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// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.
//! Interfaces to read and write guest memory.
// UNSAFETY: This crate's whole purpose is manual memory mapping and management.
#![allow(unsafe_code)]
pub mod ranges;
use self::ranges::PagedRange;
use inspect::Inspect;
use pal_event::Event;
use sparse_mmap::AsMappableRef;
use std::fmt::Debug;
use std::io;
use std::ops::Deref;
use std::ops::Range;
use std::ptr::NonNull;
use std::sync::atomic::AtomicU8;
use std::sync::atomic::Ordering;
use std::sync::Arc;
use thiserror::Error;
use zerocopy::AsBytes;
use zerocopy::FromBytes;
use zerocopy::FromZeroes;
// Effective page size for page-related operations in this crate.
pub const PAGE_SIZE: usize = 4096;
const PAGE_SIZE64: u64 = 4096;
/// A memory access error returned by one of the [`GuestMemory`] methods.
#[derive(Debug, Error)]
#[error(transparent)]
pub struct GuestMemoryError(Box<GuestMemoryErrorInner>);
impl GuestMemoryError {
fn new(
debug_name: &Arc<str>,
range: Option<Range<u64>>,
op: GuestMemoryOperation,
err: GuestMemoryBackingError,
) -> Self {
GuestMemoryError(Box::new(GuestMemoryErrorInner {
op,
debug_name: debug_name.clone(),
range,
gpa: (err.gpa != INVALID_ERROR_GPA).then_some(err.gpa),
err: err.err,
}))
}
}
#[derive(Debug, Copy, Clone)]
enum GuestMemoryOperation {
Read,
Write,
Fill,
CompareExchange,
Lock,
Subrange,
Probe,
}
impl std::fmt::Display for GuestMemoryOperation {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.pad(match self {
GuestMemoryOperation::Read => "read",
GuestMemoryOperation::Write => "write",
GuestMemoryOperation::Fill => "fill",
GuestMemoryOperation::CompareExchange => "compare exchange",
GuestMemoryOperation::Lock => "lock",
GuestMemoryOperation::Subrange => "subrange",
GuestMemoryOperation::Probe => "probe",
})
}
}
#[derive(Debug, Error)]
struct GuestMemoryErrorInner {
op: GuestMemoryOperation,
debug_name: Arc<str>,
range: Option<Range<u64>>,
gpa: Option<u64>,
#[source]
err: Box<dyn std::error::Error + Send + Sync>,
}
impl std::fmt::Display for GuestMemoryErrorInner {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
write!(
f,
"guest memory '{debug_name}': {op} error: failed to access ",
debug_name = self.debug_name,
op = self.op
)?;
if let Some(range) = &self.range {
write!(f, "{:#x}-{:#x}", range.start, range.end)?;
} else {
f.write_str("memory")?;
}
// Include the precise GPA if provided and different from the start of
// the range.
if let Some(gpa) = self.gpa {
if self.range.as_ref().map_or(true, |range| range.start != gpa) {
write!(f, " at {:#x}", gpa)?;
}
}
Ok(())
}
}
/// A memory access error returned by a [`GuestMemoryAccess`] trait method.
#[derive(Debug)]
pub struct GuestMemoryBackingError {
gpa: u64,
err: Box<dyn std::error::Error + Send + Sync>,
}
/// Used to avoid needing an `Option` for [`GuestMemoryBackingError::gpa`], to
/// save size in hot paths.
const INVALID_ERROR_GPA: u64 = !0;
impl GuestMemoryBackingError {
/// Returns a new error for a memory access failure at address `gpa`.
pub fn new(gpa: u64, err: impl Into<Box<dyn std::error::Error + Send + Sync>>) -> Self {
// `gpa` might incorrectly be INVALID_ERROR_GPA; this is harmless (just
// affecting the error message), so don't assert on it in case this is
// an untrusted value in some path.
Self {
gpa,
err: err.into(),
}
}
fn gpn(err: InvalidGpn) -> Self {
Self {
gpa: INVALID_ERROR_GPA,
err: err.into(),
}
}
}
#[derive(Debug, Error)]
#[error("no memory at address")]
struct OutOfRange;
#[derive(Debug, Error)]
#[error("memory not lockable")]
struct NotLockable;
#[derive(Debug, Error)]
#[error("no fallback for this operation")]
struct NoFallback;
#[derive(Debug, Error)]
#[error("the specified page is not mapped")]
struct NotMapped;
#[derive(Debug, Error)]
#[error("page inaccessible in bitmap")]
struct BitmapFailure;
/// A trait for a guest memory backing that is fully available via a virtual
/// address mapping, as opposed to the fallback functions such as
/// [`GuestMemoryAccess::read_fallback`].
///
/// By implementing this trait, a type guarantees that its
/// [`GuestMemoryAccess::mapping`] will return `Some(_)` and that all of its
/// memory can be accessed through that mapping, without needing to call the
/// fallback functions.
pub trait LinearGuestMemory: GuestMemoryAccess {}
// SAFETY: the allocation will stay valid for the lifetime of the object.
unsafe impl GuestMemoryAccess for sparse_mmap::alloc::SharedMem {
fn mapping(&self) -> Option<NonNull<u8>> {
NonNull::new(self.as_ptr().cast_mut().cast())
}
fn max_address(&self) -> u64 {
self.len() as u64
}
}
impl LinearGuestMemory for sparse_mmap::alloc::SharedMem {}
/// A page-aligned heap allocation for use with [`GuestMemory`].
pub struct AlignedHeapMemory {
pages: Box<[AlignedPage]>,
}
impl Debug for AlignedHeapMemory {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_struct("AlignedHeapMemory")
.field("len", &self.len())
.finish()
}
}
#[repr(C, align(4096))]
struct AlignedPage([AtomicU8; PAGE_SIZE]);
impl AlignedHeapMemory {
/// Allocates a new memory of `size` bytes, rounded up to a page size.
pub fn new(size: usize) -> Self {
#[allow(clippy::declare_interior_mutable_const)] // <https://github.com/rust-lang/rust-clippy/issues/7665>
const ZERO: AtomicU8 = AtomicU8::new(0);
#[allow(clippy::declare_interior_mutable_const)]
const ZERO_PAGE: AlignedPage = AlignedPage([ZERO; PAGE_SIZE]);
let mut pages = Vec::new();
pages.resize_with((size + PAGE_SIZE - 1) / PAGE_SIZE, || ZERO_PAGE);
Self {
pages: pages.into(),
}
}
/// Returns the length of the memory in bytes.
