pezkuwi-subxt/substrate/client/executor/wasmtime/src/util.rs

// This file is part of Substrate.

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.

use crate::{runtime::StoreData, InstantiationStrategy};
use sc_executor_common::{
	error::{Error, Result},
	util::checked_range,
};
use sp_wasm_interface::Pointer;
use wasmtime::{AsContext, AsContextMut};

/// Read data from the instance memory into a slice.
///
/// Returns an error if the read would go out of the memory bounds.
pub(crate) fn read_memory_into(
	ctx: impl AsContext<Data = StoreData>,
	address: Pointer<u8>,
	dest: &mut [u8],
) -> Result<()> {
	let memory = ctx.as_context().data().memory().data(&ctx);

	let range = checked_range(address.into(), dest.len(), memory.len())
		.ok_or_else(|| Error::Other("memory read is out of bounds".into()))?;
	dest.copy_from_slice(&memory[range]);
	Ok(())
}

/// Write data to the instance memory from a slice.
///
/// Returns an error if the write would go out of the memory bounds.
pub(crate) fn write_memory_from(
	mut ctx: impl AsContextMut<Data = StoreData>,
	address: Pointer<u8>,
	data: &[u8],
) -> Result<()> {
	let memory = ctx.as_context().data().memory();
	let memory = memory.data_mut(&mut ctx);

	let range = checked_range(address.into(), data.len(), memory.len())
		.ok_or_else(|| Error::Other("memory write is out of bounds".into()))?;
	memory[range].copy_from_slice(data);
	Ok(())
}

/// Checks whether the `madvise(MADV_DONTNEED)` works as expected.
///
/// In certain environments (e.g. when running under the QEMU user-mode emulator)
/// this syscall is broken.
#[cfg(target_os = "linux")]
fn is_madvise_working() -> std::result::Result<bool, String> {
	let page_size = rustix::param::page_size();

	unsafe {
		// Allocate two memory pages.
		let pointer = rustix::mm::mmap_anonymous(
			std::ptr::null_mut(),
			2 * page_size,
			rustix::mm::ProtFlags::READ | rustix::mm::ProtFlags::WRITE,
			rustix::mm::MapFlags::PRIVATE,
		)
		.map_err(|error| format!("mmap failed: {}", error))?;

		// Dirty them both.
		std::ptr::write_volatile(pointer.cast::<u8>(), b'A');
		std::ptr::write_volatile(pointer.cast::<u8>().add(page_size), b'B');

		// Clear the first page.
		let result_madvise =
			rustix::mm::madvise(pointer, page_size, rustix::mm::Advice::LinuxDontNeed)
				.map_err(|error| format!("madvise failed: {}", error));

		// Fetch the values.
		let value_1 = std::ptr::read_volatile(pointer.cast::<u8>());
		let value_2 = std::ptr::read_volatile(pointer.cast::<u8>().add(page_size));

		let result_munmap = rustix::mm::munmap(pointer, 2 * page_size)
			.map_err(|error| format!("munmap failed: {}", error));

		result_madvise?;
		result_munmap?;

		// Verify that the first page was cleared, while the second one was not.
		Ok(value_1 == 0 && value_2 == b'B')
	}
}

#[cfg(test)]
#[cfg(target_os = "linux")]
#[test]
fn test_is_madvise_working_check_does_not_fail() {
	assert!(is_madvise_working().is_ok());
}

/// Checks whether a given instantiation strategy can be safely used, and replaces
/// it with a slower (but sound) alternative if it isn't.
#[cfg(target_os = "linux")]
pub(crate) fn replace_strategy_if_broken(strategy: &mut InstantiationStrategy) {
	let replacement_strategy = match *strategy {
		// These strategies don't need working `madvise`.
		InstantiationStrategy::Pooling | InstantiationStrategy::RecreateInstance => return,

		// These strategies require a working `madvise` to be sound.
		InstantiationStrategy::PoolingCopyOnWrite => InstantiationStrategy::Pooling,
		InstantiationStrategy::RecreateInstanceCopyOnWrite =>
			InstantiationStrategy::RecreateInstance,
	};

	use std::sync::OnceLock;
	static IS_OK: OnceLock<bool> = OnceLock::new();

	let is_ok = IS_OK.get_or_init(|| {
		let is_ok = match is_madvise_working() {
			Ok(is_ok) => is_ok,
			Err(error) => {
				// This should never happen.
				log::warn!("Failed to check whether `madvise(MADV_DONTNEED)` works: {}", error);
				false
			}
		};

		if !is_ok {
			log::warn!("You're running on a system with a broken `madvise(MADV_DONTNEED)` implementation. This will result in lower performance.");
		}

		is_ok
	});

	if !is_ok {
		*strategy = replacement_strategy;
	}
}

#[cfg(not(target_os = "linux"))]
pub(crate) fn replace_strategy_if_broken(_: &mut InstantiationStrategy) {}