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use crate::prelude::*;
/// Value returned by [`ResourceLimiter::instances`] default method
pub const DEFAULT_INSTANCE_LIMIT: usize = 10000;
/// Value returned by [`ResourceLimiter::tables`] default method
pub const DEFAULT_TABLE_LIMIT: usize = 10000;
/// Value returned by [`ResourceLimiter::memories`] default method
pub const DEFAULT_MEMORY_LIMIT: usize = 10000;
/// Used by hosts to limit resource consumption of instances.
///
/// This trait is used in conjunction with the
/// [`Store::limiter`](crate::Store::limiter) to synchronously limit the
/// allocation of resources within a store. As a store-level limit this means
/// that all creation of instances, memories, and tables are limited within the
/// store. Resources limited via this trait are primarily related to memory and
/// limiting CPU resources needs to be done with something such as
/// [`Config::consume_fuel`](crate::Config::consume_fuel) or
/// [`Config::epoch_interruption`](crate::Config::epoch_interruption).
///
/// Note that this trait does not limit 100% of memory allocated via a
/// [`Store`](crate::Store). Wasmtime will still allocate memory to track data
/// structures and additionally embedder-specific memory allocations are not
/// tracked via this trait. This trait only limits resources allocated by a
/// WebAssembly instance itself.
///
/// This trait is intended for synchronously limiting the resources of a module.
/// If your use case requires blocking to answer whether a request is permitted
/// or not and you're otherwise working in an asynchronous context the
/// [`ResourceLimiterAsync`] trait is also provided to avoid blocking an OS
/// thread while a limit is determined.
pub trait ResourceLimiter {
/// Notifies the resource limiter that an instance's linear memory has been
/// requested to grow.
///
/// * `current` is the current size of the linear memory in bytes.
/// * `desired` is the desired size of the linear memory in bytes.
/// * `maximum` is either the linear memory's maximum or a maximum from an
/// instance allocator, also in bytes. A value of `None`
/// indicates that the linear memory is unbounded.
///
/// The `current` and `desired` amounts are guaranteed to always be
/// multiples of the WebAssembly page size, 64KiB.
///
/// This function is not invoked when the requested size doesn't fit in
/// `usize`. Additionally this function is not invoked for shared memories
/// at this time. Otherwise even when `desired` exceeds `maximum` this
/// function will still be called.
///
/// ## Return Value
///
/// If `Ok(true)` is returned from this function then the growth operation
/// is allowed. This means that the wasm `memory.grow` instruction will
/// return with the `desired` size, in wasm pages. Note that even if
/// `Ok(true)` is returned, though, if `desired` exceeds `maximum` then the
/// growth operation will still fail.
///
/// If `Ok(false)` is returned then this will cause the `memory.grow`
/// instruction in a module to return -1 (failure), or in the case of an
/// embedder API calling [`Memory::new`](crate::Memory::new) or
/// [`Memory::grow`](crate::Memory::grow) an error will be returned from
/// those methods.
///
/// If `Err(e)` is returned then the `memory.grow` function will behave
/// as if a trap has been raised. Note that this is not necessarily
/// compliant with the WebAssembly specification but it can be a handy and
/// useful tool to get a precise backtrace at "what requested so much memory
/// to cause a growth failure?".
fn memory_growing(
&mut self,
current: usize,
desired: usize,
maximum: Option<usize>,
) -> Result<bool>;
/// Notifies the resource limiter that growing a linear memory, permitted by
/// the `memory_growing` method, has failed.
///
/// Note that this method is not called if `memory_growing` returns an
/// error.
///
/// Reasons for failure include: the growth exceeds the `maximum` passed to
/// `memory_growing`, or the operating system failed to allocate additional
/// memory. In that case, `error` might be downcastable to a `std::io::Error`.
///
/// See the details on the return values for `memory_growing` for what the
/// return value of this function indicates.
fn memory_grow_failed(&mut self, error: anyhow::Error) -> Result<()> {
log::debug!("ignoring memory growth failure error: {error:?}");
Ok(())
}
/// Notifies the resource limiter that an instance's table has been
/// requested to grow.
///
/// * `current` is the current number of elements in the table.
/// * `desired` is the desired number of elements in the table.
/// * `maximum` is either the table's maximum or a maximum from an instance
/// allocator. A value of `None` indicates that the table is unbounded.
///
/// Currently in Wasmtime each table element requires a pointer's worth of
/// space (e.g. `mem::size_of::<usize>()`).