pub fn len(&self) -> usize {
self.pages.len() * PAGE_SIZE
}
}
impl Deref for AlignedHeapMemory {
type Target = [AtomicU8];
fn deref(&self) -> &Self::Target {
// SAFETY: the buffer has the correct size and validity.
unsafe { std::slice::from_raw_parts(self.pages.as_ptr().cast(), self.len()) }
}
}
impl AsRef<[AtomicU8]> for AlignedHeapMemory {
fn as_ref(&self) -> &[AtomicU8] {
self
}
}
// SAFETY: the allocation remains alive and valid for the lifetime of the
// object.
unsafe impl GuestMemoryAccess for AlignedHeapMemory {
fn mapping(&self) -> Option<NonNull<u8>> {
NonNull::new(self.pages.as_ptr().cast_mut().cast())
}
fn max_address(&self) -> u64 {
(self.pages.len() * PAGE_SIZE) as u64
}
}
impl LinearGuestMemory for AlignedHeapMemory {}
/// A trait for a guest memory backing.
///
/// Guest memory may be backed by a virtual memory mapping, in which case this
/// trait can provide the VA and length of that mapping. Alternatively, it may
/// be backed by some other means, in which case this trait can provide fallback
/// methods for reading and writing memory.
///
/// Memory access should first be attempted via the virtual address mapping. If
/// this fails or is not present, the caller should fall back to `read_fallback`
/// or `write_fallback`. This allows an implementation to have a fast path using
/// the mapping, and a slow path using the fallback functions.
///
/// # Safety
///
/// The implementor must follow the contract for each method.
pub unsafe trait GuestMemoryAccess: 'static + Send + Sync {
/// Returns a stable VA mapping for guest memory.
///
/// The size of the mapping is the same as `max_address`.
///
/// The VA is guaranteed to remain reserved, but individual ranges may be
/// uncommitted.
fn mapping(&self) -> Option<NonNull<u8>>;
/// The maximum address that can be passed to the `*_fallback` methods, as
/// well as the maximum offset into the VA range described by `mapping`.
fn max_address(&self) -> u64;
/// The bitmaps to check for validity, one bit per page. If a bit is set,
/// then the page is valid to access via the mapping; if it is clear, then
/// the page will not be accessed.
///
/// The bitmaps must be at least `ceil(bitmap_start + max_address() /
/// PAGE_SIZE)` bits long, and they must be valid for atomic read access for
/// the lifetime of this object from any thread.
///
/// The bitmaps are only checked if there is a mapping. If the bitmap check
/// fails, then the associated `*_fallback` routine is called to handle the
/// error.
///
/// TODO: add a synchronization scheme.
fn access_bitmap(&self) -> Option<BitmapInfo> {
None
}
// Returns an accessor for a subrange, or `None` to use the default
// implementation.
fn subrange(
&self,
offset: u64,
len: u64,
allow_preemptive_locking: bool,
) -> Result<Option<GuestMemory>, GuestMemoryBackingError> {
let _ = (offset, len, allow_preemptive_locking);
Ok(None)
}
/// Called when access to memory via the mapped range fails, either due to a
/// bitmap failure or due to a failure when accessing the virtual address.
///
/// `address` is the address where the access failed. `len` is the remainder
/// of the access; it is not necessarily the case that all `len` bytes are
/// inaccessible in the bitmap or mapping.
///
/// Returns whether the faulting operation should be retried, failed, or that
/// one of the fallback operations (e.g. `read_fallback`) should be called.
fn page_fault(
&self,
address: u64,
len: usize,
write: bool,
bitmap_failure: bool,
) -> PageFaultAction {
let _ = (address, len, write);
if bitmap_failure {
PageFaultAction::Fail(BitmapFailure.into())
} else {
PageFaultAction::Fail(NotMapped.into())
}
}
/// Fallback called if a read fails via direct access to `mapped_range`.
///
/// This is only called if `mapping()` returns `None` or if `page_fault()`
/// returns `PageFaultAction::Fallback`.
///
/// Implementors must ensure that `dest[..len]` is fully initialized on
/// successful return.
///
/// # Safety
/// The caller must ensure that `dest[..len]` is valid for write. Note,
/// however, that `dest` might be aliased by other threads, the guest, or
/// the kernel.
unsafe fn read_fallback(
&self,
addr: u64,
dest: *mut u8,
len: usize,
) -> Result<(), GuestMemoryBackingError> {
let _ = (dest, len);
Err(GuestMemoryBackingError::new(addr, NoFallback))
}
/// Fallback called if a write fails via direct access to `mapped_range`.
///
/// This is only called if `mapping()` returns `None` or if `page_fault()`
/// returns `PageFaultAction::Fallback`.
///
/// # Safety
/// The caller must ensure that `src[..len]` is valid for read. Note,
/// however, that `src` might be aliased by other threads, the guest, or
/// the kernel.
unsafe fn write_fallback(
&self,
addr: u64,
src: *const u8,
len: usize,
) -> Result<(), GuestMemoryBackingError> {
let _ = (src, len);
Err(GuestMemoryBackingError::new(addr, NoFallback))
}
/// Fallback called if a fill fails via direct access to `mapped_range`.
///
/// This is only called if `mapping()` returns `None` or if `page_fault()`
/// returns `PageFaultAction::Fallback`.
fn fill_fallback(&self, addr: u64, val: u8, len: usize) -> Result<(), GuestMemoryBackingError> {
let _ = (val, len);
Err(GuestMemoryBackingError::new(addr, NoFallback))
}
/// Fallback called if a compare exchange fails via direct access to `mapped_range`.
///
/// On compare failure, returns `Ok(false)` and updates `current`.
///
/// This is only called if `mapping()` returns `None` or if `page_fault()`
/// returns `PageFaultAction::Fallback`.
fn compare_exchange_fallback(
&self,
addr: u64,
current: &mut [u8],
new: &[u8],
) -> Result<bool, GuestMemoryBackingError> {
let _ = (current, new);
Err(GuestMemoryBackingError::new(addr, NoFallback))
}
/// Prepares a guest page for having its virtual address exposed as part of
/// a lock call.
