Couple fixes & minor refactor

evm/src/cpu/kernel/aggregator.rs

@@ -17,6 +17,7 @@ pub(crate) fn combined_kernel() -> Kernel {
         include_str!("asm/core/call.asm"),
         include_str!("asm/core/create.asm"),
         include_str!("asm/core/create_addresses.asm"),
+        include_str!("asm/core/gas.asm"),
         include_str!("asm/core/intrinsic_gas.asm"),
         include_str!("asm/core/invalid.asm"),
         include_str!("asm/core/jumpdest_analysis.asm"),

evm/src/cpu/kernel/asm/core/gas.asm

@@ -0,0 +1,49 @@
+global sys_gas:
+    // stack: kexit_info
+    %charge_gas_const(@GAS_BASE)
+    // stack: kexit_info
+    DUP1 %shr_const(192)
+    // stack: gas_used, kexit_info
+    %ctx_gas_limit
+    // stack: gas_limit, gas_used, kexit_info
+    SUB
+    // stack: gas_remaining, kexit_info
+    SWAP1
+    EXIT_KERNEL
+
+%macro ctx_gas_limit
+    %mload_context_metadata(@CTX_METADATA_GAS_LIMIT)
+%endmacro
+
+// Charge gas. Faults if we exceed the limit for the current context.
+%macro charge_gas
+    // stack: gas, kexit_info
+    %shl_const(192)
+    ADD
+    // stack: kexit_info'
+    %ctx_gas_limit
+    // stack: gas_limit, kexit_info'
+    DUP2 %shr_const(192)
+    // stack: gas_used, gas_limit, kexit_info'
+    GT
+    // stack: out_of_gas, kexit_info'
+    %jumpi(fault_exception)
+    // stack: kexit_info'
+%endmacro
+
+// Charge a constant amount of gas.
+%macro charge_gas_const(gas)
+    // stack: kexit_info
+    PUSH $gas
+    // stack: gas, kexit_info
+    %charge_gas
+    // stack: kexit_info'
+%endmacro
+
+// Charge gas and exit kernel code.
+%macro charge_gas_and_exit
+    // stack: gas, kexit_info
+    %charge_gas
+    // stack: kexit_info'
+    EXIT_KERNEL
+%endmacro

evm/src/cpu/kernel/asm/core/syscall_stubs.asm

@@ -60,16 +60,6 @@ global sys_selfbalance:
     PANIC
 global sys_basefee:
     PANIC
-global sys_gas:
-    // stack: kexit_info
-    DUP1 %shr_const(192)
-    // stack: gas_used, kexit_info
-    %mload_context_metadata(@CTX_METADATA_GAS_LIMIT)
-    // stack: gas_limit, gas_used, kexit_info
-    SUB
-    // stack: gas_remaining, kexit_info
-    SWAP1
-    EXIT_KERNEL
 global sys_log0:
     PANIC
 global sys_log1:

evm/src/cpu/kernel/asm/core/terminate.asm

@@ -37,7 +37,7 @@ global sys_revert:
     PUSH 0 // success
     %jump(terminate_common)
 
-// The execution is in an exceptional halt-ing state if
+// The execution is in an exceptional halting state if
 // - there is insufficient gas
 // - the instruction is invalid
 // - there are insufficient stack items

evm/src/cpu/kernel/asm/curve/secp256k1/ecrecover.asm

@@ -106,19 +106,7 @@ ecdsa_after_precompute_loop_end:
 // Take a public key (PKx, PKy) and return the associated address KECCAK256(PKx || PKy)[-20:].
 pubkey_to_addr:
     // stack: PKx, PKy, retdest
-    PUSH 0
+    %keccak256_u256_pair
-    // stack: 0, PKx, PKy, retdest
-    MSTORE // TODO: switch to kernel memory (like `%mstore_kernel(@SEGMENT_KERNEL_GENERAL)`).
-    // stack: PKy, retdest
-    PUSH 0x20
-    // stack: 0x20, PKy, retdest
-    MSTORE
-    // stack: retdest
-    PUSH 0x40
-    // stack: 0x40, retdest
-    PUSH 0
-    // stack: 0, 0x40, retdest
-    KECCAK256
     // stack: hash, retdest
     PUSH 0xffffffffffffffffffffffffffffffffffffffff
     // stack: 2^160-1, hash, retdest

