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Ensure proper offset + size bounds in wcopy #445

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Jul 26, 2024
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Ensure proper offset + size bounds in wcopy #445

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13 changes: 13 additions & 0 deletions evm_arithmetization/src/cpu/kernel/asm/memory/metadata.asm
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Original file line number Diff line number Diff line change
Expand Up @@ -453,6 +453,19 @@ zero_hash:
// stack: sum
%endmacro

// Adds the two top elements of the stack, and faults in case of overflow modulo 2^32.
%macro add_u32_or_fault
// stack: x, y
%add_or_fault
DUP1
// stack: sum, sum
PUSH 0xffffffff // 2^32 - 1
LT
// stack: is_overflow, sum
%jumpi(fault_exception)
// stack: sum
%endmacro

%macro call_depth
%mload_global_metadata(@GLOBAL_METADATA_CALL_STACK_DEPTH)
%endmacro
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9 changes: 8 additions & 1 deletion evm_arithmetization/src/cpu/kernel/asm/memory/syscalls.asm
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Expand Up @@ -79,7 +79,14 @@ calldataload_large_offset:
// stack: kexit_info, dest_offset, offset, size
%wcopy_charge_gas

%stack (kexit_info, dest_offset, offset, size) -> (dest_offset, size, kexit_info, dest_offset, offset, size)
// Ensure that `offset + size` won't overflow the reserved 32-bit limb
// of the `virtual` component of the source memory address.
DUP4 DUP4
// stack: offset, size, kexit_info, dest_offset, offset, size
%add_u32_or_fault

%stack (offset_plus_size, kexit_info, dest_offset, offset, size) ->
(dest_offset, size, kexit_info, dest_offset, offset, size)
%add_or_fault
// stack: expanded_num_bytes, kexit_info, dest_offset, offset, size, kexit_info
DUP1 %ensure_reasonable_offset
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