///
/// This is useful to ensure that the address is mapped in a way that it can
/// be passed to the kernel for DMA.
fn expose_va(&self, address: u64, len: u64) -> Result<(), GuestMemoryBackingError> {
let _ = (address, len);
Ok(())
}
/// Returns the base IO virtual address for the mapping.
///
/// This is the base address that should be used for DMA from a user-mode
/// device driver whose device is not otherwise configured to go through an
/// IOMMU.
fn base_iova(&self) -> Option<u64> {
None
}
}
/// The action to take after [`GuestMemoryAccess::page_fault`] returns to
/// continue the operation.
pub enum PageFaultAction {
/// Fail the operation.
Fail(Box<dyn std::error::Error + Send + Sync>),
/// Retry the operation.
Retry,
/// Use the fallback method to access the memory.
Fallback,
}
/// Returned by [`GuestMemoryAccess::access_bitmap`].
pub struct BitmapInfo {
/// A pointer to the bitmap for read access.
pub read_bitmap: NonNull<u8>,
/// A pointer to the bitmap for write access.
pub write_bitmap: NonNull<u8>,
/// A pointer to the bitmap for execute access.
pub execute_bitmap: NonNull<u8>,
/// The bit offset of the beginning of the bitmap.
///
/// Typically this is zero, but it is needed to support subranges that are
/// not 8-page multiples.
pub bit_offset: u8,
}
// SAFETY: passing through guarantees from `T`.
unsafe impl<T: GuestMemoryAccess> GuestMemoryAccess for Arc<T> {
fn mapping(&self) -> Option<NonNull<u8>> {
self.as_ref().mapping()
}
fn max_address(&self) -> u64 {
self.as_ref().max_address()
}
fn access_bitmap(&self) -> Option<BitmapInfo> {
self.as_ref().access_bitmap()
}
fn subrange(
&self,
offset: u64,
len: u64,
allow_preemptive_locking: bool,
) -> Result<Option<GuestMemory>, GuestMemoryBackingError> {
self.as_ref()
.subrange(offset, len, allow_preemptive_locking)
}
fn page_fault(
&self,
addr: u64,
len: usize,
write: bool,
bitmap_failure: bool,
) -> PageFaultAction {
self.as_ref().page_fault(addr, len, write, bitmap_failure)
}
unsafe fn read_fallback(
&self,
addr: u64,
dest: *mut u8,
len: usize,
) -> Result<(), GuestMemoryBackingError> {
// SAFETY: passing through guarantees from caller.
unsafe { self.as_ref().read_fallback(addr, dest, len) }
}
unsafe fn write_fallback(
&self,
addr: u64,
src: *const u8,
len: usize,
) -> Result<(), GuestMemoryBackingError> {
// SAFETY: passing through guarantees from caller.
unsafe { self.as_ref().write_fallback(addr, src, len) }
}
fn fill_fallback(&self, addr: u64, val: u8, len: usize) -> Result<(), GuestMemoryBackingError> {
self.as_ref().fill_fallback(addr, val, len)
}
fn compare_exchange_fallback(
&self,
addr: u64,
current: &mut [u8],
new: &[u8],
) -> Result<bool, GuestMemoryBackingError> {
self.as_ref().compare_exchange_fallback(addr, current, new)
}
fn expose_va(&self, address: u64, len: u64) -> Result<(), GuestMemoryBackingError> {
self.as_ref().expose_va(address, len)
}
fn base_iova(&self) -> Option<u64> {
self.as_ref().base_iova()
}
}
// SAFETY: the allocation will stay valid for the lifetime of the object.
unsafe impl GuestMemoryAccess for sparse_mmap::SparseMapping {
fn mapping(&self) -> Option<NonNull<u8>> {
NonNull::new(self.as_ptr().cast())
}
fn max_address(&self) -> u64 {
self.len() as u64
}
}
/// Default guest memory range type, enforcing access boundaries.
struct GuestMemoryAccessRange {
base: Arc<GuestMemoryInner>,
offset: u64,
len: u64,
region: usize,
}
impl GuestMemoryAccessRange {
fn adjust_range(&self, address: u64, len: u64) -> Result<u64, GuestMemoryBackingError> {
if address <= self.len && len <= self.len - address {
Ok(self.offset + address)
} else {
Err(GuestMemoryBackingError::new(address, OutOfRange))
}
}
}
// SAFETY: `mapping()` is guaranteed to be valid for the lifetime of the object.
unsafe impl GuestMemoryAccess for GuestMemoryAccessRange {
fn mapping(&self) -> Option<NonNull<u8>> {
let region = &self.base.regions[self.region];
region.mapping.and_then(|mapping| {
let offset = self.offset & self.base.region_def.region_mask;
// This is guaranteed by construction.
assert!(region.len >= offset + self.len);
// SAFETY: this mapping is guaranteed to be within range by
// construction (and validated again via the assertion above).
NonNull::new(unsafe { mapping.0.as_ptr().add(offset as usize) })
})
}
fn max_address(&self) -> u64 {
self.len
}
fn access_bitmap(&self) -> Option<BitmapInfo> {
let region = &self.base.regions[self.region];
region.bitmaps.map(|bitmaps| {
let offset = self.offset & self.base.region_def.region_mask;
let bit_offset = region.bitmap_start as u64 + offset / PAGE_SIZE64;
let [read_bitmap, write_bitmap, execute_bitmap] = bitmaps.map(|SendPtrU8(ptr)| {
// SAFETY: the bitmap is guaranteed to be big enough for the region
// by construction.
