1 //! Generate a configuration for both Wasmtime and the Wasm module to execute. 2 3 use super::{ 4 AsyncConfig, CodegenSettings, InstanceAllocationStrategy, MemoryConfig, ModuleConfig, 5 NormalMemoryConfig, UnalignedMemoryCreator, 6 }; 7 use crate::oracles::{StoreLimits, Timeout}; 8 use anyhow::Result; 9 use arbitrary::{Arbitrary, Unstructured}; 10 use std::sync::Arc; 11 use std::time::Duration; 12 use wasmtime::{Engine, Module, MpkEnabled, Store}; 13 use wasmtime_test_util::wast::{WastConfig, WastTest, limits}; 14 15 /// Configuration for `wasmtime::Config` and generated modules for a session of 16 /// fuzzing. 17 /// 18 /// This configuration guides what modules are generated, how wasmtime 19 /// configuration is generated, and is typically itself generated through a call 20 /// to `Arbitrary` which allows for a form of "swarm testing". 21 #[derive(Debug, Clone)] 22 pub struct Config { 23 /// Configuration related to the `wasmtime::Config`. 24 pub wasmtime: WasmtimeConfig, 25 /// Configuration related to generated modules. 26 pub module_config: ModuleConfig, 27 } 28 29 impl Config { 30 /// Indicates that this configuration is being used for differential 31 /// execution. 32 /// 33 /// The purpose of this function is to update the configuration which was 34 /// generated to be compatible with execution in multiple engines. The goal 35 /// is to produce the exact same result in all engines so we need to paper 36 /// over things like nan differences and memory/table behavior differences. 37 pub fn set_differential_config(&mut self) { 38 let config = &mut self.module_config.config; 39 40 // Make it more likely that there are types available to generate a 41 // function with. 42 config.min_types = config.min_types.max(1); 43 config.max_types = config.max_types.max(1); 44 45 // Generate at least one function 46 config.min_funcs = config.min_funcs.max(1); 47 config.max_funcs = config.max_funcs.max(1); 48 49 // Allow a memory to be generated, but don't let it get too large. 50 // Additionally require the maximum size to guarantee that the growth 51 // behavior is consistent across engines. 52 config.max_memory32_bytes = 10 << 16; 53 config.max_memory64_bytes = 10 << 16; 54 config.memory_max_size_required = true; 55 56 // If tables are generated make sure they don't get too large to avoid 57 // hitting any engine-specific limit. Additionally ensure that the 58 // maximum size is required to guarantee consistent growth across 59 // engines. 60 // 61 // Note that while reference types are disabled below, only allow one 62 // table. 63 config.max_table_elements = 1_000; 64 config.table_max_size_required = true; 65 66 // Don't allow any imports 67 config.max_imports = 0; 68 69 // Try to get the function and the memory exported 70 config.export_everything = true; 71 72 // NaN is canonicalized at the wasm level for differential fuzzing so we 73 // can paper over NaN differences between engines. 74 config.canonicalize_nans = true; 75 76 // If using the pooling allocator, update the instance limits too 77 if let InstanceAllocationStrategy::Pooling(pooling) = &mut self.wasmtime.strategy { 78 // One single-page memory 79 pooling.total_memories = config.max_memories as u32; 80 pooling.max_memory_size = 10 << 16; 81 pooling.max_memories_per_module = config.max_memories as u32; 82 if pooling.memory_protection_keys == MpkEnabled::Auto 83 && pooling.max_memory_protection_keys > 1 84 { 85 pooling.total_memories = 86 pooling.total_memories * (pooling.max_memory_protection_keys as u32); 87 } 88 89 pooling.total_tables = config.max_tables as u32; 90 pooling.table_elements = 1_000; 91 pooling.max_tables_per_module = config.max_tables as u32; 92 93 pooling.core_instance_size = 1_000_000; 94 95 if let MemoryConfig::Normal(cfg) = &mut self.wasmtime.memory_config { 96 match &mut cfg.memory_reservation { 97 Some(size) => *size = (*size).max(pooling.max_memory_size as u64), 98 other @ None => *other = Some(pooling.max_memory_size as u64), 99 } 100 } 101 } 102 103 // These instructions are explicitly not expected to be exactly the same 104 // across engines. Don't fuzz them. 105 config.relaxed_simd_enabled = false; 106 } 107 108 /// Uses this configuration and the supplied source of data to generate 109 /// a wasm module. 110 /// 111 /// If a `default_fuel` is provided, the resulting module will be configured 112 /// to ensure termination; as doing so will add an additional global to the module, 113 /// the pooling allocator, if configured, will also have its globals limit updated. 