evm/src/cpu/kernel/asm/memory/metadata.asm

@@ -147,3 +147,16 @@ global sys_msize:
     ADD
     // stack: cost = num_words^2 / 512 + num_words * GAS_MEMORY
 %endmacro
+
+// Faults if the given offset is "unreasonable", i.e. the associated memory expansion cost
+// would exceed any reasonable block limit.
+// We do this to avoid overflows in future gas-related calculations.
+%macro ensure_reasonable_offset
+    // stack: offset
+    // The memory expansion cost, (50000000 / 32)^2 / 512, is around 2^32 gas,
+    // i.e. greater than any reasonable block limit.
+    %gt_const(50000000)
+    // stack: is_unreasonable
+    %jumpi(fault_exception)
+    // stack: (empty)
+%endmacro

evm/src/cpu/kernel/asm/memory/syscalls.asm

@@ -1,4 +1,6 @@
 global sys_mload:
+    // stack: kexit_info, offset
+    DUP2 %ensure_reasonable_offset
     // stack: kexit_info, offset
     %charge_gas_const(@GAS_VERYLOW)
     // stack: kexit_info, offset
@@ -44,6 +46,8 @@ global sys_mload:
     EXIT_KERNEL
 
 global sys_mstore:
+    // stack: kexit_info, offset, value
+    DUP2 %ensure_reasonable_offset
     // stack: kexit_info, offset, value
     %charge_gas_const(@GAS_VERYLOW)
     // stack: kexit_info, offset, value
@@ -87,6 +91,8 @@ global sys_mstore:
     EXIT_KERNEL
 
 global sys_mstore8:
+    // stack: kexit_info, offset, value
+    DUP2 %ensure_reasonable_offset
     // stack: kexit_info, offset, value
     %charge_gas_const(@GAS_VERYLOW)
     // stack: kexit_info, offset, value

evm/src/cpu/kernel/asm/util/basic_macros.asm

@@ -345,28 +345,3 @@
     %endrep
     // stack: a || b || c || d
 %endmacro
-
-// Charge gas.
-%macro charge_gas
-    // stack: gas, kexit_info
-    %shl_const(192)
-    ADD
-    // stack: kexit_info'
-%endmacro
-
-// Charge a constant amount of gas.
-%macro charge_gas_const(gas)
-    // stack: kexit_info
-    PUSH $gas
-    // stack: gas, kexit_info
-    %charge_gas
-    // stack: kexit_info'
-%endmacro
-
-// Charge gas and exit kernel code.
-%macro charge_gas_and_exit
-    // stack: gas, kexit_info
-    %charge_gas
-    // stack: kexit_info'
-    EXIT_KERNEL
-%endmacro

evm/src/cpu/kernel/asm/util/keccak.asm

@@ -23,3 +23,21 @@ global sys_keccak256:
     %stack (offset) -> (0, @SEGMENT_KERNEL_GENERAL, 0, $num_bytes) // context, segment, offset, len
     KECCAK_GENERAL
 %endmacro
+
+// Computes Keccak256(a || b). Clobbers @SEGMENT_KERNEL_GENERAL.
+//
+// Pre stack: a, b
+// Post stack: hash
+%macro keccak256_u256_pair
+    // Since KECCAK_GENERAL takes its input from memory, we will first write
+    // a's bytes to @SEGMENT_KERNEL_GENERAL[0..32], then b's bytes to
+    // @SEGMENT_KERNEL_GENERAL[32..64].
+    %stack (a) -> (0, @SEGMENT_KERNEL_GENERAL, 0, a, 32, %%after_mstore_a)
+    %jump(mstore_unpacking)
+%%after_mstore_a:
+    %stack (offset, b) -> (0, @SEGMENT_KERNEL_GENERAL, 32, b, 32, %%after_mstore_b)
+    %jump(mstore_unpacking)
+%%after_mstore_b:
+    %stack (offset) -> (0, @SEGMENT_KERNEL_GENERAL, 0, 64) // context, segment, offset, len
+    KECCAK_GENERAL
+%endmacro