NonNull::new(unsafe { ptr.as_ptr().add((bit_offset / 8) as usize) }).unwrap()
});
let bitmap_start = (bit_offset % 8) as u8;
BitmapInfo {
read_bitmap,
write_bitmap,
execute_bitmap,
bit_offset: bitmap_start,
}
})
}
fn subrange(
&self,
offset: u64,
len: u64,
_allow_preemptive_locking: bool,
) -> Result<Option<GuestMemory>, GuestMemoryBackingError> {
let address = self.adjust_range(offset, len)?;
Ok(Some(GuestMemory::new(
self.base.debug_name.clone(),
GuestMemoryAccessRange {
base: self.base.clone(),
offset: address,
len,
region: self.region,
},
)))
}
fn page_fault(
&self,
address: u64,
len: usize,
write: bool,
bitmap_failure: bool,
) -> PageFaultAction {
let address = self
.adjust_range(address, len as u64)
.expect("the caller should have validated the range was in the mapping");
self.base
.imp
.page_fault(address, len, write, bitmap_failure)
}
unsafe fn write_fallback(
&self,
address: u64,
src: *const u8,
len: usize,
) -> Result<(), GuestMemoryBackingError> {
let address = self.adjust_range(address, len as u64)?;
// SAFETY: guaranteed by caller.
unsafe { self.base.imp.write_fallback(address, src, len) }
}
fn fill_fallback(
&self,
address: u64,
val: u8,
len: usize,
) -> Result<(), GuestMemoryBackingError> {
let address = self.adjust_range(address, len as u64)?;
self.base.imp.fill_fallback(address, val, len)
}
fn compare_exchange_fallback(
&self,
addr: u64,
current: &mut [u8],
new: &[u8],
) -> Result<bool, GuestMemoryBackingError> {
let address = self.adjust_range(addr, new.len() as u64)?;
self.base
.imp
.compare_exchange_fallback(address, current, new)
}
unsafe fn read_fallback(
&self,
address: u64,
dest: *mut u8,
len: usize,
) -> Result<(), GuestMemoryBackingError> {
let address = self.adjust_range(address, len as u64)?;
// SAFETY: guaranteed by caller.
unsafe { self.base.imp.read_fallback(address, dest, len) }
}
fn expose_va(&self, address: u64, len: u64) -> Result<(), GuestMemoryBackingError> {
let address = self.adjust_range(address, len)?;
self.base.imp.expose_va(address, len)
}
fn base_iova(&self) -> Option<u64> {
let region = &self.base.regions[self.region];
Some(region.base_iova? + (self.offset & self.base.region_def.region_mask))
}
}
/// Create a default guest memory subrange that verifies range limits and calls
/// back into the base implementation.
fn create_memory_subrange(
base: Arc<GuestMemoryInner>,
offset: u64,
len: u64,
_allow_preemptive_locking: bool,
) -> Result<GuestMemory, GuestMemoryBackingError> {
let (_, _, region) = base.region(offset, len)?;
Ok(GuestMemory::new(
base.debug_name.clone(),
GuestMemoryAccessRange {
base,
offset,
len,
region,
},
))
}
struct MultiRegionGuestMemoryAccess<T> {
imps: Vec<Option<T>>,
region_def: RegionDefinition,
}
impl<T> MultiRegionGuestMemoryAccess<T> {
fn region(&self, gpa: u64, len: u64) -> Result<(&T, u64), GuestMemoryBackingError> {
let (i, offset) = self.region_def.region(gpa, len)?;
let imp = self.imps[i]
.as_ref()
.ok_or(GuestMemoryBackingError::new(gpa, OutOfRange))?;
Ok((imp, offset))
}
}
// SAFETY: `mapping()` is unreachable and panics if called.
unsafe impl<T: GuestMemoryAccess> GuestMemoryAccess for MultiRegionGuestMemoryAccess<T> {
fn mapping(&self) -> Option<NonNull<u8>> {
unreachable!()
}
fn max_address(&self) -> u64 {
unreachable!()
}
fn access_bitmap(&self) -> Option<BitmapInfo> {
unreachable!()
}
fn subrange(
&self,
offset: u64,
len: u64,
allow_preemptive_locking: bool,
) -> Result<Option<GuestMemory>, GuestMemoryBackingError> {
let (region, offset_in_region) = self.region(offset, len)?;
region.subrange(offset_in_region, len, allow_preemptive_locking)
}
unsafe fn read_fallback(
&self,
addr: u64,
dest: *mut u8,
len: usize,
) -> Result<(), GuestMemoryBackingError> {
let (region, offset_in_region) = self.region(addr, len as u64)?;
// SAFETY: guaranteed by caller.
unsafe { region.read_fallback(offset_in_region, dest, len) }
}
unsafe fn write_fallback(
&self,
addr: u64,
src: *const u8,
len: usize,
) -> Result<(), GuestMemoryBackingError> {
let (region, offset_in_region) = self.region(addr, len as u64)?;
// SAFETY: guaranteed by caller.
unsafe { region.write_fallback(offset_in_region, src, len) }
}
fn fill_fallback(&self, addr: u64, val: u8, len: usize) -> Result<(), GuestMemoryBackingError> {
let (region, offset_in_region) = self.region(addr, len as u64)?;
region.fill_fallback(offset_in_region, val, len)
}
fn compare_exchange_fallback(
&self,
addr: u64,
current: &mut [u8],
new: &[u8],
) -> Result<bool, GuestMemoryBackingError> {
let (region, offset_in_region) = self.region(addr, new.len() as u64)?;
region.compare_exchange_fallback(offset_in_region, current, new)
}
fn expose_va(&self, address: u64, len: u64) -> Result<(), GuestMemoryBackingError> {
let (region, offset_in_region) = self.region(address, len)?;
region.expose_va(offset_in_region, len)
}
fn base_iova(&self) -> Option<u64> {
unreachable!()
}
}
/// A wrapper around a `GuestMemoryAccess` that provides methods for safely
/// reading and writing guest memory.
// NOTE: this type uses `inspect(skip)`, as it end up being a dependency of
// _many_ objects, and littering the inspect graph with references to the same
// node would be silly.
#[derive(Debug, Clone, Inspect)]
#[inspect(skip)]
pub struct GuestMemory {
inner: Arc<GuestMemoryInner>,
}
struct GuestMemoryInner<T: ?Sized = dyn GuestMemoryAccess> {
region_def: RegionDefinition,
regions: Vec<MemoryRegion>,
debug_name: Arc<str>,
imp: T,
}
impl<T: ?Sized> Debug for GuestMemoryInner<T> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_struct("GuestMemoryInner")
.field("region_def", &self.region_def)
.field("regions", &self.regions)
.finish()
}
}
#[derive(Debug, Copy, Clone, Default)]
struct MemoryRegion {
mapping: Option<SendPtrU8>,
bitmaps: Option<[SendPtrU8; 3]>,
bitmap_start: u8,
len: u64,
base_iova: Option<u64>,
}
/// The access type. The values correspond to bitmap indexes.
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
enum AccessType {
Read = 0,
Write = 1,
// FUTURE: add method to read for execute permission.
_Execute = 2,
}
/// `NonNull<u8>` that implements `Send+Sync`.