114 pub fn generate( 115 &self, 116 input: &mut Unstructured<'_>, 117 default_fuel: Option<u32>, 118 ) -> arbitrary::Result<wasm_smith::Module> { 119 self.module_config.generate(input, default_fuel) 120 } 121 122 /// Updates this configuration to be able to run the `test` specified. 123 /// 124 /// This primarily updates `self.module_config` to ensure that it enables 125 /// all features and proposals necessary to execute the `test` specified. 126 /// This will additionally update limits in the pooling allocator to be able 127 /// to execute all tests. 128 pub fn make_wast_test_compliant(&mut self, test: &WastTest) -> WastConfig { 129 let wasmtime_test_util::wast::TestConfig { 130 memory64, 131 custom_page_sizes, 132 multi_memory, 133 threads, 134 shared_everything_threads, 135 gc, 136 function_references, 137 relaxed_simd, 138 reference_types, 139 tail_call, 140 extended_const, 141 wide_arithmetic, 142 component_model_async, 143 component_model_async_builtins, 144 component_model_async_stackful, 145 component_model_error_context, 146 simd, 147 exceptions, 148 legacy_exceptions, 149 150 hogs_memory: _, 151 nan_canonicalization: _, 152 gc_types: _, 153 stack_switching: _, 154 spec_test: _, 155 } = test.config; 156 157 // Enable/disable some proposals that aren't configurable in wasm-smith 158 // but are configurable in Wasmtime. 159 self.module_config.function_references_enabled = 160 function_references.or(gc).unwrap_or(false); 161 self.module_config.component_model_async = component_model_async.unwrap_or(false); 162 self.module_config.component_model_async_builtins = 163 component_model_async_builtins.unwrap_or(false); 164 self.module_config.component_model_async_stackful = 165 component_model_async_stackful.unwrap_or(false); 166 self.module_config.component_model_error_context = 167 component_model_error_context.unwrap_or(false); 168 self.module_config.legacy_exceptions = legacy_exceptions.unwrap_or(false); 169 170 // Enable/disable proposals that wasm-smith has knobs for which will be 171 // read when creating `wasmtime::Config`. 172 let config = &mut self.module_config.config; 173 config.bulk_memory_enabled = true; 174 config.multi_value_enabled = true; 175 config.wide_arithmetic_enabled = wide_arithmetic.unwrap_or(false); 176 config.memory64_enabled = memory64.unwrap_or(false); 177 config.relaxed_simd_enabled = relaxed_simd.unwrap_or(false); 178 config.simd_enabled = config.relaxed_simd_enabled || simd.unwrap_or(false); 179 config.tail_call_enabled = tail_call.unwrap_or(false); 180 config.custom_page_sizes_enabled = custom_page_sizes.unwrap_or(false); 181 config.threads_enabled = threads.unwrap_or(false); 182 config.shared_everything_threads_enabled = shared_everything_threads.unwrap_or(false); 183 config.gc_enabled = gc.unwrap_or(false); 184 config.reference_types_enabled = config.gc_enabled 185 || self.module_config.function_references_enabled 186 || reference_types.unwrap_or(false); 187 config.extended_const_enabled = extended_const.unwrap_or(false); 188 config.exceptions_enabled = exceptions.unwrap_or(false); 189 if multi_memory.unwrap_or(false) { 190 config.max_memories = limits::MEMORIES_PER_MODULE as usize; 191 } else { 192 config.max_memories = 1; 193 } 194 195 match &mut self.wasmtime.memory_config { 196 MemoryConfig::Normal(config) => { 197 if let Some(n) = &mut config.memory_reservation { 198 *n = (*n).max(limits::MEMORY_SIZE as u64); 199 } 200 } 201 MemoryConfig::CustomUnaligned => {} 202 } 203 204 // FIXME: it might be more ideal to avoid the need for this entirely 205 // and to just let the test fail. If a test fails due to a pooling 206 // allocator resource limit being met we could ideally detect that and 207 // let the fuzz test case pass. That would avoid the need to hardcode 208 // so much here and in theory wouldn't reduce the usefulness of fuzzers 209 // all that much. At this time though we can't easily test this configuration. 210 if let InstanceAllocationStrategy::Pooling(pooling) = &mut self.wasmtime.strategy { 211 // Clamp protection keys between 1 & 2 to reduce the number of 212 // slots and then multiply the total memories by the number of keys 213 // we have since a single store has access to only one key. 214 pooling.max_memory_protection_keys = pooling.max_memory_protection_keys.max(1).min(2); 215 pooling.total_memories = pooling 216 .total_memories 217 .max(limits::MEMORIES * (pooling.max_memory_protection_keys as u32)); 218 219 // For other limits make sure they meet the minimum threshold 220 // required for our wast tests. 