Add a new oom fuzz target that runs Wasm and checks it handles OOM

fuzz/Cargo.toml

@@ -30,6 +30,7 @@ pulley-interpreter-fuzz = { workspace = true }
 smallvec = { workspace = true }
 wasmparser = { workspace = true }
 wasmtime = { workspace = true, features = ["winch"] }
+wasmtime-core = { workspace = true }
 wasmtime-fuzzing = { workspace = true }
 wasmtime-test-util = { workspace = true }
 log = { workspace = true }
@@ -126,3 +127,9 @@ path = "fuzz_targets/gc_ops.rs"
 test = false
 doc = false
 bench = false
+
+[[bin]]
+name = "oom"
+path = "fuzz_targets/oom.rs"
+test = false
+doc = false

fuzz/fuzz_targets/oom.rs

@@ -0,0 +1,146 @@
+#![no_main]
+
+use libfuzzer_sys::arbitrary::{Arbitrary, Result, Unstructured};
+use wasmtime::{Engine, Module, Store, Trap, Val, error::OutOfMemory};
+use wasmtime_core::alloc::TryVec;
+use wasmtime_fuzzing::generators::Config;
+use wasmtime_fuzzing::oom::{OomTest, OomTestAllocator};
+use wasmtime_fuzzing::oracles::dummy;
+use wasmtime_fuzzing::single_module_fuzzer::KnownValid;
+
+const OOM_TEST_ITERS: u32 = 10;
+const OOM_TEST_FUEL: u64 = 1000;
+
+#[global_allocator]
+static GLOBAL_ALLOCATOR: OomTestAllocator = OomTestAllocator::new();
+
+wasmtime_fuzzing::single_module_fuzzer!(execute gen_module);
+
+#[derive(Debug)]
+struct OomInput {
+    config: Config,
+    seed: u64,
+}
+
+impl<'a> Arbitrary<'a> for OomInput {
+    fn arbitrary(u: &mut Unstructured<'a>) -> Result<Self> {
+        let mut config: Config = u.arbitrary()?;
+        config.module_config.config.exceptions_enabled = false;
+        config.module_config.config.gc_enabled = false;
+        config.module_config.config.reference_types_enabled = false;
+        config.module_config.function_references_enabled = false;
+        config.module_config.config.export_everything = true;
+        config.wasmtime.strategy =
+            wasmtime_fuzzing::generators::InstanceAllocationStrategy::OnDemand;
+        let seed = u.arbitrary()?;
+        Ok(OomInput { config, seed })
+    }
+}
+
+fn compile(config: &Config, wasm: &[u8]) -> wasmtime::Result<Vec<u8>> {
+    let mut wasmtime_config = config.to_wasmtime();
+    wasmtime_config.concurrency_support(false);
+    wasmtime_config.consume_fuel(true);
+    let engine = Engine::new(&wasmtime_config)?;
+    let module = Module::new(&engine, wasm)?;
+    module.serialize()
+}
+
+fn execute(
+    module: &[u8],
+    _known_valid: KnownValid,
+    input: OomInput,
+    _u: &mut Unstructured<'_>,
+) -> Result<()> {
+    if cfg!(not(arc_try_new)) {
+        panic!(
+            "The OOM fuzzer is disabled because `cfg(arc_try_new)` was not enabled. Build with \
+             `RUSTFLAGS=--cfg=arc_try_new` to enable."
+        );
+    }
+
+    let module_bytes = match compile(&input.config, module) {
+        Ok(bytes) => bytes,
+        Err(_) => return Ok(()),
+    };
+
+    let mut oom_config = input.config.to_wasmtime();
+    oom_config.enable_compiler(false);
+    oom_config.concurrency_support(false);
+    oom_config.consume_fuel(true);
+
+    // Prevent real process-level OOM: fuzzer-generated configs can set
+    // `memory_reservation(0)`, forcing `mmap` to commit real pages that bypass
+    // `OomTestAllocator`. Use large virtual reservations instead.
+    oom_config.memory_reservation(1 << 32);
+    oom_config.memory_guard_size(1 << 31);
+
+    let oom_engine = match Engine::new(&oom_config) {
+        Ok(e) => e,
+        Err(_) => return Ok(()),
+    };
+
+    let _ = OomTest::new()
+        .seed(input.seed)
+        .max_iters(OOM_TEST_ITERS)
+        .allow_alloc_after_oom(true)
+        .alloc_succeeds_after_oom(true)
+        .allow_missed_oom_errors(true)
+        .fuzz(|| {
+            let module = unsafe { Module::deserialize(&oom_engine, &module_bytes)? };
+
+            let mut store = Store::try_new(&oom_engine, ())?;
+            store.set_fuel(OOM_TEST_FUEL).unwrap();
+
+            let linker = dummy::dummy_linker(&mut store, &module)?;
+            let instance = linker.instantiate(&mut store, &module)?;
+
+            'export_loop: for export in module.exports() {
+                let extern_ty = export.ty();
+                let Some(func_ty) = extern_ty.func() else {
+                    continue;
+                };
+                let func = instance.get_func(&mut store, export.name()).unwrap();
+
+                // Build default params; skip if any param type has no default.
+                let mut params: TryVec<Val> = TryVec::with_capacity(func_ty.params().len())?;
+                for p in func_ty.params() {
+                    match p.default_value() {
+                        Some(v) => params.push(v)?,
+                        None => {
+                            continue 'export_loop;
+                        }
+                    }
+                }
+
+                let mut results: TryVec<Val> = TryVec::with_capacity(func_ty.results().len())?;
+                for _ in 0..func_ty.results().len() {
+                    results.push(Val::I32(0))?;
+                }
+
+                match func.call(&mut store, &params, &mut results) {
+                    // OOM; return from this OOM test iteration.
+                    Err(e) if e.is::<OutOfMemory>() => return Err(e),
+
+                    // Out of fuel; stop calling exports.
+                    Err(e)
+                        if e.downcast_ref::<Trap>()
+                            .is_some_and(|trap| *trap == Trap::OutOfFuel) =>
+                    {
+                        break;
+                    }
+
+                    Err(_) | Ok(_) => {}
+                }
+            }
+
+            Ok(())
+        });
+
+    Ok(())
+}
+
+fn gen_module(input: &mut OomInput, u: &mut Unstructured<'_>) -> Result<(Vec<u8>, KnownValid)> {
+    let module = input.config.generate(u, Some(1000))?;
+    Ok((module.to_bytes(), KnownValid::Yes))
+}