From 005f38438243da050e5bb49498bdc324cd728ed9 Mon Sep 17 00:00:00 2001
From: Robin Salen <30937548+Nashtare@users.noreply.github.com>
Date: Thu, 25 Jul 2024 08:56:00 -0400
Subject: [PATCH] Check for overflow in `context_id` increment (#443)

* Range-check context increment

* Doc
---
 evm_arithmetization/src/cpu/kernel/asm/core/util.asm | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/evm_arithmetization/src/cpu/kernel/asm/core/util.asm b/evm_arithmetization/src/cpu/kernel/asm/core/util.asm
index 6b48428ef..26478d0da 100644
--- a/evm_arithmetization/src/cpu/kernel/asm/core/util.asm
+++ b/evm_arithmetization/src/cpu/kernel/asm/core/util.asm
@@ -12,6 +12,17 @@
     // stack: (empty)
     %mload_global_metadata(@GLOBAL_METADATA_LARGEST_CONTEXT)
     %add_const(0x10000000000000000) // scale each context by 2^64
+    // stack: new_ctx
+    DUP1
+
+    // Memory addresses are represented as `ctx.2^64 + segment.2^32 + offset`,
+    // each address component expected to fit in a 32-bit limb.
+    // We enforce here that the new context id won't overflow.
+    PUSH 0xffffffffffffffffffffffff // 2^96 - 1
+    // stack: max, new_ctx, new_ctx
+    LT
+    %jumpi(fault_exception)
+
     // stack: new_ctx
     DUP1
     %mstore_global_metadata(@GLOBAL_METADATA_LARGEST_CONTEXT)