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Add overflow check in codecopy #444

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Jul 25, 2024
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Add overflow check in codecopy #444

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6 changes: 3 additions & 3 deletions evm_arithmetization/src/cpu/kernel/asm/memory/syscalls.asm
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Original file line number Diff line number Diff line change
Expand Up @@ -316,20 +316,20 @@ mcopy_empty:

PUSH $segment SWAP1
// stack: total_size, segment, src_ctx, kexit_info, dest_offset, offset, size
DUP1 DUP8 DUP8 ADD
DUP1 DUP8 DUP8 %add_or_fault
// stack: offset + size, total_size, total_size, segment, src_ctx, kexit_info, dest_offset, offset, size
LT %jumpi(codecopy_within_bounds)

// stack: total_size, segment, src_ctx, kexit_info, dest_offset, offset, size
DUP7 DUP7 ADD
DUP7 DUP7 ADD // We already checked for overflow.
// stack: offset + size, total_size, segment, src_ctx, kexit_info, dest_offset, offset, size
SUB // extra_size = offset + size - total_size
// stack: extra_size, segment, src_ctx, kexit_info, dest_offset, offset, size
DUP1 DUP8 SUB
// stack: copy_size = size - extra_size, extra_size, segment, src_ctx, kexit_info, dest_offset, offset, size

// Compute the new dest_offset after actual copies, at which we will start padding with zeroes.
DUP1 DUP7 ADD
DUP1 DUP7 ADD // We already checked for overflow.
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(the check is done prior entering codecopy_after_checks)

// stack: new_dest_offset, copy_size, extra_size, segment, src_ctx, kexit_info, dest_offset, offset, size

GET_CONTEXT
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