221 pooling.total_component_instances = pooling 222 .total_component_instances 223 .max(limits::COMPONENT_INSTANCES); 224 pooling.total_tables = pooling.total_tables.max(limits::TABLES); 225 pooling.max_tables_per_module = 226 pooling.max_tables_per_module.max(limits::TABLES_PER_MODULE); 227 pooling.max_memories_per_module = pooling 228 .max_memories_per_module 229 .max(limits::MEMORIES_PER_MODULE); 230 pooling.max_memories_per_component = pooling 231 .max_memories_per_component 232 .max(limits::MEMORIES_PER_MODULE); 233 pooling.total_core_instances = pooling.total_core_instances.max(limits::CORE_INSTANCES); 234 pooling.max_memory_size = pooling.max_memory_size.max(limits::MEMORY_SIZE); 235 pooling.table_elements = pooling.table_elements.max(limits::TABLE_ELEMENTS); 236 pooling.core_instance_size = pooling.core_instance_size.max(limits::CORE_INSTANCE_SIZE); 237 pooling.component_instance_size = pooling 238 .component_instance_size 239 .max(limits::CORE_INSTANCE_SIZE); 240 } 241 242 // Return the test configuration that this fuzz configuration represents 243 // which is used afterwards to test if the `test` here is expected to 244 // fail or not. 245 WastConfig { 246 collector: match self.wasmtime.collector { 247 Collector::Null => wasmtime_test_util::wast::Collector::Null, 248 Collector::DeferredReferenceCounting => { 249 wasmtime_test_util::wast::Collector::DeferredReferenceCounting 250 } 251 }, 252 pooling: matches!( 253 self.wasmtime.strategy, 254 InstanceAllocationStrategy::Pooling(_) 255 ), 256 compiler: match self.wasmtime.compiler_strategy { 257 CompilerStrategy::CraneliftNative => { 258 wasmtime_test_util::wast::Compiler::CraneliftNative 259 } 260 CompilerStrategy::CraneliftPulley => { 261 wasmtime_test_util::wast::Compiler::CraneliftPulley 262 } 263 CompilerStrategy::Winch => wasmtime_test_util::wast::Compiler::Winch, 264 }, 265 } 266 } 267 268 /// Converts this to a `wasmtime::Config` object 269 pub fn to_wasmtime(&self) -> wasmtime::Config { 270 crate::init_fuzzing(); 271 272 let mut cfg = wasmtime_cli_flags::CommonOptions::default(); 273 cfg.codegen.native_unwind_info = 274 Some(cfg!(target_os = "windows") || self.wasmtime.native_unwind_info); 275 cfg.codegen.parallel_compilation = Some(false); 276 cfg.debug.address_map = Some(self.wasmtime.generate_address_map); 277 cfg.opts.opt_level = Some(self.wasmtime.opt_level.to_wasmtime()); 278 cfg.opts.regalloc_algorithm = Some(self.wasmtime.regalloc_algorithm.to_wasmtime()); 279 cfg.opts.signals_based_traps = Some(self.wasmtime.signals_based_traps); 280 cfg.opts.memory_guaranteed_dense_image_size = Some(std::cmp::min( 281 // Clamp this at 16MiB so we don't get huge in-memory 282 // images during fuzzing. 283 16 << 20, 284 self.wasmtime.memory_guaranteed_dense_image_size, 285 )); 286 cfg.wasm.async_stack_zeroing = Some(self.wasmtime.async_stack_zeroing); 287 cfg.wasm.bulk_memory = Some(true); 288 cfg.wasm.component_model_async = Some(self.module_config.component_model_async); 289 cfg.wasm.component_model_async_builtins = 290 Some(self.module_config.component_model_async_builtins); 291 cfg.wasm.component_model_async_stackful = 292 Some(self.module_config.component_model_async_stackful); 293 cfg.wasm.component_model_error_context = 294 Some(self.module_config.component_model_error_context); 295 cfg.wasm.custom_page_sizes = Some(self.module_config.config.custom_page_sizes_enabled); 296 cfg.wasm.epoch_interruption = Some(self.wasmtime.epoch_interruption); 297 cfg.wasm.extended_const = Some(self.module_config.config.extended_const_enabled); 298 cfg.wasm.fuel = self.wasmtime.consume_fuel.then(|| u64::MAX); 299 cfg.wasm.function_references = Some(self.module_config.function_references_enabled); 300 cfg.wasm.gc = Some(self.module_config.config.gc_enabled); 301 cfg.wasm.memory64 = Some(self.module_config.config.memory64_enabled); 302 cfg.wasm.multi_memory = Some(self.module_config.config.max_memories > 1); 303 cfg.wasm.multi_value = Some(self.module_config.config.multi_value_enabled); 304 cfg.wasm.nan_canonicalization = Some(self.wasmtime.canonicalize_nans); 305 cfg.wasm.reference_types = Some(self.module_config.config.reference_types_enabled); 306 cfg.wasm.simd = Some(self.module_config.config.simd_enabled); 307 cfg.wasm.tail_call = Some(self.module_config.config.tail_call_enabled); 308 cfg.wasm.threads = Some(self.module_config.config.threads_enabled); 309 cfg.wasm.shared_everything_threads = 310 Some(self.module_config.config.shared_everything_threads_enabled); 311 cfg.wasm.wide_arithmetic = Some(self.module_config.config.wide_arithmetic_enabled); 312 cfg.wasm.exceptions = Some(self.module_config.config.exceptions_enabled); 313 