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refactor: remove UserPtr and UserConstPtr usages #107

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222 changes: 2 additions & 220 deletions api/src/mm.rs
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Original file line number Diff line number Diff line change
@@ -1,10 +1,8 @@
use alloc::string::String;
use core::{
alloc::Layout,
ffi::c_char,
hint::unlikely,
mem::{MaybeUninit, transmute},
ptr, slice, str,
};

use axerrno::{AxError, AxResult};
Expand All @@ -14,226 +12,10 @@ use axhal::{
};
use axio::prelude::*;
use axtask::current;
use memory_addr::{MemoryAddr, PAGE_SIZE_4K, VirtAddr};
use starry_core::{mm::access_user_memory, task::AsThread};
use memory_addr::VirtAddr;
use starry_core::task::AsThread;
use starry_vm::{vm_load_until_nul, vm_read_slice, vm_write_slice};

fn check_region(start: VirtAddr, layout: Layout, access_flags: MappingFlags) -> AxResult<()> {
let align = layout.align();
if start.as_usize() & (align - 1) != 0 {
return Err(AxError::BadAddress);
}

let curr = current();
let mut aspace = curr.as_thread().proc_data.aspace.lock();

if !aspace.can_access_range(start, layout.size(), access_flags) {
return Err(AxError::BadAddress);
}

let page_start = start.align_down_4k();
let page_end = (start + layout.size()).align_up_4k();
aspace.populate_area(page_start, page_end - page_start, access_flags)?;

Ok(())
}

fn check_null_terminated<T: PartialEq + Default>(
start: VirtAddr,
access_flags: MappingFlags,
) -> AxResult<usize> {
let align = Layout::new::<T>().align();
if start.as_usize() & (align - 1) != 0 {
return Err(AxError::BadAddress);
}

let zero = T::default();

let mut page = start.align_down_4k();

let start = start.as_ptr_of::<T>();
let mut len = 0;

access_user_memory(|| {
loop {
// SAFETY: This won't overflow the address space since we'll check
// it below.
let ptr = unsafe { start.add(len) };
while ptr as usize >= page.as_ptr() as usize {
// We cannot prepare `aspace` outside of the loop, since holding
// aspace requires a mutex which would be required on page
// fault, and page faults can trigger inside the loop.

// TODO: this is inefficient, but we have to do this instead of
// querying the page table since the page might has not been
// allocated yet.
let curr = current();
let aspace = curr.as_thread().proc_data.aspace.lock();
if !aspace.can_access_range(page, PAGE_SIZE_4K, access_flags) {
return Err(AxError::BadAddress);
}

page += PAGE_SIZE_4K;
}

// This might trigger a page fault
// SAFETY: The pointer is valid and points to a valid memory region.
if unsafe { ptr.read_volatile() } == zero {
break;
}
len += 1;
}
Ok(())
})?;

Ok(len)
}

/// A pointer to user space memory.
#[repr(transparent)]
#[derive(PartialEq, Clone, Copy)]
pub struct UserPtr<T>(*mut T);

impl<T> From<usize> for UserPtr<T> {
fn from(value: usize) -> Self {
UserPtr(value as *mut _)
}
}

impl<T> From<*mut T> for UserPtr<T> {
fn from(value: *mut T) -> Self {
UserPtr(value)
}
}

impl<T> Default for UserPtr<T> {
fn default() -> Self {
Self(ptr::null_mut())
}
}

impl<T> UserPtr<T> {
const ACCESS_FLAGS: MappingFlags = MappingFlags::READ.union(MappingFlags::WRITE);

pub fn address(&self) -> VirtAddr {
VirtAddr::from_ptr_of(self.0)
}

pub fn cast<U>(self) -> UserPtr<U> {
UserPtr(self.0 as *mut U)
}

pub fn is_null(&self) -> bool {
self.0.is_null()
}

pub fn get_as_mut(self) -> AxResult<&'static mut T> {
check_region(self.address(), Layout::new::<T>(), Self::ACCESS_FLAGS)?;
Ok(unsafe { &mut *self.0 })
}

pub fn get_as_mut_slice(self, len: usize) -> AxResult<&'static mut [T]> {
check_region(
self.address(),
Layout::array::<T>(len).unwrap(),
Self::ACCESS_FLAGS,
)?;
Ok(unsafe { slice::from_raw_parts_mut(self.0, len) })
}

pub fn get_as_mut_null_terminated(self) -> AxResult<&'static mut [T]>
where
T: PartialEq + Default,
{
let len = check_null_terminated::<T>(self.address(), Self::ACCESS_FLAGS)?;
Ok(unsafe { slice::from_raw_parts_mut(self.0, len) })
}
}

/// An immutable pointer to user space memory.
#[repr(transparent)]
#[derive(PartialEq, Clone, Copy)]
pub struct UserConstPtr<T>(*const T);

impl<T> From<usize> for UserConstPtr<T> {
fn from(value: usize) -> Self {
UserConstPtr(value as *const _)
}
}

impl<T> From<*const T> for UserConstPtr<T> {
fn from(value: *const T) -> Self {
UserConstPtr(value)
}
}

impl<T> Default for UserConstPtr<T> {
fn default() -> Self {
Self(ptr::null())
}
}

impl<T> UserConstPtr<T> {
const ACCESS_FLAGS: MappingFlags = MappingFlags::READ;

pub fn address(&self) -> VirtAddr {
VirtAddr::from_ptr_of(self.0)
}

pub fn cast<U>(self) -> UserConstPtr<U> {
UserConstPtr(self.0 as *const U)
}

pub fn is_null(&self) -> bool {
self.0.is_null()
}

pub fn get_as_ref(self) -> AxResult<&'static T> {
check_region(self.address(), Layout::new::<T>(), Self::ACCESS_FLAGS)?;
Ok(unsafe { &*self.0 })
}

pub fn get_as_slice(self, len: usize) -> AxResult<&'static [T]> {
check_region(
self.address(),
Layout::array::<T>(len).unwrap(),
Self::ACCESS_FLAGS,
)?;
Ok(unsafe { slice::from_raw_parts(self.0, len) })
}

pub fn get_as_null_terminated(self) -> AxResult<&'static [T]>
where
T: PartialEq + Default,
{
let len = check_null_terminated::<T>(self.address(), Self::ACCESS_FLAGS)?;
Ok(unsafe { slice::from_raw_parts(self.0, len) })
}
}

impl UserConstPtr<c_char> {
/// Get the pointer as `&str`, validating the memory region.
pub fn get_as_str(self) -> AxResult<&'static str> {
let slice = self.get_as_null_terminated()?;
// SAFETY: c_char is u8
let slice = unsafe { transmute::<&[c_char], &[u8]>(slice) };

str::from_utf8(slice).map_err(|_| AxError::IllegalBytes)
}
}

macro_rules! nullable {
($ptr:ident.$func:ident($($arg:expr),*)) => {
if $ptr.is_null() {
Ok(None)
} else {
Some($ptr.$func($($arg),*)).transpose()
}
};
}

pub(crate) use nullable;

#[register_trap_handler(PAGE_FAULT)]
fn handle_page_fault(vaddr: VirtAddr, access_flags: MappingFlags) -> bool {
debug!("Page fault at {vaddr:#x}, access_flags: {access_flags:#x?}");
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