wasmtime/crates/environ/fuzz/fuzz_targets/fact-valid-module.rs

//! A simple fuzzer for FACT
//!
//! This is an intentionally small fuzzer which is intended to only really be
//! used during the development of FACT itself when generating adapter modules.
//! This creates arbitrary adapter signatures and then generates the required
//! trampoline for that adapter ensuring that the final output wasm module is a
//! valid wasm module. This doesn't actually validate anything about the
//! correctness of the trampoline, only that it's valid wasm.

#![no_main]

use arbitrary::Arbitrary;
use component_fuzz_util::TestCase;
use libfuzzer_sys::fuzz_target;
use wasmparser::{Parser, Payload, Validator, WasmFeatures};
use wasmtime_environ::component::*;
use wasmtime_environ::fact::Module;

#[derive(Arbitrary, Debug)]
struct GenAdapterModule {
    debug: bool,
    adapters: Vec<GenAdapter>,
}

#[derive(Arbitrary, Debug)]
struct GenAdapter {
    post_return: bool,
    lift_memory64: bool,
    lower_memory64: bool,
    test: TestCase,
}

fuzz_target!(|module: GenAdapterModule| {
    target(module);
});

fn target(module: GenAdapterModule) {
    drop(env_logger::try_init());

    let mut types = ComponentTypesBuilder::default();

    // Manufactures a unique `CoreDef` so all function imports get unique
    // function imports.
    let mut next_def = 0;
    let mut dummy_def = || {
        next_def += 1;
        dfg::CoreDef::Adapter(dfg::AdapterId::from_u32(next_def))
    };

    // Manufactures a `CoreExport` for a memory with the shape specified. Note
    // that we can't import as many memories as functions so these are
    // intentionally limited. Once a handful of memories are generated of each
    // type then they start getting reused.
    let mut next_memory = 0;
    let mut memories32 = Vec::new();
    let mut memories64 = Vec::new();
    let mut dummy_memory = |memory64: bool| {
        let dst = if memory64 {
            &mut memories64
        } else {
            &mut memories32
        };
        let idx = if dst.len() < 5 {
            next_memory += 1;
            dst.push(next_memory - 1);
            next_memory - 1
        } else {
            dst[0]
        };
        dfg::CoreExport {
            instance: dfg::InstanceId::from_u32(idx),
            item: ExportItem::Name(String::new()),
        }
    };

    let mut adapters = Vec::new();
    for adapter in module.adapters.iter() {
        let wat_decls = adapter.test.declarations();
        let wat = format!(
            "(component
                {types}
                (type (func {params} {result}))
            )",
            types = wat_decls.types,
            params = wat_decls.params,
            result = wat_decls.result,
        );
        let wasm = wat::parse_str(&wat).unwrap();

        let mut validator = Validator::new_with_features(WasmFeatures {
            component_model: true,
            ..Default::default()
        });

        types.push_type_scope();
        for payload in Parser::new(0).parse_all(&wasm) {
            let payload = payload.unwrap();
            validator.payload(&payload).unwrap();
            let section = match payload {
                Payload::ComponentTypeSection(s) => s,
                _ => continue,
            };
            for ty in section {
                let ty = types.intern_component_type(&ty.unwrap()).unwrap();
                types.push_component_typedef(ty);
                let ty = match ty {
                    TypeDef::ComponentFunc(ty) => ty,
                    _ => continue,
                };
                adapters.push(Adapter {
                    lift_ty: ty,
                    lower_ty: ty,
                    lower_options: AdapterOptions {
                        instance: RuntimeComponentInstanceIndex::from_u32(0),
                        string_encoding: convert_encoding(adapter.test.encoding1),
                        memory64: adapter.lower_memory64,
                        // Pessimistically assume that memory/realloc are going to be
                        // required for this trampoline and provide it. Avoids doing
                        // calculations to figure out whether they're necessary and
                        // simplifies the fuzzer here without reducing coverage within FACT
                        // itself.
                        memory: Some(dummy_memory(adapter.lower_memory64)),
                        realloc: Some(dummy_def()),
                        // Lowering never allows `post-return`
                        post_return: None,
                    },
                    lift_options: AdapterOptions {
                        instance: RuntimeComponentInstanceIndex::from_u32(1),
                        string_encoding: convert_encoding(adapter.test.encoding2),
                        memory64: adapter.lift_memory64,
                        memory: Some(dummy_memory(adapter.lift_memory64)),
                        realloc: Some(dummy_def()),
                        post_return: if adapter.post_return {
                            Some(dummy_def())
                        } else {
                            None
                        },
                    },
                    func: dummy_def(),
                });
            }
        }
        types.pop_type_scope();
    }

    let types = types.finish();
    let mut fact_module = Module::new(&types, module.debug);
    for (i, adapter) in adapters.iter().enumerate() {
        fact_module.adapt(&format!("adapter{i}"), adapter);
    }
    let wasm = fact_module.encode();
    let result = Validator::new_with_features(WasmFeatures {
        multi_memory: true,
        memory64: true,
        ..WasmFeatures::default()
    })
    .validate_all(&wasm);

    let err = match result {
        Ok(_) => return,
        Err(e) => e,
    };
    eprintln!("invalid wasm module: {err:?}");
    for adapter in module.adapters.iter() {
        eprintln!("adapter: {adapter:?}");
    }
    std::fs::write("invalid.wasm", &wasm).unwrap();
    match wasmprinter::print_bytes(&wasm) {
        Ok(s) => std::fs::write("invalid.wat", &s).unwrap(),
        Err(_) => drop(std::fs::remove_file("invalid.wat")),
    }

    panic!()
}

fn convert_encoding(encoding: component_fuzz_util::StringEncoding) -> StringEncoding {
    match encoding {
        component_fuzz_util::StringEncoding::Utf8 => StringEncoding::Utf8,
        component_fuzz_util::StringEncoding::Utf16 => StringEncoding::Utf16,
        component_fuzz_util::StringEncoding::Latin1OrUtf16 => StringEncoding::CompactUtf16,
    }
}