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Throw out fewer fuzz inputs with differential fuzzer (#4859)

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* Throw out fewer fuzz inputs with differential fuzzer

Prior to this commit the differential fuzzer would generate a module and
then select an engine to execute the module against Wasmtime. This
meant, however, that the candidate list of engines were filtered against
the configuration used to generate the module to ensure that the
selected engine could run the generated module.

This commit inverts this logic and instead selects an engine first,
allowing the engine to then tweak the module configuration to ensure
that the generated module is compatible with the engine selected. This
means that fewer fuzz inputs are discarded because every fuzz input will
result in an engine being executed.

Internally the engine constructors have all been updated to update the
configuration to work instead of filtering the configuration. Some other
fixes were applied for the spec interpreter as well to work around #4852

* Fix tests
This commit is contained in:
Alex Crichton
2022-09-06 12:41:23 -05:00
committed by GitHub
parent 9856664f1f
commit 543a487939
8 changed files with 142 additions and 182 deletions
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6
crates/fuzzing/src/generators/config.rs
View File

@@ -38,11 +38,11 @@ impl Config {
// Make it more likely that there are types available to generate a
// function with.
config.min_types = 1;
config.min_types = config.min_types.max(1);
config.max_types = config.max_types.max(1);
// Generate at least one function
config.min_funcs = 1;
config.min_funcs = config.min_funcs.max(1);
config.max_funcs = config.max_funcs.max(1);
// Allow a memory to be generated, but don't let it get too large.
@@ -102,7 +102,7 @@ impl Config {
/// to ensure termination; as doing so will add an additional global to the module,
/// the pooling allocator, if configured, will also have its globals limit updated.
pub fn generate(
&mut self,
&self,
input: &mut Unstructured<'_>,
default_fuel: Option<u32>,
) -> arbitrary::Result<wasm_smith::Module> {

12
crates/fuzzing/src/generators/single_inst_module.rs
View File

@@ -24,17 +24,7 @@ pub struct SingleInstModule<'a> {
impl<'a> SingleInstModule<'a> {
/// Choose a single-instruction module that matches `config`.
pub fn new(u: &mut Unstructured<'a>, config: &mut ModuleConfig) -> arbitrary::Result<&'a Self> {
// To avoid skipping modules unnecessarily during fuzzing, fix up the
// `ModuleConfig` to match the inherent limits of a single-instruction
// module.
config.config.min_funcs = 1;
config.config.max_funcs = 1;
config.config.min_tables = 0;
config.config.max_tables = 0;
config.config.min_memories = 0;
config.config.max_memories = 0;
pub fn new(u: &mut Unstructured<'a>, config: &ModuleConfig) -> arbitrary::Result<&'a Self> {
// Only select instructions that match the `ModuleConfig`.
let instructions = &INSTRUCTIONS
.iter()

41
crates/fuzzing/src/oracles/diff_spec.rs
View File

@@ -1,9 +1,9 @@
//! Evaluate an exported Wasm function using the WebAssembly specification
//! reference interpreter.
use crate::generators::{DiffValue, DiffValueType, ModuleConfig};
use crate::generators::{Config, DiffValue, DiffValueType};
use crate::oracles::engine::{DiffEngine, DiffInstance};
use anyhow::{anyhow, bail, Error, Result};
use anyhow::{anyhow, Error, Result};
use wasm_spec_interpreter::Value;
use wasmtime::Trap;
@@ -11,20 +11,15 @@ use wasmtime::Trap;
pub struct SpecInterpreter;
impl SpecInterpreter {
/// Build a new [`SpecInterpreter`] but only if the configuration does not
/// rely on features that the current bindings (i.e.,
/// `wasm-spec-interpreter`) do not support.
pub fn new(config: &ModuleConfig) -> Result<Self> {
if config.config.reference_types_enabled {
bail!("the spec interpreter bindings do not support reference types")
}
pub(crate) fn new(config: &mut Config) -> Self {
let config = &mut config.module_config.config;
// TODO: right now the interpreter bindings only execute the first
// function in the module so if there's possibly more than one function
// it's not possible to run the other function. This should be fixed
// with improvements to the ocaml bindings to the interpreter.
if config.config.max_funcs > 1 {
bail!("the spec interpreter bindings can only support one function for now")
}
config.min_funcs = 1;
config.max_funcs = 1;
// TODO: right now the instantiation step for the interpreter does
// nothing and the evaluation step performs an instantiation followed by
@@ -32,18 +27,18 @@ impl SpecInterpreter {
// engines will "succeed" in the interpreter because the error is
// delayed to the execution. This should be fixed by making
// instantiation a first-class primitive in our interpreter bindings.
if config.config.max_tables > 0 {
bail!("the spec interpreter bindings do not fail as they should with out-of-bounds table accesses")
}
config.min_tables = 0;
config.max_tables = 0;
if config.config.memory64_enabled {
bail!("memory64 not implemented in spec interpreter");
}
config.min_memories = config.min_memories.min(1);
config.max_memories = config.max_memories.min(1);
if config.config.threads_enabled {
bail!("spec interpreter does not support the threading proposal");
}
Ok(Self)
config.memory64_enabled = false;
config.threads_enabled = false;
config.bulk_memory_enabled = false;
config.reference_types_enabled = false;
Self
}
}
@@ -160,5 +155,5 @@ fn smoke() {
if !wasm_spec_interpreter::support_compiled_in() {
return;
}
crate::oracles::engine::smoke_test_engine(|config| SpecInterpreter::new(&config.module_config))
crate::oracles::engine::smoke_test_engine(|_, config| Ok(SpecInterpreter::new(config)))
}