cfg.wasm.legacy_exceptions = Some(self.module_config.legacy_exceptions); 314 if !self.module_config.config.simd_enabled { 315 cfg.wasm.relaxed_simd = Some(false); 316 } 317 cfg.codegen.collector = Some(self.wasmtime.collector.to_wasmtime()); 318 319 let compiler_strategy = &self.wasmtime.compiler_strategy; 320 let cranelift_strategy = match compiler_strategy { 321 CompilerStrategy::CraneliftNative | CompilerStrategy::CraneliftPulley => true, 322 CompilerStrategy::Winch => false, 323 }; 324 self.wasmtime.compiler_strategy.configure(&mut cfg); 325 326 self.wasmtime.codegen.configure(&mut cfg); 327 328 // Determine whether we will actually enable PCC -- this is 329 // disabled if the module requires memory64, which is not yet 330 // compatible (due to the need for dynamic checks). 331 let pcc = cfg!(feature = "fuzz-pcc") 332 && self.wasmtime.pcc 333 && !self.module_config.config.memory64_enabled; 334 335 // Only set cranelift specific flags when the Cranelift strategy is 336 // chosen. 337 if cranelift_strategy { 338 // If the wasm-smith-generated module use nan canonicalization then we 339 // don't need to enable it, but if it doesn't enable it already then we 340 // enable this codegen option. 341 cfg.wasm.nan_canonicalization = Some(!self.module_config.config.canonicalize_nans); 342 343 // Enabling the verifier will at-least-double compilation time, which 344 // with a 20-30x slowdown in fuzzing can cause issues related to 345 // timeouts. If generated modules can have more than a small handful of 346 // functions then disable the verifier when fuzzing to try to lessen the 347 // impact of timeouts. 348 if self.module_config.config.max_funcs > 10 { 349 cfg.codegen.cranelift_debug_verifier = Some(false); 350 } 351 352 if self.wasmtime.force_jump_veneers { 353 cfg.codegen.cranelift.push(( 354 "wasmtime_linkopt_force_jump_veneer".to_string(), 355 Some("true".to_string()), 356 )); 357 } 358 359 if let Some(pad) = self.wasmtime.padding_between_functions { 360 cfg.codegen.cranelift.push(( 361 "wasmtime_linkopt_padding_between_functions".to_string(), 362 Some(pad.to_string()), 363 )); 364 } 365 366 cfg.codegen.pcc = Some(pcc); 367 368 // Eager init is currently only supported on Cranelift, not Winch. 369 cfg.opts.table_lazy_init = Some(self.wasmtime.table_lazy_init); 370 } 371 372 self.wasmtime.strategy.configure(&mut cfg); 373 374 // Vary the memory configuration, but only if threads are not enabled. 375 // When the threads proposal is enabled we might generate shared memory, 376 // which is less amenable to different memory configurations: 377 // - shared memories are required to be "static" so fuzzing the various 378 // memory configurations will mostly result in uninteresting errors. 379 // The interesting part about shared memories is the runtime so we 380 // don't fuzz non-default settings. 381 // - shared memories are required to be aligned which means that the 382 // `CustomUnaligned` variant isn't actually safe to use with a shared 383 // memory. 384 let host_memory = if !self.module_config.config.threads_enabled { 385 // If PCC is enabled, force other options to be compatible: PCC is currently only 386 // supported when bounds checks are elided. 387 let memory_config = if pcc { 388 MemoryConfig::Normal(NormalMemoryConfig { 389 memory_reservation: Some(4 << 30), // 4 GiB 390 memory_guard_size: Some(2 << 30), // 2 GiB 391 memory_reservation_for_growth: Some(0), 392 guard_before_linear_memory: false, 393 memory_init_cow: true, 394 // Doesn't matter, only using virtual memory. 395 cranelift_enable_heap_access_spectre_mitigations: None, 396 }) 397 } else { 398 self.wasmtime.memory_config.clone() 399 }; 400 401 match &memory_config { 402 MemoryConfig::Normal(memory_config) => { 403 memory_config.configure(&mut cfg); 404 None 405 } 406 MemoryConfig::CustomUnaligned => { 407 cfg.opts.memory_reservation = Some(0); 408 cfg.opts.memory_guard_size = Some(0); 409 cfg.opts.memory_reservation_for_growth = Some(0); 410 cfg.opts.guard_before_linear_memory = Some(false); 411 cfg.opts.memory_init_cow = Some(false); 412 log::debug!("a custom unaligned host memory will be in use"); 413 Some(Arc::new(UnalignedMemoryCreator)) 414 } 415 } 416 } else { 417 None 418 }; 419 420 // If malloc-based memory is going to be used, which requires these four 421 // options set to specific values (and Pulley auto-sets two of them) 422 // then be sure to cap `memory_reservation_for_growth` at a smaller 423 // value than the default. For malloc-based memory reservation beyond 424 // the end of memory isn't captured by `StoreLimiter` so we need to be 425 // sure it's small enough to not blow OOM limits while fuzzing. 