TransactionStatus;
use frame_system::pallet_prelude::BlockNumberFor;
use pallet_ethereum::{Call::transact, PostLogContent, Transaction as EthereumTransaction};
use pallet_evm::{
Account as EVMAccount, EnsureAccountId20, FeeCalculator, IdentityAddressMapping, Runner,
Expand Down Expand Up @@ -336,6 +337,26 @@ impl<F: FindAuthor<u32>> FindAuthor<H160> for FindAuthorTruncated<F> {
}
}

/// WARNING! THIS IS JUST AN EXAMPLE AND SHOULD NOT BE USED AS A MEANS TO RETRIEVE SECURE RANDOMNESS
pub struct RandomnessProvider;
impl
frame_support::traits::Randomness<
<Runtime as frame_system::Config>::Hash,
BlockNumberFor<Runtime>,
> for RandomnessProvider
{
fn random(
subject: &[u8],
) -> (
<Runtime as frame_system::Config>::Hash,
BlockNumberFor<Runtime>,
) {
let output = <Runtime as frame_system::Config>::Hashing::hash(subject);
let block_number = frame_system::Pallet::<Runtime>::block_number();
(output, block_number)
}
}
Comment on lines +341 to +358
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@RomarQ RomarQ Apr 17, 2025

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This example is dangerous and we should change it. Suggestion in a comment above.

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@snowmead snowmead Apr 17, 2025

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I could return a zero hash instead.

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@RomarQ RomarQ Apr 17, 2025

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Ignore my comment, this should be fine. The spec explicit says that this should not be used as a true randomness source.

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@RomarQ RomarQ Apr 17, 2025

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Sorry for coming back to this, could we append pallet_timestamp::Pallet::<Runtime>::now() to the subject.

And also add a note saying This is just an example, this should not be used as a true randomness source


const BLOCK_GAS_LIMIT: u64 = 75_000_000;
const MAX_POV_SIZE: u64 = 5 * 1024 * 1024;
/// The maximum storage growth per block in bytes.
Expand Down Expand Up @@ -374,6 +395,7 @@ impl pallet_evm::Config for Runtime {
type GasLimitStorageGrowthRatio = GasLimitStorageGrowthRatio;
type Timestamp = Timestamp;
type WeightInfo = pallet_evm::weights::SubstrateWeight<Self>;
type RandomnessProvider = RandomnessProvider;
}

parameter_types! {
Expand Down