///
/// See the details on the return values for `memory_growing` for what the
/// return value of this function indicates.
fn table_growing(
&mut self,
current: usize,
desired: usize,
maximum: Option<usize>,
) -> Result<bool>;
/// Notifies the resource limiter that growing a linear memory, permitted by
/// the `table_growing` method, has failed.
///
/// Note that this method is not called if `table_growing` returns an error.
///
/// Reasons for failure include: the growth exceeds the `maximum` passed to
/// `table_growing`. This could expand in the future.
///
/// See the details on the return values for `memory_growing` for what the
/// return value of this function indicates.
fn table_grow_failed(&mut self, error: anyhow::Error) -> Result<()> {
log::debug!("ignoring table growth failure error: {error:?}");
Ok(())
}
/// The maximum number of instances that can be created for a `Store`.
///
/// Module instantiation will fail if this limit is exceeded.
///
/// This value defaults to 10,000.
fn instances(&self) -> usize {
DEFAULT_INSTANCE_LIMIT
}
/// The maximum number of tables that can be created for a `Store`.
///
/// Creation of tables will fail if this limit is exceeded.
///
/// This value defaults to 10,000.
fn tables(&self) -> usize {
DEFAULT_TABLE_LIMIT
}
/// The maximum number of linear memories that can be created for a `Store`
///
/// Creation of memories will fail with an error if this limit is exceeded.
///
/// This value defaults to 10,000.
fn memories(&self) -> usize {
DEFAULT_MEMORY_LIMIT
}
}
/// Used by hosts to limit resource consumption of instances, blocking
/// asynchronously if necessary.
///
/// This trait is identical to [`ResourceLimiter`], except that the
/// `memory_growing` and `table_growing` functions are `async`. Must be used
/// with an async [`Store`](`crate::Store`) configured via
/// [`Config::async_support`](crate::Config::async_support).
///
/// This trait is used with
/// [`Store::limiter_async`](`crate::Store::limiter_async`)`: see those docs
/// for restrictions on using other Wasmtime interfaces with an async resource
/// limiter. Additionally see [`ResourceLimiter`] for more information about
/// limiting resources from WebAssembly.
///
/// The `async` here enables embedders that are already using asynchronous
/// execution of WebAssembly to block the WebAssembly, but no the OS thread, to
/// answer the question whether growing a memory or table is allowed.
#[cfg(feature = "async")]
#[async_trait::async_trait]
pub trait ResourceLimiterAsync {
/// Async version of [`ResourceLimiter::memory_growing`]
async fn memory_growing(
&mut self,
current: usize,
desired: usize,
maximum: Option<usize>,
) -> Result<bool>;
/// Identical to [`ResourceLimiter::memory_grow_failed`]
fn memory_grow_failed(&mut self, error: anyhow::Error) -> Result<()> {
log::debug!("ignoring memory growth failure error: {error:?}");
Ok(())
}
/// Asynchronous version of [`ResourceLimiter::table_growing`]
async fn table_growing(
&mut self,
current: usize,
desired: usize,
maximum: Option<usize>,
) -> Result<bool>;
/// Identical to [`ResourceLimiter::table_grow_failed`]
fn table_grow_failed(&mut self, error: anyhow::Error) -> Result<()> {
log::debug!("ignoring table growth failure error: {error:?}");
Ok(())
}
/// Identical to [`ResourceLimiter::instances`]`
fn instances(&self) -> usize {
DEFAULT_INSTANCE_LIMIT
}
/// Identical to [`ResourceLimiter::tables`]`
fn tables(&self) -> usize {
DEFAULT_TABLE_LIMIT
}
/// Identical to [`ResourceLimiter::memories`]`
fn memories(&self) -> usize {
DEFAULT_MEMORY_LIMIT
}
}
/// Used to build [`StoreLimits`].
pub struct StoreLimitsBuilder(StoreLimits);
impl StoreLimitsBuilder {
/// Creates a new [`StoreLimitsBuilder`].
///
/// See the documentation on each builder method for the default for each
/// value.
pub fn new() -> Self {
Self(StoreLimits::default())
}
/// The maximum number of bytes a linear memory can grow to.
///
/// Growing a linear memory beyond this limit will fail. This limit is
/// applied to each linear memory individually, so if a wasm module has
/// multiple linear memories then they're all allowed to reach up to the
/// `limit` specified.
///
/// By default, linear memory will not be limited.
pub fn memory_size(mut self, limit: usize) -> Self {
self.0.memory_size = Some(limit);
self
}
/// The maximum number of elements in a table.