426 if ((cfg.opts.signals_based_traps == Some(true) && cfg.opts.memory_guard_size == Some(0)) 427 || self.wasmtime.compiler_strategy == CompilerStrategy::CraneliftPulley) 428 && cfg.opts.memory_reservation == Some(0) 429 && cfg.opts.memory_init_cow == Some(false) 430 { 431 let growth = &mut cfg.opts.memory_reservation_for_growth; 432 let max = 1 << 20; 433 *growth = match *growth { 434 Some(n) => Some(n.min(max)), 435 None => Some(max), 436 }; 437 } 438 439 log::debug!("creating wasmtime config with CLI options:\n{cfg}"); 440 let mut cfg = cfg.config(None).expect("failed to create wasmtime::Config"); 441 442 if let Some(host_memory) = host_memory { 443 cfg.with_host_memory(host_memory); 444 } 445 446 if self.wasmtime.async_config != AsyncConfig::Disabled { 447 log::debug!("async config in use {:?}", self.wasmtime.async_config); 448 self.wasmtime.async_config.configure(&mut cfg); 449 } 450 451 return cfg; 452 } 453 454 /// Convenience function for generating a `Store<T>` using this 455 /// configuration. 456 pub fn to_store(&self) -> Store<StoreLimits> { 457 let engine = Engine::new(&self.to_wasmtime()).unwrap(); 458 let mut store = Store::new(&engine, StoreLimits::new()); 459 self.configure_store(&mut store); 460 store 461 } 462 463 /// Configures a store based on this configuration. 464 pub fn configure_store(&self, store: &mut Store<StoreLimits>) { 465 store.limiter(|s| s as &mut dyn wasmtime::ResourceLimiter); 466 467 // Configure the store to never abort by default, that is it'll have 468 // max fuel or otherwise trap on an epoch change but the epoch won't 469 // ever change. 470 // 471 // Afterwards though see what `AsyncConfig` is being used an further 472 // refine the store's configuration based on that. 473 if self.wasmtime.consume_fuel { 474 store.set_fuel(u64::MAX).unwrap(); 475 } 476 if self.wasmtime.epoch_interruption { 477 store.epoch_deadline_trap(); 478 store.set_epoch_deadline(1); 479 } 480 match self.wasmtime.async_config { 481 AsyncConfig::Disabled => {} 482 AsyncConfig::YieldWithFuel(amt) => { 483 assert!(self.wasmtime.consume_fuel); 484 store.fuel_async_yield_interval(Some(amt)).unwrap(); 485 } 486 AsyncConfig::YieldWithEpochs { ticks, .. } => { 487 assert!(self.wasmtime.epoch_interruption); 488 store.set_epoch_deadline(ticks); 489 store.epoch_deadline_async_yield_and_update(ticks); 490 } 491 } 492 } 493 494 /// Generates an arbitrary method of timing out an instance, ensuring that 495 /// this configuration supports the returned timeout. 496 pub fn generate_timeout(&mut self, u: &mut Unstructured<'_>) -> arbitrary::Result<Timeout> { 497 let time_duration = Duration::from_millis(100); 498 let timeout = u 499 .choose(&[Timeout::Fuel(100_000), Timeout::Epoch(time_duration)])? 500 .clone(); 501 match &timeout { 502 Timeout::Fuel(..) => { 503 self.wasmtime.consume_fuel = true; 504 } 505 Timeout::Epoch(..) => { 506 self.wasmtime.epoch_interruption = true; 507 } 508 Timeout::None => unreachable!("Not an option given to choose()"), 509 } 510 Ok(timeout) 511 } 512 513 /// Compiles the `wasm` within the `engine` provided. 514 /// 515 /// This notably will use `Module::{serialize,deserialize_file}` to 516 /// round-trip if configured in the fuzzer. 517 pub fn compile(&self, engine: &Engine, wasm: &[u8]) -> Result<Module> { 518 // Propagate this error in case the caller wants to handle 519 // valid-vs-invalid wasm. 520 let module = Module::new(engine, wasm)?; 521 if !self.wasmtime.use_precompiled_cwasm { 522 return Ok(module); 523 } 524 525 // Don't propagate these errors to prevent them from accidentally being 526 // interpreted as invalid wasm, these should never fail on a 527 // well-behaved host system. 528 let dir = tempfile::TempDir::new().unwrap(); 529 let file = dir.path().join("module.wasm"); 530 std::fs::write(&file, module.serialize().unwrap()).unwrap(); 531 unsafe { Ok(Module::deserialize_file(engine, &file).unwrap()) } 532 } 533 534 /// Updates this configuration to forcibly enable async support. Only useful 535 /// in fuzzers which do async calls. 536 pub fn enable_async(&mut self, u: &mut Unstructured<'_>) -> arbitrary::Result<()> { 537 if self.wasmtime.consume_fuel || u.arbitrary()? { 538 self.wasmtime.async_config = 539 AsyncConfig::YieldWithFuel(u.int_in_range(1000..=100_000)?); 540 self.wasmtime.consume_fuel = true; 541 } else { 542 self.wasmtime.async_config = AsyncConfig::YieldWithEpochs { 543 dur: Duration::from_millis(u.int_in_range(1..=10)?), 544 ticks: u.int_in_range(1..