///
/// Rust makes pointers `!Send+!Sync` by default to force you to think about the
/// ownership model and thread safety of types using pointers--there is nothing
/// safety-related about `Send`/`Sync` on pointers by themselves since all such
/// accesses to pointers require `unsafe` blocks anyway.
///
/// However, in practice, this leads to spurious manual `Send+Sync` impls on
/// types containing pointers, especially those containing generics. Define a
/// wrapping pointer type that implements `Send+Sync` so that the normal auto
/// trait rules apply to types containing these pointers.
#[derive(Debug, Copy, Clone)]
struct SendPtrU8(NonNull<u8>);
// SAFETY: see type description.
unsafe impl Send for SendPtrU8 {}
// SAFETY: see type description.
unsafe impl Sync for SendPtrU8 {}
impl MemoryRegion {
fn new(imp: &impl GuestMemoryAccess) -> Self {
let bitmap_info = imp.access_bitmap();
let bitmaps = bitmap_info.as_ref().map(|bm| {
[
SendPtrU8(bm.read_bitmap),
SendPtrU8(bm.write_bitmap),
SendPtrU8(bm.execute_bitmap),
]
});
let bitmap_start = bitmap_info.map_or(0, |bi| bi.bit_offset);
Self {
mapping: imp.mapping().map(SendPtrU8),
bitmaps,
bitmap_start,
len: imp.max_address(),
base_iova: imp.base_iova(),
}
}
// # Safety
//
// The caller must ensure that `offset + len` fits in this region, and that
// the object bitmap is currently valid for atomic read access from this
// thread.
unsafe fn check_access(
&self,
access_type: AccessType,
offset: u64,
len: u64,
) -> Result<(), u64> {
debug_assert!(self.len >= offset + len);
if let Some(bitmaps) = &self.bitmaps {
let SendPtrU8(bitmap) = bitmaps[access_type as usize];
let start = offset / PAGE_SIZE64;
let end = (offset + len - 1) / PAGE_SIZE64;
// FUTURE: consider optimizing this separately for multi-page and
// single-page accesses.
for gpn in start..=end {
let bit_offset = self.bitmap_start as u64 + gpn;
// SAFETY: the caller ensures that the bitmap is big enough and
// valid for atomic read access from this thread.
let bit = unsafe {
(*bitmap
.as_ptr()
.cast_const()
.cast::<AtomicU8>()
.add(bit_offset as usize / 8))
.load(Ordering::Relaxed)
& (1 << (bit_offset % 8))
};
if bit == 0 {
return Err((gpn * PAGE_SIZE64).saturating_sub(offset));
}
}
}
Ok(())
}
}
/// The default implementation is [`GuestMemory::empty`].
impl Default for GuestMemory {
fn default() -> Self {
Self::empty()
}
}
struct Empty;
// SAFETY: the mapping is empty, so all requirements are trivially satisfied.
unsafe impl GuestMemoryAccess for Empty {
fn mapping(&self) -> Option<NonNull<u8>> {
None
}
fn max_address(&self) -> u64 {
0
}
}
#[derive(Debug, Error)]
pub enum MultiRegionError {
#[error("region size {0:#x} is not a power of 2")]
NotPowerOfTwo(u64),
#[error("region size {0:#x} is smaller than a page")]
RegionSizeTooSmall(u64),
#[error("too many regions ({region_count}) for region size {region_size:#x}; max is {max_region_count}")]
TooManyRegions {
region_count: usize,
max_region_count: usize,
region_size: u64,
},
#[error("backing size {backing_size:#x} is too large for region size {region_size:#x}")]
BackingTooLarge { backing_size: u64, region_size: u64 },
}
impl GuestMemory {
/// Returns a new instance using `imp` as the backing.
///
/// `debug_name` is used to specify which guest memory is being accessed in
/// error messages.
pub fn new(debug_name: impl Into<Arc<str>>, imp: impl GuestMemoryAccess) -> Self {
// Install signal handlers on unix.
sparse_mmap::initialize_try_copy();
let regions = vec![MemoryRegion::new(&imp)];
Self {
inner: Arc::new(GuestMemoryInner {
imp,
debug_name: debug_name.into(),
region_def: RegionDefinition {
invalid_mask: 1 << 63,
region_mask: !0 >> 1,
region_bits: 63, // right shift of 64 isn't valid, so restrict the space
},
regions,
}),
}
}
/// Creates a new multi-region guest memory, made up of multiple mappings.
/// This allows you to create a very large sparse layout (up to the limits
/// of the VM's physical address space) without having to allocate an
/// enormous amount of virtual address space.
///
/// Each region will be `region_size` bytes and will start immediately after
/// the last one. This must be a power of two, be at least a page in size,
/// and cannot fill the full 64-bit address space.
///
/// `imps` must be a list of [`GuestMemoryAccess`] implementations, one for
/// each region. Use `None` if the corresponding region is empty.
///
/// A region's mapping cannot fully fill the region. This is necessary to
/// avoid callers expecting to be able to access a memory range that spans
/// two regions.
pub fn new_multi_region(
debug_name: impl Into<Arc<str>>,
region_size: u64,
mut imps: Vec<Option<impl GuestMemoryAccess>>,
) -> Result<Self, MultiRegionError> {
// Install signal handlers on unix.
sparse_mmap::initialize_try_copy();
if !region_size.is_power_of_two() {
return Err(MultiRegionError::NotPowerOfTwo(region_size));
}
if region_size < PAGE_SIZE64 {
return Err(MultiRegionError::RegionSizeTooSmall(region_size));
}
let region_bits = region_size.trailing_zeros();
let max_region_count = 1 << (63 - region_bits);
let region_count = imps.len().next_power_of_two();
if region_count > max_region_count {
return Err(MultiRegionError::TooManyRegions {
region_count,
max_region_count,
region_size,
});
}
let valid_bits = region_bits + region_count.trailing_zeros();
assert!(valid_bits < 64);
let invalid_mask = !0 << valid_bits;
let mut regions = vec![MemoryRegion::default(); region_count];
for (imp, region) in imps.iter().zip(&mut regions) {
let Some(imp) = imp else { continue };
let backing_size = imp.max_address();
if backing_size > region_size {
return Err(MultiRegionError::BackingTooLarge {
backing_size,
region_size,
});
}
*region = MemoryRegion::new(imp);
}
let region_def = RegionDefinition {
invalid_mask,
region_mask: region_size - 1,
region_bits,
};
imps.resize_with(region_count, || None);
let imp = MultiRegionGuestMemoryAccess { imps, region_def };
let inner = GuestMemoryInner {
debug_name: debug_name.into(),
region_def,
regions,
imp,
};
Ok(Self {
inner: Arc::new(inner),
})
}
/// Allocates a guest memory object on the heap with the given size in
/// bytes.
