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// Copyright 2022 The aarch64-paging Authors.
// This project is dual-licensed under Apache 2.0 and MIT terms.
// See LICENSE-APACHE and LICENSE-MIT for details.
//! Functionality for managing page tables with identity mapping.
//!
//! See [`IdMap`] for details on how to use it.
use crate::{
paging::{
deallocate, Attributes, Constraints, Descriptor, MemoryRegion, PageTable, PhysicalAddress,
Translation, VaRange, VirtualAddress,
},
MapError, Mapping,
};
use core::ptr::NonNull;
/// Identity mapping, where every virtual address is either unmapped or mapped to the identical IPA.
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub struct IdTranslation;
impl IdTranslation {
fn virtual_to_physical(va: VirtualAddress) -> PhysicalAddress {
PhysicalAddress(va.0)
}
}
impl Translation for IdTranslation {
fn allocate_table(&self) -> (NonNull<PageTable>, PhysicalAddress) {
let table = PageTable::new();
// Physical address is the same as the virtual address because we are using identity mapping
// everywhere.
(table, PhysicalAddress(table.as_ptr() as usize))
}
unsafe fn deallocate_table(&self, page_table: NonNull<PageTable>) {
deallocate(page_table);
}
fn physical_to_virtual(&self, pa: PhysicalAddress) -> NonNull<PageTable> {
NonNull::new(pa.0 as *mut PageTable).expect("Got physical address 0 for pagetable")
}
}
/// Manages a level 1 page table using identity mapping, where every virtual address is either
/// unmapped or mapped to the identical IPA.
///
/// This assumes that identity mapping is used both for the page table being managed, and for code
/// that is managing it.
///
/// Mappings should be added with [`map_range`](Self::map_range) before calling
/// [`activate`](Self::activate) to start using the new page table. To make changes which may
/// require break-before-make semantics you must first call [`deactivate`](Self::deactivate) to
/// switch back to a previous static page table, and then `activate` again after making the desired
/// changes.
///
/// # Example
///
/// ```no_run
/// use aarch64_paging::{
/// idmap::IdMap,
/// paging::{Attributes, MemoryRegion},
/// };
///
/// const ASID: usize = 1;
/// const ROOT_LEVEL: usize = 1;
///
/// // Create a new page table with identity mapping.
/// let mut idmap = IdMap::new(ASID, ROOT_LEVEL);
/// // Map a 2 MiB region of memory as read-write.
/// idmap.map_range(
/// &MemoryRegion::new(0x80200000, 0x80400000),
/// Attributes::NORMAL | Attributes::NON_GLOBAL | Attributes::VALID,
/// ).unwrap();
/// // SAFETY: Everything the program uses is within the 2 MiB region mapped above.
/// unsafe {
/// // Set `TTBR0_EL1` to activate the page table.
/// idmap.activate();
/// }
///
/// // Write something to the memory...
///
/// // SAFETY: The program will only use memory within the initially mapped region until `idmap` is
/// // reactivated below.
/// unsafe {
/// // Restore `TTBR0_EL1` to its earlier value while we modify the page table.
/// idmap.deactivate();
/// }
/// // Now change the mapping to read-only and executable.
/// idmap.map_range(
/// &MemoryRegion::new(0x80200000, 0x80400000),
/// Attributes::NORMAL | Attributes::NON_GLOBAL | Attributes::READ_ONLY | Attributes::VALID,
/// ).unwrap();
/// // SAFETY: Everything the program will used is mapped in by this page table.
/// unsafe {
/// idmap.activate();
/// }
/// ```
#[derive(Debug)]
pub struct IdMap {
mapping: Mapping<IdTranslation>,
}
impl IdMap {
/// Creates a new identity-mapping page table with the given ASID and root level.
pub fn new(asid: usize, rootlevel: usize) -> Self {
Self {
mapping: Mapping::new(IdTranslation, asid, rootlevel, VaRange::Lower),
}
}
/// Activates the page table by setting `TTBR0_EL1` to point to it, and saves the previous value
/// of `TTBR0_EL1` so that it may later be restored by [`deactivate`](Self::deactivate).
///
/// Panics if a previous value of `TTBR0_EL1` is already saved and not yet used by a call to
/// `deactivate`.
///
/// In test builds or builds that do not target aarch64, the `TTBR0_EL1` access is omitted.