=10)?, 545 }; 546 self.wasmtime.epoch_interruption = true; 547 } 548 Ok(()) 549 } 550 } 551 552 impl<'a> Arbitrary<'a> for Config { 553 fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> { 554 let mut config = Self { 555 wasmtime: u.arbitrary()?, 556 module_config: u.arbitrary()?, 557 }; 558 559 config 560 .wasmtime 561 .update_module_config(&mut config.module_config, u)?; 562 563 Ok(config) 564 } 565 } 566 567 /// Configuration related to `wasmtime::Config` and the various settings which 568 /// can be tweaked from within. 569 #[derive(Arbitrary, Clone, Debug, Eq, Hash, PartialEq)] 570 pub struct WasmtimeConfig { 571 opt_level: OptLevel, 572 regalloc_algorithm: RegallocAlgorithm, 573 debug_info: bool, 574 canonicalize_nans: bool, 575 interruptable: bool, 576 pub(crate) consume_fuel: bool, 577 pub(crate) epoch_interruption: bool, 578 /// The Wasmtime memory configuration to use. 579 pub memory_config: MemoryConfig, 580 force_jump_veneers: bool, 581 memory_init_cow: bool, 582 memory_guaranteed_dense_image_size: u64, 583 use_precompiled_cwasm: bool, 584 async_stack_zeroing: bool, 585 /// Configuration for the instance allocation strategy to use. 586 pub strategy: InstanceAllocationStrategy, 587 codegen: CodegenSettings, 588 padding_between_functions: Option<u16>, 589 generate_address_map: bool, 590 native_unwind_info: bool, 591 /// Configuration for the compiler to use. 592 pub compiler_strategy: CompilerStrategy, 593 collector: Collector, 594 table_lazy_init: bool, 595 596 /// Whether or not fuzzing should enable PCC. 597 pcc: bool, 598 599 /// Configuration for whether wasm is invoked in an async fashion and how 600 /// it's cooperatively time-sliced. 601 pub async_config: AsyncConfig, 602 603 /// Whether or not host signal handlers are enabled for this configuration, 604 /// aka whether signal handlers are supported. 605 signals_based_traps: bool, 606 } 607 608 impl WasmtimeConfig { 609 /// Force `self` to be a configuration compatible with `other`. This is 610 /// useful for differential execution to avoid unhelpful fuzz crashes when 611 /// one engine has a feature enabled and the other does not. 612 pub fn make_compatible_with(&mut self, other: &Self) { 613 // Use the same allocation strategy between the two configs. 614 // 615 // Ideally this wouldn't be necessary, but, during differential 616 // evaluation, if the `lhs` is using ondemand and the `rhs` is using the 617 // pooling allocator (or vice versa), then the module may have been 618 // generated in such a way that is incompatible with the other 619 // allocation strategy. 620 // 621 // We can remove this in the future when it's possible to access the 622 // fields of `wasm_smith::Module` to constrain the pooling allocator 623 // based on what was actually generated. 624 self.strategy = other.strategy.clone(); 625 if let InstanceAllocationStrategy::Pooling { .. } = &other.strategy { 626 // Also use the same memory configuration when using the pooling 627 // allocator. 628 self.memory_config = other.memory_config.clone(); 629 } 630 631 self.make_internally_consistent(); 632 } 633 634 /// Updates `config` to be compatible with `self` and the other way around 635 /// too. 636 pub fn update_module_config( 637 &mut self, 638 config: &mut ModuleConfig, 639 u: &mut Unstructured<'_>, 640 ) -> arbitrary::Result<()> { 641 match self.compiler_strategy { 642 CompilerStrategy::CraneliftNative => {} 643 644 CompilerStrategy::Winch => { 645 // Winch is not complete on non-x64 targets, so just abandon this test 646 // case. We don't want to force Cranelift because we change what module 647 // config features are enabled based on the compiler strategy, and we 648 // don't want to make the same fuzz input DNA generate different test 649 // cases on different targets. 650 if cfg!(not(target_arch = "x86_64")) { 651 log::warn!( 652 "want to compile with Winch but host architecture does not support it" 653 ); 654 return Err(arbitrary::Error::IncorrectFormat); 655 } 656 657 // Winch doesn't support the same set of wasm proposal as Cranelift 658 // at this time, so if winch is selected be sure to disable wasm 659 // proposals in `Config` to ensure that Winch can compile the 660 // module that wasm-smith generates. 661 config.config.relaxed_simd_enabled = false; 662 config.config.gc_enabled = false; 663 config.config.tail_call_enabled = false; 664 config.config.reference_types_enabled = false; 665 config.function_references_enabled = false; 666 667 // Winch's SIMD implementations require AVX and AVX2. 