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Add resource limiting to the Wasmtime API. (#2736)

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* Add resource limiting to the Wasmtime API.

This commit adds a `ResourceLimiter` trait to the Wasmtime API.

When used in conjunction with `Store::new_with_limiter`, this can be used to
monitor and prevent WebAssembly code from growing linear memories and tables.

This is particularly useful when hosts need to take into account host resource
usage to determine if WebAssembly code can consume more resources.

A simple `StaticResourceLimiter` is also included with these changes that will
simply limit the size of linear memories or tables for all instances created in
the store based on static values.

* Code review feedback.

* Implemented `StoreLimits` and `StoreLimitsBuilder`.
* Moved `max_instances`, `max_memories`, `max_tables` out of `Config` and into
  `StoreLimits`.
* Moved storage of the limiter in the runtime into `Memory` and `Table`.
* Made `InstanceAllocationRequest` use a reference to the limiter.
* Updated docs.
* Made `ResourceLimiterProxy` generic to remove a level of indirection.
* Fixed the limiter not being used for `wasmtime::Memory` and
  `wasmtime::Table`.

* Code review feedback and bug fix.

* `Memory::new` now returns `Result<Self>` so that an error can be returned if
  the initial requested memory exceeds any limits placed on the store.

* Changed an `Arc` to `Rc` as the `Arc` wasn't necessary.

* Removed `Store` from the `ResourceLimiter` callbacks. Custom resource limiter
  implementations are free to capture any context they want, so no need to
  unnecessarily store a weak reference to `Store` from the proxy type.

* Fixed a bug in the pooling instance allocator where an instance would be
  leaked from the pool. Previously, this would only have happened if the OS was
  unable to make the necessary linear memory available for the instance. With
  these changes, however, the instance might not be created due to limits
  placed on the store. We now properly deallocate the instance on error.

* Added more tests, including one that covers the fix mentioned above.

* Code review feedback.

* Add another memory to `test_pooling_allocator_initial_limits_exceeded` to
  ensure a partially created instance is successfully deallocated.
* Update some doc comments for better documentation of `Store` and
  `ResourceLimiter`.
This commit is contained in:
Peter Huene
2021-04-19 07:19:20 -07:00
committed by GitHub
parent 52b1166918
commit f12b4c467c
30 changed files with 1063 additions and 218 deletions
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103
crates/runtime/src/table.rs
View File