///
/// # Safety
///
/// The caller must ensure that the page table doesn't unmap any memory which the program is
/// using, or introduce aliases which break Rust's aliasing rules. The page table must not be
/// dropped as long as its mappings are required, as it will automatically be deactivated when
/// it is dropped.
pub unsafe fn activate(&mut self) {
self.mapping.activate()
}
/// Deactivates the page table, by setting `TTBR0_EL1` back to the value it had before
/// [`activate`](Self::activate) was called, and invalidating the TLB for this page table's
/// configured ASID.
///
/// Panics if there is no saved `TTBR0_EL1` value because `activate` has not previously been
/// called.
///
/// In test builds or builds that do not target aarch64, the `TTBR0_EL1` access is omitted.
///
/// # Safety
///
/// The caller must ensure that the previous page table which this is switching back to doesn't
/// unmap any memory which the program is using.
pub unsafe fn deactivate(&mut self) {
self.mapping.deactivate()
}
/// Maps the given range of virtual addresses to the identical physical addresses with the given
/// flags.
///
/// This should generally only be called while the page table is not active. In particular, any
/// change that may require break-before-make per the architecture must be made while the page
/// table is inactive. Mapping a previously unmapped memory range may be done while the page
/// table is active. This function writes block and page entries, but only maps them if `flags`
/// contains `Attributes::VALID`, otherwise the entries remain invalid.
///
/// # Errors
///
/// Returns [`MapError::RegionBackwards`] if the range is backwards.
///
/// Returns [`MapError::AddressRange`] if the largest address in the `range` is greater than the
/// largest virtual address covered by the page table given its root level.
///
/// Returns [`MapError::InvalidFlags`] if the `flags` argument has unsupported attributes set.
///
/// Returns [`MapError::BreakBeforeMakeViolation'] if the range intersects with live mappings,
/// and modifying those would violate architectural break-before-make (BBM) requirements.
pub fn map_range(&mut self, range: &MemoryRegion, flags: Attributes) -> Result<(), MapError> {
self.map_range_with_constraints(range, flags, Constraints::empty())
}
/// Maps the given range of virtual addresses to the identical physical addresses with the given
/// given flags, taking the given constraints into account.
///
/// This should generally only be called while the page table is not active. In particular, any
/// change that may require break-before-make per the architecture must be made while the page
/// table is inactive. Mapping a previously unmapped memory range may be done while the page
/// table is active. This function writes block and page entries, but only maps them if `flags`
/// contains `Attributes::VALID`, otherwise the entries remain invalid.
///
/// # Errors
///
/// Returns [`MapError::RegionBackwards`] if the range is backwards.
///
/// Returns [`MapError::AddressRange`] if the largest address in the `range` is greater than the
/// largest virtual address covered by the page table given its root level.
///
/// Returns [`MapError::InvalidFlags`] if the `flags` argument has unsupported attributes set.
///
/// Returns [`MapError::BreakBeforeMakeViolation'] if the range intersects with live mappings,
/// and modifying those would violate architectural break-before-make (BBM) requirements.
pub fn map_range_with_constraints(
&mut self,
range: &MemoryRegion,
flags: Attributes,
constraints: Constraints,
) -> Result<(), MapError> {
let pa = IdTranslation::virtual_to_physical(range.start());
self.mapping.map_range(range, pa, flags, constraints)
}
/// Applies the provided updater function to the page table descriptors covering a given
/// memory range.
///
/// This may involve splitting block entries if the provided range is not currently mapped
/// down to its precise boundaries. For visiting all the descriptors covering a memory range
/// without potential splitting (and no descriptor updates), use
/// [`walk_range`](Self::walk_range) instead.
///
/// The updater function receives the following arguments:
///
/// - The virtual address range mapped by each page table descriptor. A new descriptor will
/// have been allocated before the invocation of the updater function if a page table split
/// was needed.
/// - A mutable reference to the page table descriptor that permits modifications.
/// - The level of a translation table the descriptor belongs to.
///
/// The updater function should return:
///
/// - `Ok` to continue updating the remaining entries.
/// - `Err` to signal an error and stop updating the remaining entries.
///
/// This should generally only be called while the page table is not active. In particular, any
/// change that may require break-before-make per the architecture must be made while the page
/// table is inactive. Mapping a previously unmapped memory range may be done while the page
/// table is active.
///
/// # Errors
///
/// Returns [`MapError::PteUpdateFault`] if the updater function returns an error.
///
/// Returns [`MapError::RegionBackwards`] if the range is backwards.