25
crates/fuzzing/src/oracles/diff_v8.rs
View File

@@ -1,4 +1,4 @@
use crate::generators::{DiffValue, DiffValueType, ModuleConfig};
use crate::generators::{Config, DiffValue, DiffValueType};
use crate::oracles::engine::{DiffEngine, DiffInstance};
use anyhow::{bail, Error, Result};
use std::cell::RefCell;
@@ -12,7 +12,7 @@ pub struct V8Engine {
}
impl V8Engine {
pub fn new(config: &ModuleConfig) -> Result<V8Engine> {
pub fn new(config: &mut Config) -> V8Engine {
static INIT: Once = Once::new();
INIT.call_once(|| {
@@ -21,27 +21,22 @@ impl V8Engine {
v8::V8::initialize();
});
let config = &mut config.module_config.config;
// FIXME: reference types are disabled for now as we seemingly keep finding
// a segfault in v8. This is found relatively quickly locally and keeps
// getting found by oss-fuzz and currently we don't think that there's
// really much we can do about it. For the time being disable reference
// types entirely. An example bug is
// https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=45662
if config.config.reference_types_enabled {
bail!("reference types are buggy in v8");
}
config.reference_types_enabled = false;
if config.config.memory64_enabled {
bail!("memory64 not enabled by default in v8");
}
config.min_memories = config.min_memories.min(1);
config.max_memories = config.max_memories.min(1);
config.memory64_enabled = false;
if config.config.max_memories > 1 {
bail!("multi-memory not enabled by default in v8");
}
Ok(Self {
Self {
isolate: Rc::new(RefCell::new(v8::Isolate::new(Default::default()))),
})
}
}
}
@@ -325,5 +320,5 @@ fn get_diff_value(
#[test]
fn smoke() {
crate::oracles::engine::smoke_test_engine(|config| V8Engine::new(&config.module_config))
crate::oracles::engine::smoke_test_engine(|_, config| Ok(V8Engine::new(config)))
}

