Merge pull request #844 from wasmx/metering

Support metering cost for memory pages
wasmx · Mar 3, 2023 · b9e1c18 · b9e1c18
2 parents 6b39221 + a5e1e4e
commit b9e1c18
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Showing 3 changed files with 38 additions and 2 deletions.
diff --git a/lib/fizzy/execute.cpp b/lib/fizzy/execute.cpp
@@ -898,8 +898,15 @@ ExecutionResult execute(
         }
         case Instr::memory_grow:
         {
-            stack.top() =
-                grow_memory(*memory, stack.top().as<uint32_t>(), instance.memory_pages_limit);
+            const auto delta_pages = stack.top().as<uint32_t>();
+
+            if constexpr (MeteringEnabled)
+            {
+                if ((ctx.ticks -= get_grow_memory_cost(delta_pages)) < 0)
+                    goto trap;
+            }
+
+            stack.top() = grow_memory(*memory, delta_pages, instance.memory_pages_limit);
             break;
         }
         case Instr::i32_const:

diff --git a/lib/fizzy/instructions.hpp b/lib/fizzy/instructions.hpp
@@ -31,4 +31,10 @@ const uint8_t* get_instruction_max_align_table() noexcept;
 /// execution metering.
 const int16_t* get_instruction_cost_table() noexcept;
 
+/// Calculates the cost of memory expansion. Currently set at 65536 per page (1 per byte).
+inline constexpr auto get_grow_memory_cost(uint32_t delta_pages) noexcept
+{
+    return delta_pages * 65536;
+}
+
 }  // namespace fizzy
diff --git a/test/unittests/execute_test.cpp b/test/unittests/execute_test.cpp
@@ -1101,3 +1101,26 @@ TEST(execute, metering)
     ctx.ticks = 0;
     EXPECT_THAT(execute(*instance, 0, {}, ctx), Traps());
 }
+
+TEST(execute, metering_memory)
+{
+    /* wat2wasm
+    (memory 0 1)
+    (func (result i32)
+      i32.const 1
+      memory.grow
+    )
+    */
+    const auto wasm =
+        from_hex("0061736d010000000105016000017f030201000504010100010a08010600410140000b");
+    auto instance = instantiate(parse(wasm));
+
+    ExecutionContext ctx;
+    ctx.metering_enabled = true;
+    ctx.ticks = 100000;
+    EXPECT_THAT(execute(*instance, 0, {}, ctx), Result(0));
+    EXPECT_EQ(ctx.ticks, 34461);
+
+    ctx.ticks = 65536;
+    EXPECT_THAT(execute(*instance, 0, {}, ctx), Traps());
+}