///
/// Returns [`MapError::AddressRange`] if the largest address in the `range` is greater than the
/// largest virtual address covered by the page table given its root level.
///
/// Returns [`MapError::BreakBeforeMakeViolation'] if the range intersects with live mappings,
/// and modifying those would violate architectural break-before-make (BBM) requirements.
pub fn modify_range<F>(&mut self, range: &MemoryRegion, f: &F) -> Result<(), MapError>
where
F: Fn(&MemoryRegion, &mut Descriptor, usize) -> Result<(), ()> + ?Sized,
{
self.mapping.modify_range(range, f)
}
/// Applies the provided callback function to the page table descriptors covering a given
/// memory range.
///
/// The callback function receives the following arguments:
///
/// - The full virtual address range mapped by each visited page table descriptor, which may
/// exceed the original range passed to `walk_range`, due to alignment to block boundaries.
/// - The page table descriptor itself.
/// - The level of a translation table the descriptor belongs to.
///
/// The callback function should return:
///
/// - `Ok` to continue visiting the remaining entries.
/// - `Err` to signal an error and stop visiting the remaining entries.
///
/// # Errors
///
/// Returns [`MapError::PteUpdateFault`] if the callback function returns an error.
///
/// Returns [`MapError::RegionBackwards`] if the range is backwards.
///
/// Returns [`MapError::AddressRange`] if the largest address in the `range` is greater than the
/// largest virtual address covered by the page table given its root level.
pub fn walk_range<F>(&self, range: &MemoryRegion, f: &mut F) -> Result<(), MapError>
where
F: FnMut(&MemoryRegion, &Descriptor, usize) -> Result<(), ()>,
{
self.mapping.walk_range(range, f)
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::{
paging::{Attributes, MemoryRegion, BITS_PER_LEVEL, PAGE_SIZE},
MapError, VirtualAddress,
};
const MAX_ADDRESS_FOR_ROOT_LEVEL_1: usize = 1 << 39;
#[test]
fn map_valid() {
// A single byte at the start of the address space.
let mut idmap = IdMap::new(1, 1);
// SAFETY: This doesn't actually activate the page table in tests, it just treats it as
// active for the sake of BBM rules.
unsafe {
idmap.activate();
}
assert_eq!(
idmap.map_range(
&MemoryRegion::new(0, 1),
Attributes::NORMAL | Attributes::VALID
),
Ok(())
);
// Two pages at the start of the address space.
let mut idmap = IdMap::new(1, 1);
// SAFETY: This doesn't actually activate the page table in tests, it just treats it as
// active for the sake of BBM rules.
unsafe {
idmap.activate();
}
assert_eq!(
idmap.map_range(
&MemoryRegion::new(0, PAGE_SIZE * 2),
Attributes::NORMAL | Attributes::VALID
),
Ok(())
);
// A single byte at the end of the address space.
let mut idmap = IdMap::new(1, 1);
// SAFETY: This doesn't actually activate the page table in tests, it just treats it as
// active for the sake of BBM rules.
unsafe {
idmap.activate();
}
assert_eq!(
idmap.map_range(
&MemoryRegion::new(
MAX_ADDRESS_FOR_ROOT_LEVEL_1 - 1,
MAX_ADDRESS_FOR_ROOT_LEVEL_1
),
Attributes::NORMAL | Attributes::VALID
),
Ok(())
);
// Two pages, on the boundary between two subtables.
let mut idmap = IdMap::new(1, 1);
// SAFETY: This doesn't actually activate the page table in tests, it just treats it as
// active for the sake of BBM rules.
unsafe {
idmap.activate();
}
assert_eq!(
idmap.map_range(
&MemoryRegion::new(PAGE_SIZE * 1023, PAGE_SIZE * 1025),
Attributes::NORMAL | Attributes::VALID
),
Ok(())
);
// The entire valid address space.
let mut idmap = IdMap::new(1, 1);
// SAFETY: This doesn't actually activate the page table in tests, it just treats it as
// active for the sake of BBM rules.
