Check the proof size is a multiple of 60

[mininny]

Description

The Go slow implementation and the Solidity implementation of the RISCV virtual machine are supposed to be equivalent.

The Go slow implementation ensures that the proof size is a multiple of 60.

	proofContentOffset := shortToU64(uint16(stateContentOffset) + paddedStateSize + 32)

	if and(b32asBEWord(calldataload(shortToU64(uint16(stateContentOffset)+paddedStateSize))), shortToU256(60-1)) != (U256{}) {
		// proof offset must be stateContentOffset+paddedStateSize+32
		// proof size: 64-5+1=60 * 32 byte leaf,
		// but multiple memProof can be used, so the proofSize must be a multiple of 60
		panic("invalid proof offset input")
	}

However, the Solidity implementation doesn't check the _proof size.

            if iszero(eq(_proof.offset, add(add(_stateData.offset, paddedLen(stateSize())), 32))) {
                // 132+stateSize+padding+32 = expected proof offset
                revert(0, 0)
            }
            function proofContentOffset() -> out {
                // since we can't reference proof.offset in functions, blame Yul
                // 132+362+(32-362%32)+32=548
                out := 548
            }
            if iszero(eq(_proof.offset, proofContentOffset())) { revert(0, 0) }

The Solidity implementation should implement a check to ensure that the _proof size is a multiple of 32 * 60 as expected.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.89%. Comparing base (8ff9318) to head (e86edbf).
Report is 44 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #99   +/-   ##
=======================================
  Coverage   61.89%   61.89%           
=======================================
  Files          27       27           
  Lines        4091     4091           
=======================================
  Hits         2532     2532           
  Misses       1427     1427           
  Partials      132      132           

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[refcell]

This looks correct to me

[BlocksOnAChain]

@mininny according to the auditors - There is a discrepancy then between Solidity and Slow (as Slow now implementes 32 * 60 in PR101).
Can you please check/solve this, before we merge both PRs?