53
crates/fuzzing/src/oracles/diff_wasmi.rs
View File

@@ -1,45 +1,30 @@
//! Evaluate an exported Wasm function using the wasmi interpreter.
use crate::generators::{DiffValue, DiffValueType, ModuleConfig};
use crate::generators::{Config, DiffValue, DiffValueType};
use crate::oracles::engine::{DiffEngine, DiffInstance};
use anyhow::{bail, Context, Error, Result};
use anyhow::{Context, Error, Result};
use wasmtime::{Trap, TrapCode};
/// A wrapper for `wasmi` as a [`DiffEngine`].
pub struct WasmiEngine;
impl WasmiEngine {
/// Build a new [`WasmiEngine`] but only if the configuration does not rely
/// on features that `wasmi` does not support.
pub fn new(config: &ModuleConfig) -> Result<Self> {
if config.config.reference_types_enabled {
bail!("wasmi does not support reference types")
}
if config.config.simd_enabled {
bail!("wasmi does not support SIMD")
}
if config.config.multi_value_enabled {
bail!("wasmi does not support multi-value")
}
if config.config.saturating_float_to_int_enabled {
bail!("wasmi does not support saturating float-to-int conversions")
}
if config.config.sign_extension_enabled {
bail!("wasmi does not support sign-extension")
}
if config.config.memory64_enabled {
bail!("wasmi does not support memory64");
}
if config.config.bulk_memory_enabled {
bail!("wasmi does not support bulk memory");
}
if config.config.threads_enabled {
bail!("wasmi does not support threads");
}
if config.config.max_memories > 1 {
bail!("wasmi does not support multi-memory");
}
Ok(Self)
pub(crate) fn new(config: &mut Config) -> Self {
let config = &mut config.module_config.config;
config.reference_types_enabled = false;
config.simd_enabled = false;
config.multi_value_enabled = false;
config.saturating_float_to_int_enabled = false;
config.sign_extension_enabled = false;
config.memory64_enabled = false;
config.bulk_memory_enabled = false;
config.threads_enabled = false;
config.max_memories = config.max_memories.min(1);
config.min_memories = config.min_memories.min(1);
config.max_tables = config.max_tables.min(1);
config.min_tables = config.min_tables.min(1);
Self
}
}
@@ -223,5 +208,5 @@ impl Into<DiffValue> for wasmi::RuntimeValue {
#[test]
fn smoke() {
crate::oracles::engine::smoke_test_engine(|config| WasmiEngine::new(&config.module_config))
crate::oracles::engine::smoke_test_engine(|_, config| Ok(WasmiEngine::new(config)))
}

15
crates/fuzzing/src/oracles/diff_wasmtime.rs
View File

@@ -1,15 +1,16 @@
//! Evaluate an exported Wasm function using Wasmtime.
use crate::generators::{self, DiffValue, DiffValueType};
use crate::generators::{self, DiffValue, DiffValueType, WasmtimeConfig};
use crate::oracles::dummy;
use crate::oracles::engine::DiffInstance;
use crate::oracles::{compile_module, engine::DiffEngine, StoreLimits};
use anyhow::{Context, Error, Result};
use arbitrary::Unstructured;
use wasmtime::{Extern, FuncType, Instance, Module, Store, Trap, TrapCode, Val};
/// A wrapper for using Wasmtime as a [`DiffEngine`].
pub struct WasmtimeEngine {
pub(crate) config: generators::Config,
config: generators::Config,
}
impl WasmtimeEngine {
@@ -17,7 +18,13 @@ impl WasmtimeEngine {
/// later. Ideally the store and engine could be built here but
/// `compile_module` takes a [`generators::Config`]; TODO re-factor this if
/// that ever changes.
pub fn new(config: generators::Config) -> Result<Self> {
pub fn new(u: &mut Unstructured<'_>, config: &generators::Config) -> arbitrary::Result<Self> {
let mut new_config = u.arbitrary::<WasmtimeConfig>()?;
new_config.make_compatible_with(&config.wasmtime);
let config = generators::Config {
wasmtime: new_config,
module_config: config.module_config.clone(),
};
Ok(Self { config })
}
}
@@ -220,5 +227,5 @@ impl Into<DiffValue> for Val {
#[test]
fn smoke() {
crate::oracles::engine::smoke_test_engine(|config| WasmtimeEngine::new(config))
crate::oracles::engine::smoke_test_engine(|u, config| WasmtimeEngine::new(u, config))
}