///
/// Growing a table beyond this limit will fail. This limit is applied to
/// each table individually, so if a wasm module has multiple tables then
/// they're all allowed to reach up to the `limit` specified.
///
/// By default, table elements will not be limited.
pub fn table_elements(mut self, limit: usize) -> Self {
self.0.table_elements = Some(limit);
self
}
/// The maximum number of instances that can be created for a [`Store`](crate::Store).
///
/// Module instantiation will fail if this limit is exceeded.
///
/// This value defaults to 10,000.
pub fn instances(mut self, limit: usize) -> Self {
self.0.instances = limit;
self
}
/// The maximum number of tables that can be created for a [`Store`](crate::Store).
///
/// Module instantiation will fail if this limit is exceeded.
///
/// This value defaults to 10,000.
pub fn tables(mut self, tables: usize) -> Self {
self.0.tables = tables;
self
}
/// The maximum number of linear memories that can be created for a [`Store`](crate::Store).
///
/// Instantiation will fail with an error if this limit is exceeded.
///
/// This value defaults to 10,000.
pub fn memories(mut self, memories: usize) -> Self {
self.0.memories = memories;
self
}
/// Indicates that a trap should be raised whenever a growth operation
/// would fail.
///
/// This operation will force `memory.grow` and `table.grow` instructions
/// to raise a trap on failure instead of returning -1. This is not
/// necessarily spec-compliant, but it can be quite handy when debugging a
/// module that fails to allocate memory and might behave oddly as a result.
///
/// This value defaults to `false`.
pub fn trap_on_grow_failure(mut self, trap: bool) -> Self {
self.0.trap_on_grow_failure = trap;
self
}
/// Consumes this builder and returns the [`StoreLimits`].
pub fn build(self) -> StoreLimits {
self.0
}
}
/// Provides limits for a [`Store`](crate::Store).
///
/// This type is created with a [`StoreLimitsBuilder`] and is typically used in
/// conjunction with [`Store::limiter`](crate::Store::limiter).
///
/// This is a convenience type included to avoid needing to implement the
/// [`ResourceLimiter`] trait if your use case fits in the static configuration
/// that this [`StoreLimits`] provides.
#[derive(Clone, Debug)]
pub struct StoreLimits {
memory_size: Option<usize>,
table_elements: Option<usize>,
instances: usize,
tables: usize,
memories: usize,
trap_on_grow_failure: bool,
}
impl Default for StoreLimits {
fn default() -> Self {
Self {
memory_size: None,
table_elements: None,
instances: DEFAULT_INSTANCE_LIMIT,
tables: DEFAULT_TABLE_LIMIT,
memories: DEFAULT_MEMORY_LIMIT,
trap_on_grow_failure: false,
}
}
}
impl ResourceLimiter for StoreLimits {
fn memory_growing(
&mut self,
_current: usize,
desired: usize,
maximum: Option<usize>,
) -> Result<bool> {
let allow = match self.memory_size {
Some(limit) if desired > limit => false,
_ => match maximum {
Some(max) if desired > max => false,
_ => true,
},
};
if !allow && self.trap_on_grow_failure {
bail!("forcing trap when growing memory to {desired} bytes")
} else {
Ok(allow)
}
}
fn memory_grow_failed(&mut self, error: anyhow::Error) -> Result<()> {
if self.trap_on_grow_failure {
Err(error.context("forcing a memory growth failure to be a trap"))
} else {
log::debug!("ignoring memory growth failure error: {error:?}");
Ok(())
}
}
fn table_growing(
&mut self,
_current: usize,
desired: usize,
maximum: Option<usize>,
) -> Result<bool> {
let allow = match self.table_elements {
Some(limit) if desired > limit => false,
_ => match maximum {
Some(max) if desired > max => false,
_ => true,
},
};
if !allow && self.trap_on_grow_failure {
bail!("forcing trap when growing table to {desired} elements")
} else {
Ok(allow)
}
}
fn table_grow_failed(&mut self, error: anyhow::Error) -> Result<()> {
if self.trap_on_grow_failure {
Err(error.context("forcing a table growth failure to be a trap"))
} else {
log::debug!("ignoring table growth failure error: {error:?}");
Ok(())
}
}
fn instances(&self) -> usize {
self.instances
}
fn tables(&self) -> usize {
self.tables
}
fn memories(&self) -> usize {
self.memories
}
}