668 if self 669 .codegen_flag("has_avx") 670 .is_some_and(|value| value == "false") 671 || self 672 .codegen_flag("has_avx2") 673 .is_some_and(|value| value == "false") 674 { 675 config.config.simd_enabled = false; 676 } 677 678 // Tuning the following engine options is currently not supported 679 // by Winch. 680 self.signals_based_traps = true; 681 self.table_lazy_init = true; 682 self.debug_info = false; 683 } 684 685 CompilerStrategy::CraneliftPulley => { 686 config.config.threads_enabled = false; 687 } 688 } 689 690 // Forcibly don't use the `CustomUnaligned` memory configuration when 691 // wasm threads are enabled or when the pooling allocator is used. For 692 // the pooling allocator it doesn't use custom memory creators anyway 693 // and for wasm threads that will require some refactoring of the 694 // `LinearMemory` trait to bubble up the request that the linear memory 695 // not move. Otherwise that just generates a panic right now. 696 if config.config.threads_enabled 697 || matches!(self.strategy, InstanceAllocationStrategy::Pooling(_)) 698 { 699 self.avoid_custom_unaligned_memory(u)?; 700 } 701 702 // If using the pooling allocator, constrain the memory and module configurations 703 // to the module limits. 704 if let InstanceAllocationStrategy::Pooling(pooling) = &mut self.strategy { 705 // If the pooling allocator is used, do not allow shared memory to 706 // be created. FIXME: see 707 // https://github.com/bytecodealliance/wasmtime/issues/4244. 708 config.config.threads_enabled = false; 709 710 // Ensure the pooling allocator can support the maximal size of 711 // memory, picking the smaller of the two to win. 712 let min_bytes = config 713 .config 714 .max_memory32_bytes 715 // memory64_bytes is a u128, but since we are taking the min 716 // we can truncate it down to a u64. 717 .min( 718 config 719 .config 720 .max_memory64_bytes 721 .try_into() 722 .unwrap_or(u64::MAX), 723 ); 724 let mut min = min_bytes.min(pooling.max_memory_size as u64); 725 if let MemoryConfig::Normal(cfg) = &self.memory_config { 726 min = min.min(cfg.memory_reservation.unwrap_or(0)); 727 } 728 pooling.max_memory_size = min as usize; 729 config.config.max_memory32_bytes = min; 730 config.config.max_memory64_bytes = min as u128; 731 732 // If traps are disallowed then memories must have at least one page 733 // of memory so if we still are only allowing 0 pages of memory then 734 // increase that to one here. 735 if config.config.disallow_traps { 736 if pooling.max_memory_size < (1 << 16) { 737 pooling.max_memory_size = 1 << 16; 738 config.config.max_memory32_bytes = 1 << 16; 739 config.config.max_memory64_bytes = 1 << 16; 740 if let MemoryConfig::Normal(cfg) = &mut self.memory_config { 741 match &mut cfg.memory_reservation { 742 Some(size) => *size = (*size).max(pooling.max_memory_size as u64), 743 size @ None => *size = Some(pooling.max_memory_size as u64), 744 } 745 } 746 } 747 // .. additionally update tables 748 if pooling.table_elements == 0 { 749 pooling.table_elements = 1; 750 } 751 } 752 753 // Don't allow too many linear memories per instance since massive 754 // virtual mappings can fail to get allocated. 755 config.config.min_memories = config.config.min_memories.min(10); 756 config.config.max_memories = config.config.max_memories.min(10); 757 758 // Force this pooling allocator to always be able to accommodate the 759 // module that may be generated. 760 pooling.total_memories = config.config.max_memories as u32; 761 pooling.total_tables = config.config.max_tables as u32; 762 } 763 764 if !self.signals_based_traps { 765 // At this time shared memories require a "static" memory 766 // configuration but when signals-based traps are disabled all 767 // memories are forced to the "dynamic" configuration. This is 768 // fixable with some more work on the bounds-checks side of things 769 // to do a full bounds check even on static memories, but that's 770 // left for a future PR. 771 config.config.threads_enabled = false; 772 773 // Spectre-based heap mitigations require signal handlers so this 774 // must always be disabled if signals-based traps are disabled. 775 if let MemoryConfig::Normal(cfg) = &mut self.memory_config { 776 cfg.cranelift_enable_heap_access_spectre_mitigations = None; 777 } 778 } 779 780 self.make_internally_consistent(); 781 782 Ok(()) 783 } 784 785 /// Returns the codegen flag value, if any, for `name`. 