cannon: Fix inverted hint writing conditional check

[mbaxter]

Description

Fix hint writing logic in mips.go: we should read hints while the accumulated hint data is >= the current hint's length prefix.

Tests

• Add some unit tests around hint writing.
• Update hint writing fuzz test to set random data at the memory range that is being used in the syscall.

Additional context

This is part of the work to address the Coinbase security audit of Cannon.

Metadata

Part of: https://github.com/ethereum-optimism/client-pod/issues/761 (H-01)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 42.35%. Comparing base (3508670) to head (7d53412).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #10514      +/-   ##
===========================================
+ Coverage    42.31%   42.35%   +0.04%     
===========================================
  Files           73       73              
  Lines         4838     4838              
  Branches       766      766              
===========================================
+ Hits          2047     2049       +2     
+ Misses        2682     2681       -1     
+ Partials       109      108       -1     

Flag	Coverage Δ
cannon-go-tests	81.77% <100.00%> (+0.18%)	⬆️
chain-mon-tests	27.14% <ø> (ø)
common-ts-tests	26.72% <ø> (ø)
contracts-ts-tests	12.25% <ø> (ø)
core-utils-tests	44.03% <ø> (ø)
sdk-tests	40.27% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
cannon/mipsevm/mips.go	95.20% <100.00%> (+0.41%)	⬆️
cannon/mipsevm/state.go	87.23% <ø> (ø)

[coderabbitai]

Walkthrough

Walkthrough

The recent updates involve enhancements and modifications across several files in the cannon/mipsevm module. Key changes include the addition of a new test function and a type for hint tracking, adjustments to hint processing logic in syscall handling, and the introduction of randomness in fuzz testing. These changes aim to refine the system's handling of hints and improve testing robustness.

Changes

File(s)	Summary of Changes
.../evm_test.go	Added TestEVMSysWriteHint and hintTrackingOracle type with associated methods.
.../fuzz_evm_test.go	Updated imports and modified FuzzStateHintWrite to use a new randSeed parameter for random data generation.
mips.go, state.go	Changed hint length processing logic in handleSyscall and reading LastHint conditions from >= to <=.

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Recent Review Details

Configuration used: .coderabbit.yml
Review profile: CHILL

Commits

Files that changed from the base of the PR and between 043ee4d and 7d53412.

Files selected for processing (4)

• cannon/mipsevm/evm_test.go (2 hunks)
• cannon/mipsevm/fuzz_evm_test.go (4 hunks)
• cannon/mipsevm/mips.go (1 hunks)
• cannon/mipsevm/state.go (1 hunks)

Additional comments not posted (6)

cannon/mipsevm/state.go (1)

41-41: Change in conditional logic correctly ensures that hints are only processed when the data is sufficient.

cannon/mipsevm/mips.go (1)

126-126: Change in conditional logic correctly ensures that hints are only processed when the data is sufficient.

cannon/mipsevm/fuzz_evm_test.go (2)

4-5: Addition of imports supports new functionality for generating random data in fuzz tests.

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Line range hint 403-425: Enhancements to FuzzStateHintWrite function with randSeed parameter and logic for generating random data improve the robustness of fuzz tests.

cannon/mipsevm/evm_test.go (2)

253-429: The implementation of TestEVMSysWriteHint appears comprehensive and well-structured. It tests various scenarios of hint writing, ensuring robustness in the system's handling of edge cases. The use of hintTrackingOracle to capture the hints for verification is a clever approach, enhancing the test's ability to assert correctness directly.

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575-585: The hintTrackingOracle type is effectively used in tests to track hints. However, the GetPreimage method currently returns nil, which might be intentional for the current tests but could limit the utility of this oracle in scenarios where actual preimage data is needed for more comprehensive testing.

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