///
/// `size` will be rounded up to the page size. The backing buffer will be
/// page aligned.
///
/// The debug name in errors will be "heap". If you want to provide a
/// different debug name, manually use `GuestMemory::new` with
/// [`AlignedHeapMemory`].
pub fn allocate(size: usize) -> Self {
GuestMemory::new("heap", AlignedHeapMemory::new(size))
}
/// Returns an empty guest memory, which fails every operation.
pub fn empty() -> Self {
GuestMemory::new("empty", Empty)
}
fn wrap_err(
&self,
gpa_len: Option<(u64, u64)>,
op: GuestMemoryOperation,
err: GuestMemoryBackingError,
) -> GuestMemoryError {
let range = gpa_len.map(|(gpa, len)| (gpa..gpa.wrapping_add(len)));
GuestMemoryError::new(&self.inner.debug_name, range, op, err)
}
fn with_op<T>(
&self,
gpa_len: Option<(u64, u64)>,
op: GuestMemoryOperation,
f: impl FnOnce() -> Result<T, GuestMemoryBackingError>,
) -> Result<T, GuestMemoryError> {
f().map_err(|err| self.wrap_err(gpa_len, op, err))
}
// Creates a smaller view into guest memory, constraining accesses within the new boundaries. For smaller ranges,
// some memory implementations (e.g. HDV) may choose to lock the pages into memory for faster access. Locking
// random guest memory may cause issues, so only opt in to this behavior when the range can be considered "owned"
// by the caller.
pub fn subrange(
&self,
offset: u64,
len: u64,
allow_preemptive_locking: bool,
) -> Result<GuestMemory, GuestMemoryError> {
self.with_op(Some((offset, len)), GuestMemoryOperation::Subrange, || {
if let Some(guest_memory) =
self.inner
.imp
.subrange(offset, len, allow_preemptive_locking)?
{
Ok(guest_memory)
} else {
create_memory_subrange(self.inner.clone(), offset, len, allow_preemptive_locking)
}
})
}
/// Returns the mapping for all of guest memory.
///
/// Returns `None` if there is more than one region or if the memory is not
/// mapped.
pub fn full_mapping(&self) -> Option<(*mut u8, usize)> {
if let [region] = self.inner.regions.as_slice() {
if region.bitmaps.is_some() {
return None;
}
region
.mapping
.map(|SendPtrU8(ptr)| (ptr.as_ptr(), region.len as usize))
} else {
None
}
}
/// Gets the IO address for DMAing to `gpa` from a user-mode driver not
/// going through an IOMMU.
pub fn iova(&self, gpa: u64) -> Option<u64> {
let (region, offset, _) = self.inner.region(gpa, 1).ok()?;
Some(region.base_iova? + offset)
}
/// Gets a pointer to the VA range for `gpa..gpa+len`.
///
/// Returns `Ok(None)` if there is no mapping. Returns `Err(_)` if the
/// memory is out of range.
fn mapping_range(
&self,
access_type: AccessType,
gpa: u64,
len: usize,
) -> Result<Option<*mut u8>, GuestMemoryBackingError> {
let (region, offset, _) = self.inner.region(gpa, len as u64)?;
if let Some(SendPtrU8(ptr)) = region.mapping {
loop {
// SAFETY: offset + len is checked by `region()` to be inside the VA range.
let fault_offset = unsafe {
match region.check_access(access_type, offset, len as u64) {
Ok(()) => return Ok(Some(ptr.as_ptr().add(offset as usize))),
Err(n) => n,
}
};
// Resolve the fault and try again.
match self.inner.imp.page_fault(
gpa + fault_offset,
len - fault_offset as usize,
access_type == AccessType::Write,
true,
) {
PageFaultAction::Fail(err) => {
return Err(GuestMemoryBackingError::new(gpa + fault_offset, err))
}
PageFaultAction::Retry => {}
PageFaultAction::Fallback => break,
}
}
}
Ok(None)
}
/// Runs `f` with a pointer to the mapped memory. If `f` fails, tries to
/// resolve the fault (failing on error), then loops.
///
/// If there is no mapping for the memory, or if the fault handler requests
/// it, call `fallback` instead. `fallback` will not be called unless `gpa`
/// and `len` are in range.
fn run_on_mapping<T, P>(
&self,
access_type: AccessType,
gpa: u64,
len: usize,
mut param: P,
mut f: impl FnMut(&mut P, *mut u8) -> Result<T, sparse_mmap::MemoryError>,
fallback: impl FnOnce(&mut P) -> Result<T, GuestMemoryBackingError>,
) -> Result<T, GuestMemoryBackingError> {
let Some(mapping) = self.mapping_range(access_type, gpa, len)? else {
return fallback(&mut param);
};
// Try until the fault fails to resolve.
loop {
match f(&mut param, mapping) {
Ok(t) => return Ok(t),
Err(fault) => {
match self.inner.imp.page_fault(
gpa + fault.offset() as u64,
len - fault.offset(),
access_type == AccessType::Write,
false,
) {
PageFaultAction::Fail(err) => {
return Err(GuestMemoryBackingError::new(
gpa + fault.offset() as u64,
err,
))
}
PageFaultAction::Retry => {}
PageFaultAction::Fallback => return fallback(&mut param),
}
}
}
}
}
unsafe fn write_ptr(
&self,
gpa: u64,
src: *const u8,
len: usize,
) -> Result<(), GuestMemoryBackingError> {
if len == 0 {
return Ok(());
}
self.run_on_mapping(
AccessType::Write,
gpa,
len,
(),
|(), dest| {
// SAFETY: dest..dest+len is guaranteed to point to a reserved VA
// range, and src..src+len is guaranteed by the caller to be a valid
// buffer for reads.
unsafe { sparse_mmap::try_copy(src, dest, len) }
},
|()| {
// SAFETY: src..src+len is guaranteed by the caller to point to a valid
// buffer for reads.
