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Fix modexp record gas #1290

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Fix modexp record gas #1290

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0c759e2
fix modexp record gas
zjb0807 Jan 25, 2024
056ef7c
fix clippy
zjb0807 Jan 26, 2024
0832c44
fix
zjb0807 Jan 28, 2024
344f542
format
zjb0807 Jan 28, 2024
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67 changes: 38 additions & 29 deletions frame/evm/precompile/modexp/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -172,14 +172,6 @@ impl Precompile for Modexp {
let exp_len = exp_len_big.to_usize().expect("exp_len out of bounds");
let mod_len = mod_len_big.to_usize().expect("mod_len out of bounds");

// if mod_len is 0 output must be empty
if mod_len == 0 {
return Ok(PrecompileOutput {
exit_status: ExitSucceed::Returned,
output: vec![],
});
}

// Gas formula allows arbitrary large exp_len when base and modulus are empty, so we need to handle empty base first.
let r = if base_len == 0 && mod_len == 0 {
handle.record_cost(MIN_GAS_COST)?;
Expand Down Expand Up @@ -235,8 +227,9 @@ impl Precompile for Modexp {
output: ret.to_vec(),
})
} else {
Err(PrecompileFailure::Error {
exit_status: ExitError::Other("failed".into()),
Ok(PrecompileOutput {
exit_status: ExitSucceed::Returned,
output: vec![],
})
Comment on lines 229 to 233
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This case seems unclear to me, it's basically when bytes.len() > mod_len, which shouldn't be possible except for this case of mod_len == 0. Maybe this is better written by handling that case specifically rather than assume it is the case in the final catch-all } else { block.

Also see the comment above this (line ~ 215) which is relevant:

// always true except in the case of zero-length modulus, which leads to
// output of length and value 1.

This seems to contradict the expectation of returning an empty vec.

}
}
Expand All @@ -255,11 +248,35 @@ mod tests {
Ok(())
}

#[test]
fn test_min_gas() {
let context: Context = Context {
address: Default::default(),
caller: Default::default(),
apparent_value: From::from(0),
};

assert_eq!(
Modexp::execute(&mut MockHandle::new(vec![], Some(199), context.clone())),
Err(PrecompileFailure::Error {
exit_status: ExitError::OutOfGas,
})
);

assert_eq!(
Modexp::execute(&mut MockHandle::new(vec![], Some(200), context)),
Ok(PrecompileOutput {
exit_status: ExitSucceed::Returned,
output: vec![],
})
);
}

#[test]
fn test_empty_input() {
let input = Vec::new();

let cost: u64 = 1;
let cost: u64 = 200;

let context: Context = Context {
address: Default::default(),
Expand Down Expand Up @@ -288,7 +305,7 @@ mod tests {
)
.expect("Decode failed");

let cost: u64 = 1;
let cost: u64 = 10000;

let context: Context = Context {
address: Default::default(),
Expand All @@ -310,15 +327,15 @@ mod tests {
}

#[test]
fn test_excessive_input() -> Result<(), PrecompileFailure> {
fn test_excessive_input() {
let input = hex::decode(
"1000000000000000000000000000000000000000000000000000000000000001\
0000000000000000000000000000000000000000000000000000000000000001\
0000000000000000000000000000000000000000000000000000000000000001",
)
.expect("Decode failed");

let cost: u64 = 1;
let cost: u64 = 200;

let context: Context = Context {
address: Default::default(),
Expand All @@ -328,20 +345,12 @@ mod tests {

let mut handle = MockHandle::new(input, Some(cost), context);

match Modexp::execute(&mut handle) {
Ok(_) => {
panic!("Test not expected to pass");
}
Err(e) => {
assert_eq!(
e,
PrecompileFailure::Error {
exit_status: ExitError::Other("unreasonably large base length".into())
}
);
Ok(())
}
}
assert_eq!(
Modexp::execute(&mut handle),
Err(PrecompileFailure::Error {
exit_status: ExitError::Other("unreasonably large base length".into())
})
);
}

#[test]
Expand Down Expand Up @@ -515,7 +524,7 @@ mod tests {
apparent_value: From::from(0),
};

let mut handle = MockHandle::new(input, Some(100_000), context);
let mut handle = MockHandle::new(input, Some(1_000_000), context);

let _ = Modexp::execute(&mut handle).expect("Modexp::execute() returned error");

Expand Down
10 changes: 8 additions & 2 deletions frame/evm/test-vector-support/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -77,6 +77,12 @@ impl PrecompileHandle for MockHandle {

fn record_cost(&mut self, cost: u64) -> Result<(), ExitError> {
self.gas_used += cost;

if let Some(gas_limit) = self.gas_limit {
if self.gas_used > gas_limit {
return Err(ExitError::OutOfGas);
}
}
Ok(())
}

Expand Down Expand Up @@ -132,7 +138,7 @@ pub fn test_precompile_test_vectors<P: Precompile>(filepath: &str) -> Result<(),
for test in tests {
let input: Vec<u8> = hex::decode(test.input).expect("Could not hex-decode test input data");

let cost: u64 = 10000000;
let cost: u64 = 100000000;

let context: Context = Context {
address: Default::default(),
Expand Down Expand Up @@ -184,7 +190,7 @@ pub fn test_precompile_failure_test_vectors<P: Precompile>(filepath: &str) -> Re
for test in tests {
let input: Vec<u8> = hex::decode(test.input).expect("Could not hex-decode test input data");

let cost: u64 = 10000000;
let cost: u64 = 100000000;

let context: Context = Context {
address: Default::default(),
Expand Down
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