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//! This module provides an allocator to use with the [`alloc`] crate. You can
//! define your own global allocator with the `#[global_allocator]` attribute
//! when not using the `alloc` feature, in case you want to specify your own tag
//! to use with [`ExAllocatePool2`] and [`ExAllocatePoolWithTag`].
use core::alloc::{GlobalAlloc, Layout};
use lazy_static::lazy_static;
use windows_kernel_sys::{
base::_POOL_TYPE as POOL_TYPE,
ntoskrnl::{ExAllocatePool2, ExAllocatePoolWithTag, ExFreePool},
};
use crate::version::VersionInfo;
/// See issue #52191.
#[alloc_error_handler]
fn alloc_error(_: Layout) -> ! {
loop {
x86_64::instructions::hlt()
}
}
lazy_static! {
/// The version of Microsoft Windows that is currently running. This is used by
/// [`KernelAllocator`] to determine whether to use [`ExAllocatePool2`] or
/// [`ExAllocatePoolWithTag`].
static ref VERSION_INFO: VersionInfo = {
VersionInfo::query().unwrap()
};
}
/// Represents a kernel allocator that relies on the `ExAllocatePool` family of
/// functions to allocate and free memory for the `alloc` crate.
pub struct KernelAllocator {
/// The 32-bit tag to use for the pool, this is usually derived from a
/// quadruplet of ASCII bytes, e.g. by invoking
/// `u32::from_ne_bytes(*b"rust")`.
tag: u32,
}
impl KernelAllocator {
/// Sets up a new kernel allocator with the 32-bit tag specified. The tag is
/// usually derived from a quadruplet of ASCII bytes, e.g. by invoking
/// `u32::from_ne_bytes(*b"rust")`.
pub const fn new(tag: u32) -> Self {
Self {
tag,
}
}
}
unsafe impl GlobalAlloc for KernelAllocator {
/// Uses [`ExAllocatePool2`] on Microsoft Windows 10.0.19041 and later, and
/// [`ExAllocatePoolWithTag`] on older versions of Microsoft Windows to
/// allocate memory.
unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
let use_ex_allocate_pool2 = VERSION_INFO.major() > 10
|| (VERSION_INFO.major() == 10 && VERSION_INFO.build_number() == 19041);
let ptr = if use_ex_allocate_pool2 {
ExAllocatePool2(POOL_TYPE::NonPagedPool as _, layout.size() as u64, self.tag)
} else {
ExAllocatePoolWithTag(POOL_TYPE::NonPagedPool, layout.size() as u64, self.tag)
};
if ptr.is_null() {
panic!("[kernel-alloc] failed to allocate pool.");
}
ptr as _
}
/// Uses [`ExFreePool`] to free allocated memory.
unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) { ExFreePool(ptr as _) }
}
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