Add WASM base execution unit

radix-engine/src/vm/wasm_runtime/scrypto_runtime.rs

@@ -1,3 +1,5 @@
+use core::u32;
+
 use crate::errors::InvokeError;
 use crate::errors::RuntimeError;
 use crate::internal_prelude::*;
@@ -21,6 +23,7 @@ pub struct ScryptoRuntime<'y, Y: SystemApi<RuntimeError>> {
     export_name: String,
     wasm_execution_units_buffer: u32,
     scrypto_vm_version: ScryptoVmVersion,
+    wasm_execution_units_base: u32,
 }
 
 impl<'y, Y: SystemApi<RuntimeError>> ScryptoRuntime<'y, Y> {
@@ -30,6 +33,18 @@ impl<'y, Y: SystemApi<RuntimeError>> ScryptoRuntime<'y, Y> {
         export_name: String,
         scrypto_vm_version: ScryptoVmVersion,
     ) -> Self {
+        let wasm_execution_units_base = if scrypto_vm_version < ScryptoVmVersion::cuttlefish() {
+            0
+        } else {
+            // Add 6,000 base units to make sure the we do not undercharge for WASM execution,
+            // which might lead to system exploitation.
+            // This is especially important in corner-cases such as `costing::spin_loop_v2` benchmark.
+            // Use larger cost unit buffer to call `consume_wasm_execution_exceeding_buffer`
+            // less frequently.
+            // 6000
+            6000
+        };
+
         ScryptoRuntime {
             api,
             buffers: index_map_new(),
@@ -38,6 +53,7 @@ impl<'y, Y: SystemApi<RuntimeError>> ScryptoRuntime<'y, Y> {
             export_name,
             wasm_execution_units_buffer: 0,
             scrypto_vm_version,
+            wasm_execution_units_base,
         }
     }
 
@@ -401,6 +417,10 @@ impl<'y, Y: SystemApi<RuntimeError>> WasmRuntime for ScryptoRuntime<'y, Y> {
         &mut self,
         n: u32,
     ) -> Result<(), InvokeError<WasmRuntimeError>> {
+        let n = n
+            .checked_add(self.wasm_execution_units_base)
+            .unwrap_or(u32::MAX);
+
         if n <= self.wasm_execution_units_buffer {
             self.wasm_execution_units_buffer -= n;
             Ok(())