unsafe {
idmap.activate();
}
assert_eq!(
idmap.map_range(
&MemoryRegion::new(0, MAX_ADDRESS_FOR_ROOT_LEVEL_1),
Attributes::NORMAL | Attributes::VALID
),
Ok(())
);
}
#[test]
fn map_break_before_make() {
const BLOCK_SIZE: usize = PAGE_SIZE << BITS_PER_LEVEL;
let mut idmap = IdMap::new(1, 1);
idmap
.map_range_with_constraints(
&MemoryRegion::new(BLOCK_SIZE, 2 * BLOCK_SIZE),
Attributes::NORMAL | Attributes::VALID,
Constraints::NO_BLOCK_MAPPINGS,
)
.unwrap();
// SAFETY: This doesn't actually activate the page table in tests, it just treats it as
// active for the sake of BBM rules.
unsafe {
idmap.activate();
}
// Splitting a range is permitted if it was mapped down to pages
assert_eq!(
idmap.map_range(
&MemoryRegion::new(BLOCK_SIZE, BLOCK_SIZE + PAGE_SIZE),
Attributes::NORMAL | Attributes::VALID,
),
Ok(())
);
let mut idmap = IdMap::new(1, 1);
idmap
.map_range(
&MemoryRegion::new(BLOCK_SIZE, 2 * BLOCK_SIZE),
Attributes::NORMAL | Attributes::VALID,
)
.ok();
// SAFETY: This doesn't actually activate the page table in tests, it just treats it as
// active for the sake of BBM rules.
unsafe {
idmap.activate();
}
// Extending a range is fine even if there are block mappings
// in the middle
assert_eq!(
idmap.map_range(
&MemoryRegion::new(BLOCK_SIZE - PAGE_SIZE, 2 * BLOCK_SIZE + PAGE_SIZE),
Attributes::NORMAL | Attributes::VALID,
),
Ok(())
);
// Splitting a range is not permitted
assert_eq!(
idmap.map_range(
&MemoryRegion::new(BLOCK_SIZE, BLOCK_SIZE + PAGE_SIZE),
Attributes::NORMAL | Attributes::VALID,
),
Err(MapError::BreakBeforeMakeViolation(MemoryRegion::new(
BLOCK_SIZE,
BLOCK_SIZE + PAGE_SIZE
)))
);
// Remapping a partially live range read-only is only permitted
// if it does not require splitting
assert_eq!(
idmap.map_range(
&MemoryRegion::new(0, BLOCK_SIZE + PAGE_SIZE),
Attributes::NORMAL | Attributes::VALID | Attributes::READ_ONLY,
),
Err(MapError::BreakBeforeMakeViolation(MemoryRegion::new(
0,
BLOCK_SIZE + PAGE_SIZE
)))
);
assert_eq!(
idmap.map_range(
&MemoryRegion::new(0, BLOCK_SIZE),
Attributes::NORMAL | Attributes::VALID | Attributes::READ_ONLY,
),
Ok(())
);
// Changing the memory type is not permitted
assert_eq!(
idmap.map_range(
&MemoryRegion::new(0, BLOCK_SIZE),
Attributes::DEVICE_NGNRE | Attributes::VALID | Attributes::NON_GLOBAL,
),
Err(MapError::BreakBeforeMakeViolation(MemoryRegion::new(
0, BLOCK_SIZE
)))
);
// Making a range invalid is only permitted if it does not require splitting
assert_eq!(
idmap.map_range(
&MemoryRegion::new(PAGE_SIZE, BLOCK_SIZE + PAGE_SIZE),
Attributes::NORMAL,
),
Err(MapError::BreakBeforeMakeViolation(MemoryRegion::new(
PAGE_SIZE,
BLOCK_SIZE + PAGE_SIZE
)))
);
assert_eq!(
idmap.map_range(
&MemoryRegion::new(PAGE_SIZE, BLOCK_SIZE),
Attributes::NORMAL,
),
Ok(())
);
// Creating a new valid entry is always permitted
assert_eq!(
idmap.map_range(
&MemoryRegion::new(0, 2 * PAGE_SIZE),
Attributes::NORMAL | Attributes::VALID,
),
Ok(())
);
// Setting the non-global attribute is permitted
assert_eq!(
idmap.map_range(
&MemoryRegion::new(0, PAGE_SIZE),
Attributes::NORMAL | Attributes::VALID | Attributes::NON_GLOBAL,
),
Ok(())
);
// Removing the non-global attribute from a live mapping is not permitted
assert_eq!(
idmap.map_range(
&MemoryRegion::new(0, PAGE_SIZE),
Attributes::NORMAL | Attributes::VALID,
),
Err(MapError::BreakBeforeMakeViolation(MemoryRegion::new(
0, PAGE_SIZE
)))
);
// SAFETY: This doesn't actually deactivate the page table in tests, it just treats it as
// inactive for the sake of BBM rules.