@@ -3,19 +3,21 @@
//! `Table` is to WebAssembly tables what `LinearMemory` is to WebAssembly linear memories.
use crate::vmcontext::{VMCallerCheckedAnyfunc, VMTableDefinition};
use crate::{Trap, VMExternRef};
use crate::{ResourceLimiter, Trap, VMExternRef};
use anyhow::{bail, Result};
use std::cell::{Cell, RefCell};
use std::cmp::min;
use std::convert::TryInto;
use std::ops::Range;
use std::ptr;
use std::rc::Rc;
use wasmtime_environ::wasm::TableElementType;
use wasmtime_environ::{ir, TablePlan};
/// An element going into or coming out of a table.
///
/// Table elements are stored as pointers and are default-initialized with `ptr::null_mut`.
#[derive(Clone, Debug)]
#[derive(Clone)]
pub enum TableElement {
/// A `funcref`.
FuncRef(*mut VMCallerCheckedAnyfunc),
@@ -92,7 +94,6 @@ impl From<VMExternRef> for TableElement {
}
}
#[derive(Debug)]
enum TableStorage {
Static {
data: *mut *mut u8,
@@ -108,38 +109,74 @@ enum TableStorage {
}
/// Represents an instance's table.
#[derive(Debug)]
pub struct Table(TableStorage);
pub struct Table {
storage: TableStorage,
limiter: Option<Rc<dyn ResourceLimiter>>,
}
impl Table {
/// Create a new dynamic (movable) table instance for the specified table plan.
pub fn new_dynamic(plan: &TablePlan) -> Self {
pub fn new_dynamic(
plan: &TablePlan,
limiter: Option<&Rc<dyn ResourceLimiter>>,
) -> Result<Self> {
let elements = RefCell::new(vec![ptr::null_mut(); plan.table.minimum as usize]);
let ty = plan.table.ty.clone();
let maximum = plan.table.maximum;
Self(TableStorage::Dynamic {
let storage = TableStorage::Dynamic {
elements,
ty,
maximum,
})
};
Self::new(plan, storage, limiter)
}
/// Create a new static (immovable) table instance for the specified table plan.
pub fn new_static(plan: &TablePlan, data: *mut *mut u8, maximum: u32) -> Self {
pub fn new_static(
plan: &TablePlan,
data: *mut *mut u8,
maximum: u32,
limiter: Option<&Rc<dyn ResourceLimiter>>,
) -> Result<Self> {
let size = Cell::new(plan.table.minimum);
let ty = plan.table.ty.clone();
let maximum = min(plan.table.maximum.unwrap_or(maximum), maximum);
Self(TableStorage::Static {
let storage = TableStorage::Static {
data,
size,
ty,
maximum,
};
Self::new(plan, storage, limiter)
}
fn new(
plan: &TablePlan,
storage: TableStorage,
limiter: Option<&Rc<dyn ResourceLimiter>>,
) -> Result<Self> {
if let Some(limiter) = limiter {
if !limiter.table_growing(0, plan.table.minimum, plan.table.maximum) {
bail!(
"table minimum size of {} elements exceeds table limits",
plan.table.minimum
);
}
}
Ok(Self {
storage,
limiter: limiter.cloned(),
})
}
/// Returns the type of the elements in this table.
pub fn element_type(&self) -> TableElementType {
match &self.0 {
match &self.storage {
TableStorage::Static { ty, .. } => *ty,
TableStorage::Dynamic { ty, .. } => *ty,
}
@@ -147,7 +184,7 @@ impl Table {
/// Returns whether or not the underlying storage of the table is "static".
pub(crate) fn is_static(&self) -> bool {
if let TableStorage::Static { .. } = &self.0 {
if let TableStorage::Static { .. } = &self.storage {
true
} else {
false
@@ -156,15 +193,20 @@ impl Table {
/// Returns the number of allocated elements.
pub fn size(&self) -> u32 {
match &self.0 {
match &self.storage {
TableStorage::Static { size, .. } => size.get(),
TableStorage::Dynamic { elements, .. } => elements.borrow().len().try_into().unwrap(),
}
}
/// Returns the maximum number of elements.
/// Returns the maximum number of elements at runtime.
///
/// Returns `None` if the table is unbounded.
///
/// The runtime maximum may not be equal to the maximum from the table's Wasm type
/// when it is being constrained by an instance allocator.
pub fn maximum(&self) -> Option<u32> {
match &self.0 {
match &self.storage {
TableStorage::Static { maximum, .. } => Some(*maximum),
TableStorage::Dynamic { maximum, .. } => maximum.clone(),
}
@@ -218,8 +260,14 @@ impl Table {
/// this unsafety.
pub unsafe fn grow(&self, delta: u32, init_value: TableElement) -> Option<u32> {
let old_size = self.size();
let new_size = old_size.checked_add(delta)?;
if let Some(limiter) = &self.limiter {
if !limiter.table_growing(old_size, new_size, self.maximum()) {
return None;
}
}
if let Some(max) = self.maximum() {
if new_size > max {
return None;
@@ -229,7 +277,7 @@ impl Table {
debug_assert!(self.type_matches(&init_value));
// First resize the storage and then fill with the init value
match &self.0 {
match &self.storage {
TableStorage::Static { size, .. } => {
size.set(new_size);
}
@@ -319,7 +367,7 @@ impl Table {
/// Return a `VMTableDefinition` for exposing the table to compiled wasm code.
pub fn vmtable(&self) -> VMTableDefinition {
match &self.0 {
match &self.storage {
TableStorage::Static { data, size, .. } => VMTableDefinition {
base: *data as _,
current_elements: size.get(),
@@ -346,7 +394,7 @@ impl Table {
where
F: FnOnce(&[*mut u8]) -> R,
{
match &self.0 {
match &self.storage {
TableStorage::Static { data, size, .. } => unsafe {
f(std::slice::from_raw_parts(*data, size.get() as usize))
},
@@ -361,7 +409,7 @@ impl Table {
where
F: FnOnce(&mut [*mut u8]) -> R,
{
match &self.0 {
match &self.storage {
TableStorage::Static { data, size, .. } => unsafe {
f(std::slice::from_raw_parts_mut(*data, size.get() as usize))
},
@@ -463,11 +511,14 @@ impl Drop for Table {
// The default table representation is an empty funcref table that cannot grow.
impl Default for Table {
fn default() -> Self {
Self(TableStorage::Static {
data: std::ptr::null_mut(),
size: Cell::new(0),
ty: TableElementType::Func,
maximum: 0,
})
Self {
storage: TableStorage::Static {
data: std::ptr::null_mut(),
size: Cell::new(0),
ty: TableElementType::Func,
maximum: 0,
},
limiter: None,
}
}
}