unsafe { self.inner.imp.write_fallback(gpa, src, len) }
},
)
}
/// Writes `src` into guest memory at address `gpa`.
pub fn write_at(&self, gpa: u64, src: &[u8]) -> Result<(), GuestMemoryError> {
self.with_op(
Some((gpa, src.len() as u64)),
GuestMemoryOperation::Write,
|| self.write_at_inner(gpa, src),
)
}
fn write_at_inner(&self, gpa: u64, src: &[u8]) -> Result<(), GuestMemoryBackingError> {
// SAFETY: `src` is a valid buffer for reads.
unsafe { self.write_ptr(gpa, src.as_ptr(), src.len()) }
}
/// Writes `src` into guest memory at address `gpa`.
pub fn write_from_atomic(&self, gpa: u64, src: &[AtomicU8]) -> Result<(), GuestMemoryError> {
self.with_op(
Some((gpa, src.len() as u64)),
GuestMemoryOperation::Write,
|| {
// SAFETY: `src` is a valid buffer for reads.
unsafe { self.write_ptr(gpa, src.as_ptr().cast(), src.len()) }
},
)
}
/// Writes `len` bytes of `val` into guest memory at address `gpa`.
pub fn fill_at(&self, gpa: u64, val: u8, len: usize) -> Result<(), GuestMemoryError> {
self.with_op(Some((gpa, len as u64)), GuestMemoryOperation::Fill, || {
self.fill_at_inner(gpa, val, len)
})
}
fn fill_at_inner(&self, gpa: u64, val: u8, len: usize) -> Result<(), GuestMemoryBackingError> {
if len == 0 {
return Ok(());
}
self.run_on_mapping(
AccessType::Write,
gpa,
len,
(),
|(), dest| {
// SAFETY: dest..dest+len is guaranteed to point to a reserved VA range.
unsafe { sparse_mmap::try_write_bytes(dest, val, len) }
},
|()| self.inner.imp.fill_fallback(gpa, val, len),
)
}
/// Reads from guest memory into `dest..dest+len`.
///
/// # Safety
/// The caller must ensure dest..dest+len is a valid buffer for writes.
unsafe fn read_ptr(
&self,
gpa: u64,
dest: *mut u8,
len: usize,
) -> Result<(), GuestMemoryBackingError> {
if len == 0 {
return Ok(());
}
self.run_on_mapping(
AccessType::Read,
gpa,
len,
(),
|(), src| {
// SAFETY: src..src+len is guaranteed to point to a reserved VA
// range, and dest..dest+len is guaranteed by the caller to be a
// valid buffer for writes.
unsafe { sparse_mmap::try_copy(src, dest, len) }
},
|()| {
// SAFETY: dest..dest+len is guaranteed by the caller to point to a
// valid buffer for writes.
unsafe { self.inner.imp.read_fallback(gpa, dest, len) }
},
)
}
fn read_at_inner(&self, gpa: u64, dest: &mut [u8]) -> Result<(), GuestMemoryBackingError> {
// SAFETY: `dest` is a valid buffer for writes.
unsafe { self.read_ptr(gpa, dest.as_mut_ptr(), dest.len()) }
}
/// Reads from guest memory address `gpa` into `dest`.
pub fn read_at(&self, gpa: u64, dest: &mut [u8]) -> Result<(), GuestMemoryError> {
self.with_op(
Some((gpa, dest.len() as u64)),
GuestMemoryOperation::Read,
|| self.read_at_inner(gpa, dest),
)
}
/// Reads from guest memory address `gpa` into `dest`.
pub fn read_to_atomic(&self, gpa: u64, dest: &[AtomicU8]) -> Result<(), GuestMemoryError> {
self.with_op(
Some((gpa, dest.len() as u64)),
GuestMemoryOperation::Read,
// SAFETY: `dest` is a valid buffer for writes.
|| unsafe { self.read_ptr(gpa, dest.as_ptr() as *mut u8, dest.len()) },
)
}
/// Writes an object to guest memory at address `gpa`.
///
/// If the object is 1, 2, 4, or 8 bytes and the address is naturally
/// aligned, then the write will be performed atomically. Here, this means
/// that concurrent readers (via `read_plain`) cannot observe a torn write
/// but will observe either the old or new value.
///
/// The memory ordering of the write is unspecified.
///
/// FUTURE: once we are on Rust 1.79, add a method specifically for atomic
/// accesses that const asserts that the size is appropriate.
pub fn write_plain<T: AsBytes>(&self, gpa: u64, b: &T) -> Result<(), GuestMemoryError> {
// Note that this is const, so the match below will compile out.
let len = size_of::<T>();
self.with_op(Some((gpa, len as u64)), GuestMemoryOperation::Write, || {
self.run_on_mapping(
AccessType::Write,
gpa,
len,
(),
|(), dest| {
match len {
1 | 2 | 4 | 8 => {
// SAFETY: dest..dest+len is guaranteed to point to
// a reserved VA range.
unsafe { sparse_mmap::try_write_volatile(dest.cast(), b) }
}
_ => {
// SAFETY: dest..dest+len is guaranteed to point to
// a reserved VA range.
unsafe { sparse_mmap::try_copy(b.as_bytes().as_ptr(), dest, len) }
}
}
},
|()| {
// SAFETY: b is a valid buffer for reads.
unsafe {
self.inner
.imp
.write_fallback(gpa, b.as_bytes().as_ptr(), len)
}
},
)
})
}
/// Attempts a sequentially-consistent compare exchange of the value at `gpa`.
pub fn compare_exchange<T: AsBytes + FromBytes + Copy>(
&self,
gpa: u64,
current: T,
new: T,
) -> Result<Result<T, T>, GuestMemoryError> {
let len = size_of_val(&new);
self.with_op(
Some((gpa, len as u64)),
GuestMemoryOperation::CompareExchange,
|| {
// Assume that if write is allowed, then read is allowed.
self.run_on_mapping(
AccessType::Write,
gpa,
len,
(),
|(), dest| {
// SAFETY: dest..dest+len is guaranteed by the caller to be a valid
// buffer for writes.
unsafe { sparse_mmap::try_compare_exchange(dest.cast(), current, new) }
},
|()| {
let mut current = current;
let success = self.inner.imp.compare_exchange_fallback(
gpa,
current.as_bytes_mut(),
new.as_bytes(),
)?;
Ok(if success { Ok(new) } else { Err(current) })
},
)
},
)
}
/// Attempts a sequentially-consistent compare exchange of the value at `gpa`.