unsafe {
idmap.deactivate();
}
// Removing the non-global attribute from an inactive mapping is permitted
assert_eq!(
idmap.map_range(
&MemoryRegion::new(0, PAGE_SIZE),
Attributes::NORMAL | Attributes::VALID,
),
Ok(())
);
}
#[test]
fn map_out_of_range() {
let mut idmap = IdMap::new(1, 1);
// One byte, just past the edge of the valid range.
assert_eq!(
idmap.map_range(
&MemoryRegion::new(
MAX_ADDRESS_FOR_ROOT_LEVEL_1,
MAX_ADDRESS_FOR_ROOT_LEVEL_1 + 1,
),
Attributes::NORMAL | Attributes::VALID
),
Err(MapError::AddressRange(VirtualAddress(
MAX_ADDRESS_FOR_ROOT_LEVEL_1 + PAGE_SIZE
)))
);
// From 0 to just past the valid range.
assert_eq!(
idmap.map_range(
&MemoryRegion::new(0, MAX_ADDRESS_FOR_ROOT_LEVEL_1 + 1,),
Attributes::NORMAL | Attributes::VALID
),
Err(MapError::AddressRange(VirtualAddress(
MAX_ADDRESS_FOR_ROOT_LEVEL_1 + PAGE_SIZE
)))
);
}
fn make_map() -> IdMap {
let mut idmap = IdMap::new(1, 1);
idmap
.map_range(
&MemoryRegion::new(0, PAGE_SIZE * 2),
Attributes::NORMAL
| Attributes::NON_GLOBAL
| Attributes::READ_ONLY
| Attributes::VALID,
)
.unwrap();
// SAFETY: This doesn't actually activate the page table in tests, it just treats it as
// active for the sake of BBM rules.
unsafe {
idmap.activate();
}
idmap
}
#[test]
fn update_backwards_range() {
let mut idmap = make_map();
assert!(idmap
.modify_range(
&MemoryRegion::new(PAGE_SIZE * 2, 1),
&|_range, entry, _level| {
entry
.modify_flags(Attributes::SWFLAG_0, Attributes::from_bits(0usize).unwrap());
Ok(())
},
)
.is_err());
}
#[test]
fn update_range() {
let mut idmap = make_map();
assert!(idmap
.modify_range(&MemoryRegion::new(1, PAGE_SIZE), &|_range, entry, level| {
if level == 3 || !entry.is_table_or_page() {
entry.modify_flags(Attributes::SWFLAG_0, Attributes::NON_GLOBAL);
}
Ok(())
})
.is_err());
idmap
.modify_range(&MemoryRegion::new(1, PAGE_SIZE), &|_range, entry, level| {
if level == 3 || !entry.is_table_or_page() {
entry
.modify_flags(Attributes::SWFLAG_0, Attributes::from_bits(0usize).unwrap());
}
Ok(())
})
.unwrap();
idmap
.modify_range(&MemoryRegion::new(1, PAGE_SIZE), &|range, entry, level| {
if level == 3 || !entry.is_table_or_page() {
assert!(entry.flags().unwrap().contains(Attributes::SWFLAG_0));
assert_eq!(range.end() - range.start(), PAGE_SIZE);
}
Ok(())
})
.unwrap();
}
#[test]
fn breakup_invalid_block() {
const BLOCK_RANGE: usize = 0x200000;
let mut idmap = IdMap::new(1, 1);
// SAFETY: This doesn't actually activate the page table in tests, it just treats it as
// active for the sake of BBM rules.
unsafe {
idmap.activate();
}
idmap
.map_range(
&MemoryRegion::new(0, BLOCK_RANGE),
Attributes::NORMAL | Attributes::NON_GLOBAL | Attributes::SWFLAG_0,
)
.unwrap();
idmap
.map_range(
&MemoryRegion::new(0, PAGE_SIZE),
Attributes::NORMAL | Attributes::NON_GLOBAL | Attributes::VALID,
)
.unwrap();
idmap
.modify_range(
&MemoryRegion::new(0, BLOCK_RANGE),
&|range, entry, level| {
if level == 3 {
let has_swflag = entry.flags().unwrap().contains(Attributes::SWFLAG_0);
let is_first_page = range.start().0 == 0usize;
assert!(has_swflag != is_first_page);
}
Ok(())
},
)
.unwrap();
}
}