From ed6a657ee188e30dceb1da16960ce2ebd92bf6e8 Mon Sep 17 00:00:00 2001
From: Robin Salen <30937548+Nashtare@users.noreply.github.com>
Date: Thu, 25 Jul 2024 08:55:48 -0400
Subject: [PATCH] Add overflow check in codecopy (#444)

---
 evm_arithmetization/src/cpu/kernel/asm/memory/syscalls.asm | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/evm_arithmetization/src/cpu/kernel/asm/memory/syscalls.asm b/evm_arithmetization/src/cpu/kernel/asm/memory/syscalls.asm
index de04c111e..e3f43a9e1 100644
--- a/evm_arithmetization/src/cpu/kernel/asm/memory/syscalls.asm
+++ b/evm_arithmetization/src/cpu/kernel/asm/memory/syscalls.asm
@@ -316,12 +316,12 @@ 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
@@ -329,7 +329,7 @@ mcopy_empty:
     // 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.
     // stack: new_dest_offset, copy_size, extra_size, segment, src_ctx, kexit_info, dest_offset, offset, size
 
     GET_CONTEXT