786 pub(crate) fn codegen_flag(&self, name: &str) -> Option<&str> { 787 self.codegen.flags().iter().find_map(|(n, value)| { 788 if n == name { 789 Some(value.as_str()) 790 } else { 791 None 792 } 793 }) 794 } 795 796 /// Helper to switch `MemoryConfig::CustomUnaligned` to 797 /// `MemoryConfig::Normal` 798 fn avoid_custom_unaligned_memory(&mut self, u: &mut Unstructured<'_>) -> arbitrary::Result<()> { 799 if let MemoryConfig::CustomUnaligned = self.memory_config { 800 self.memory_config = MemoryConfig::Normal(u.arbitrary()?); 801 } 802 Ok(()) 803 } 804 805 /// Helper method to handle some dependencies between various configuration 806 /// options. This is intended to be called whenever a `Config` is created or 807 /// modified to ensure that the final result is an instantiable `Config`. 808 /// 809 /// Note that in general this probably shouldn't exist and anything here can 810 /// be considered a "TODO" to go implement more stuff in Wasmtime to accept 811 /// these sorts of configurations. For now though it's intended to reflect 812 /// the current state of the engine's development. 813 fn make_internally_consistent(&mut self) { 814 if !self.signals_based_traps { 815 if let MemoryConfig::Normal(cfg) = &mut self.memory_config { 816 // Spectre-based heap mitigations require signal handlers so 817 // this must always be disabled if signals-based traps are 818 // disabled. 819 cfg.cranelift_enable_heap_access_spectre_mitigations = None; 820 821 // With configuration settings that match the use of malloc for 822 // linear memories cap the `memory_reservation_for_growth` value 823 // to something reasonable to avoid OOM in fuzzing. 824 if !cfg.memory_init_cow 825 && cfg.memory_guard_size == Some(0) 826 && cfg.memory_reservation == Some(0) 827 { 828 let min = 10 << 20; // 10 MiB 829 if let Some(val) = &mut cfg.memory_reservation_for_growth { 830 *val = (*val).min(min); 831 } else { 832 cfg.memory_reservation_for_growth = Some(min); 833 } 834 } 835 } 836 } 837 } 838 } 839 840 #[derive(Arbitrary, Clone, Debug, PartialEq, Eq, Hash)] 841 enum OptLevel { 842 None, 843 Speed, 844 SpeedAndSize, 845 } 846 847 impl OptLevel { 848 fn to_wasmtime(&self) -> wasmtime::OptLevel { 849 match self { 850 OptLevel::None => wasmtime::OptLevel::None, 851 OptLevel::Speed => wasmtime::OptLevel::Speed, 852 OptLevel::SpeedAndSize => wasmtime::OptLevel::SpeedAndSize, 853 } 854 } 855 } 856 857 #[derive(Arbitrary, Clone, Debug, PartialEq, Eq, Hash)] 858 enum RegallocAlgorithm { 859 Backtracking, 860 SinglePass, 861 } 862 863 impl RegallocAlgorithm { 864 fn to_wasmtime(&self) -> wasmtime::RegallocAlgorithm { 865 match self { 866 RegallocAlgorithm::Backtracking => wasmtime::RegallocAlgorithm::Backtracking, 867 // Note: we have disabled `single_pass` for now because of 868 // its limitations w.r.t. exception handling 869 // (https://github.com/bytecodealliance/regalloc2/issues/217). To 870 // avoid breaking all existing fuzzbugs by changing the 871 // `arbitrary` mappings, we keep the `RegallocAlgorithm` 872 // enum as it is and remap here to `Backtracking`. 873 RegallocAlgorithm::SinglePass => wasmtime::RegallocAlgorithm::Backtracking, 874 } 875 } 876 } 877 878 #[derive(Clone, Debug, PartialEq, Eq, Hash)] 879 /// Compiler to use. 880 pub enum CompilerStrategy { 881 /// Cranelift compiler for the native architecture. 882 CraneliftNative, 883 /// Winch compiler. 884 Winch, 885 /// Cranelift compiler for the native architecture. 886 CraneliftPulley, 887 } 888 889 impl CompilerStrategy { 890 /// Configures `config` to use this compilation strategy 891 pub fn configure(&self, config: &mut wasmtime_cli_flags::CommonOptions) { 892 match self { 893 CompilerStrategy::CraneliftNative => { 894 config.codegen.compiler = Some(wasmtime::Strategy::Cranelift); 895 } 896 CompilerStrategy::Winch => { 897 config.codegen.compiler = Some(wasmtime::Strategy::Winch); 898 } 899 CompilerStrategy::CraneliftPulley => { 900 config.codegen.compiler = Some(wasmtime::Strategy::Cranelift); 901 config.target = Some("pulley64".to_string()); 902 } 903 } 904 } 905 } 906 907 impl Arbitrary<'_> for CompilerStrategy { 908 fn arbitrary(u: &mut Unstructured<'_>) -> arbitrary::Result<Self> { 909 // Favor fuzzing native cranelift, but if allowed also enable 910 // winch/pulley. 911 match u.int_in_range(0..=19)? { 912 1 => Ok(Self::CraneliftPulley), 913 2 => Ok(Self::Winch), 914 _ => Ok(Self::CraneliftNative), 915 } 916 } 917 } 918 919 #[derive(Arbitrary, Clone, Debug, PartialEq, Eq, Hash)] 920 pub enum Collector { 921 DeferredReferenceCounting, 922 Null, 923 } 924 925 impl Collector { 926 fn to_wasmtime(&self) -> wasmtime::Collector { 927 match self { 928 Collector::DeferredReferenceCounting => wasmtime::Collector::DeferredReferenceCounting, 929 Collector::Null => wasmtime::Collector::Null, 930 } 931 } 932 } 933