97
crates/fuzzing/src/oracles/engine.rs
View File

@@ -1,68 +1,37 @@
//! Define the interface for differential evaluation of Wasm functions.
use crate::generators::{Config, DiffValue, DiffValueType, WasmtimeConfig};
use crate::generators::{Config, DiffValue, DiffValueType};
use crate::oracles::{diff_wasmi::WasmiEngine, diff_wasmtime::WasmtimeEngine};
use anyhow::Error;
use arbitrary::Unstructured;
use wasmtime::Trap;
/// Pick one of the engines implemented in this module that is:
/// - in the list of `allowed` engines
/// - can evaluate Wasm modules compatible with `existing_config`.
pub fn choose(
/// Returns a function which can be used to build the engine name specified.
///
/// `None` is returned if the named engine does not have support compiled into
/// this crate.
pub fn build(
u: &mut Unstructured<'_>,
existing_config: &Config,
allowed: &[&str],
name: &str,
config: &mut Config,
) -> arbitrary::Result<Option<Box<dyn DiffEngine>>> {
// Filter out any engines that cannot match the `existing_config` or are not
// `allowed`.
let mut engines: Vec<Box<dyn DiffEngine>> = vec![];
let engine: Box<dyn DiffEngine> = match name {
"wasmtime" => Box::new(WasmtimeEngine::new(u, config)?),
"wasmi" => Box::new(WasmiEngine::new(config)),
if allowed.contains(&"wasmtime") {
let mut new_wasmtime_config: WasmtimeConfig = u.arbitrary()?;
new_wasmtime_config.make_compatible_with(&existing_config.wasmtime);
let new_config = Config {
wasmtime: new_wasmtime_config,
module_config: existing_config.module_config.clone(),
};
if let Result::Ok(e) = WasmtimeEngine::new(new_config) {
engines.push(Box::new(e))
}
}
#[cfg(feature = "fuzz-spec-interpreter")]
"spec" => Box::new(crate::oracles::diff_spec::SpecInterpreter::new(config)),
#[cfg(not(feature = "fuzz-spec-interpreter"))]
"spec" => return Ok(None),
if allowed.contains(&"wasmi") {
if let Result::Ok(e) = WasmiEngine::new(&existing_config.module_config) {
engines.push(Box::new(e))
}
}
#[cfg(not(any(windows, target_arch = "s390x")))]
"v8" => Box::new(crate::oracles::diff_v8::V8Engine::new(config)),
#[cfg(any(windows, target_arch = "s390x"))]
"v8" => return Ok(None),
#[cfg(feature = "fuzz-spec-interpreter")]
if allowed.contains(&"spec") {
if let Result::Ok(e) =
crate::oracles::diff_spec::SpecInterpreter::new(&existing_config.module_config)
{
engines.push(Box::new(e))
}
}
_ => panic!("unknown engine {name}"),
};
#[cfg(not(any(windows, target_arch = "s390x")))]
if allowed.contains(&"v8") {
if let Result::Ok(e) =
crate::oracles::diff_v8::V8Engine::new(&existing_config.module_config)
{
engines.push(Box::new(e))
}
}
if engines.is_empty() {
return Ok(None);
}
// Use the input of the fuzzer to pick an engine that we'll be fuzzing
// Wasmtime against.
let index: usize = u.int_in_range(0..=engines.len() - 1)?;
let engine = engines.swap_remove(index);
log::debug!("selected engine: {}", engine.name());
Ok(Some(engine))
}
@@ -187,11 +156,11 @@ pub fn parse_env_list(env_variable: &str) -> Option<Vec<String>> {
}
#[cfg(test)]
pub fn smoke_test_engine<T>(mk_engine: impl Fn(Config) -> anyhow::Result<T>)
where
pub fn smoke_test_engine<T>(
mk_engine: impl Fn(&mut arbitrary::Unstructured<'_>, &mut Config) -> arbitrary::Result<T>,
) where
T: DiffEngine,
{
use arbitrary::Arbitrary;
use rand::prelude::*;
let mut rng = SmallRng::seed_from_u64(0);
@@ -199,8 +168,8 @@ where
let n = 100;
for _ in 0..n {
rng.fill_bytes(&mut buf);
let u = Unstructured::new(&buf);
let mut config = match Config::arbitrary_take_rest(u) {
let mut u = Unstructured::new(&buf);
let mut config = match u.arbitrary::<Config>() {
Ok(config) => config,
Err(_) => continue,
};
@@ -208,19 +177,7 @@ where
// settings, can guaranteed instantiate a module.
config.set_differential_config();
// Configure settings to ensure that any filters in engine constructors
// try not to filter out this `Config`.
config.module_config.config.reference_types_enabled = false;
config.module_config.config.bulk_memory_enabled = false;
config.module_config.config.memory64_enabled = false;
config.module_config.config.threads_enabled = false;
config.module_config.config.simd_enabled = false;
config.module_config.config.min_funcs = 1;
config.module_config.config.max_funcs = 1;
config.module_config.config.min_tables = 0;
config.module_config.config.max_tables = 0;
let mut engine = match mk_engine(config) {
let mut engine = match mk_engine(&mut u, &mut config) {
Ok(engine) => engine,
Err(e) => {
println!("skip {:?}", e);