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[feat] make assembly block Solidity memory safe #50

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Oct 30, 2023
Merged

[feat] make assembly block Solidity memory safe #50

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8 changes: 7 additions & 1 deletion snark-verifier/src/loader/evm/code.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,13 @@ pragma solidity ^0.8.0;

contract Halo2Verifier {{
fallback(bytes calldata) external returns (bytes memory) {{
assembly {{
assembly (\"memory-safe\") {{
// Enforce that Solidity memory layout is respected
let data := mload(0x40)
if iszero(eq(data, 0x80)) {{
revert(0, 0)
}}

let success := true
let f_p := {base_modulus}
let f_q := {scalar_modulus}
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5 changes: 4 additions & 1 deletion snark-verifier/src/loader/evm/loader.rs
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Expand Up @@ -22,6 +22,9 @@ use std::{
rc::Rc,
};

/// Memory pointer starts at 0x80, which is the end of the Solidity memory layout scratch space.
pub const MEM_PTR_START: usize = 0x80;

#[derive(Clone, Debug)]
pub enum Value<T> {
Constant(T),
Expand Down Expand Up @@ -77,7 +80,7 @@ impl EvmLoader {
base_modulus,
scalar_modulus,
code: RefCell::new(code),
ptr: Default::default(),
ptr: RefCell::new(MEM_PTR_START),
cache: Default::default(),
})
}
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11 changes: 8 additions & 3 deletions snark-verifier/src/system/halo2/transcript/evm.rs
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Expand Up @@ -2,7 +2,12 @@

use crate::{
loader::{
evm::{loader::Value, u256_to_fe, util::MemoryChunk, EcPoint, EvmLoader, Scalar, U256},
evm::{
loader::{Value, MEM_PTR_START},
u256_to_fe,
util::MemoryChunk,
EcPoint, EvmLoader, Scalar, U256,
},
native::{self, NativeLoader},
Loader,
},
Expand Down Expand Up @@ -40,7 +45,7 @@ where
/// u256 for `transcript_initial_state`.
pub fn new(loader: &Rc<EvmLoader>) -> Self {
let ptr = loader.allocate(0x20);
assert_eq!(ptr, 0);
assert_eq!(ptr, MEM_PTR_START);
let mut buf = MemoryChunk::new(ptr);
buf.extend(0x20);
Self {
Expand Down Expand Up @@ -118,7 +123,7 @@ where

fn common_scalar(&mut self, scalar: &Scalar) -> Result<(), Error> {
match scalar.value() {
Value::Constant(_) if self.buf.ptr() == 0 => {
Value::Constant(_) if self.buf.ptr() == MEM_PTR_START => {
self.loader.copy_scalar(scalar, self.buf.ptr());
}
Value::Memory(ptr) => {
Expand Down
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