pub fn compare_exchange_bytes<T: AsBytes + FromBytes + ?Sized>(
&self,
gpa: u64,
current: &mut T,
new: &T,
) -> Result<bool, GuestMemoryError> {
let len = size_of_val(new);
assert_eq!(size_of_val(current), len);
self.with_op(
Some((gpa, len as u64)),
GuestMemoryOperation::CompareExchange,
|| {
// Assume that if write is allowed, then read is allowed.
self.run_on_mapping(
AccessType::Write,
gpa,
len,
current,
|current, dest| {
// SAFETY: dest..dest+len is guaranteed by the caller to be a valid
// buffer for writes.
unsafe { sparse_mmap::try_compare_exchange_ref(dest, *current, new) }
},
|current| {
let success = self.inner.imp.compare_exchange_fallback(
gpa,
current.as_bytes_mut(),
new.as_bytes(),
)?;
Ok(success)
},
)
},
)
}
/// Reads an object from guest memory at address `gpa`.
///
/// If the object is 1, 2, 4, or 8 bytes and the address is naturally
/// aligned, then the read will be performed atomically. Here, this means
/// that when there is a concurrent writer, callers will observe either the
/// old or new value, but not a torn read.
///
/// The memory ordering of the read is unspecified.
///
/// FUTURE: once we are on Rust 1.79, add a method specifically for atomic
/// accesses that const asserts that the size is appropriate.
pub fn read_plain<T: FromBytes>(&self, gpa: u64) -> Result<T, GuestMemoryError> {
// Note that this is const, so the match below will compile out.
let len = size_of::<T>();
self.with_op(Some((gpa, len as u64)), GuestMemoryOperation::Read, || {
self.run_on_mapping(
AccessType::Read,
gpa,
len,
(),
|(), src| {
match len {
1 | 2 | 4 | 8 => {
// SAFETY: src..src+len is guaranteed to point to a reserved VA
// range.
unsafe { sparse_mmap::try_read_volatile(src.cast::<T>()) }
}
_ => {
let mut obj = std::mem::MaybeUninit::<T>::zeroed();
// SAFETY: src..src+len is guaranteed to point to a reserved VA
// range.
unsafe { sparse_mmap::try_copy(src, obj.as_mut_ptr().cast(), len)? };
// SAFETY: `obj` was fully initialized by `try_copy`.
Ok(unsafe { obj.assume_init() })
}
}
},
|()| {
let mut obj = std::mem::MaybeUninit::<T>::zeroed();
// SAFETY: dest..dest+len is guaranteed by the caller to point to a
// valid buffer for writes.
unsafe {
self.inner
.imp
.read_fallback(gpa, obj.as_mut_ptr().cast(), len)?;
}
// SAFETY: `obj` was fully initialized by `read_fallback`.
Ok(unsafe { obj.assume_init() })
},
)
})
}
fn probe_page_for_lock(
&self,
with_kernel_access: bool,
gpa: u64,
) -> Result<*const AtomicU8, GuestMemoryBackingError> {
let (region, offset, _) = self.inner.region(gpa, 1)?;
let Some(SendPtrU8(ptr)) = region.mapping else {
return Err(GuestMemoryBackingError::new(gpa, NotLockable));
};
// Ensure the virtual address can be exposed.
if with_kernel_access {
self.inner.imp.expose_va(gpa, 1)?;
}
let mut b = [0];
// FUTURE: check the correct bitmap for the access type, which needs to
// be passed in.
self.read_at_inner(gpa, &mut b)?;
// SAFETY: the read_at call includes a check that ensures that
// `gpa` is in the VA range.
let page = unsafe { ptr.as_ptr().add(offset as usize) };
Ok(page.cast())
}
pub fn lock_gpns(
&self,
with_kernel_access: bool,
gpns: &[u64],
) -> Result<LockedPages, GuestMemoryError> {
self.with_op(None, GuestMemoryOperation::Lock, || {
let mut pages = Vec::with_capacity(gpns.len());
for &gpn in gpns {
let gpa = gpn_to_gpa(gpn).map_err(GuestMemoryBackingError::gpn)?;
let page = self.probe_page_for_lock(with_kernel_access, gpa)?;
pages.push(PagePtr(page));
}
Ok(LockedPages {
pages: pages.into_boxed_slice(),
_mem: self.inner.clone(),
})
})
}
pub fn probe_gpns(&self, gpns: &[u64]) -> Result<(), GuestMemoryError> {
self.with_op(None, GuestMemoryOperation::Probe, || {
for &gpn in gpns {
let mut b = [0];
self.read_at_inner(
gpn_to_gpa(gpn).map_err(GuestMemoryBackingError::gpn)?,
&mut b,
)?;
}
Ok(())
})
}
/// Check if a given GPA is readable or not.
pub fn check_gpa_readable(&self, gpa: u64) -> bool {
let mut b = [0];
self.read_at_inner(gpa, &mut b).is_ok()
}
/// Gets a slice of guest memory assuming the memory was already locked via
/// [`GuestMemory::lock_gpns`].
///
/// This is dangerous--if the pages have not been locked, then it could
/// cause an access violation or guest memory corruption.
///
/// Note that this is not `unsafe` since this cannot cause memory corruption
/// in this process. Even if there is an access violation, the underlying VA
/// space is known to be reserved.
///
/// Panics if the requested buffer is out of range.
fn dangerous_access_pre_locked_memory(&self, gpa: u64, len: usize) -> &[AtomicU8] {
let addr = self
.mapping_range(AccessType::Write, gpa, len)
.unwrap()
.unwrap();
// SAFETY: addr..addr+len is checked above to be a valid VA range. It's
// possible some of the pages aren't mapped and will cause AVs at
// runtime when accessed, but, as discussed above, at a language level
// this cannot cause any safety issues.
unsafe { std::slice::from_raw_parts(addr.cast(), len) }
}
fn op_range<F: FnMut(u64, Range<usize>) -> Result<(), GuestMemoryBackingError>>(
&self,
op: GuestMemoryOperation,
range: &PagedRange<'_>,
mut f: F,
) -> Result<(), GuestMemoryError> {
self.with_op(None, op, || {
let gpns = range.gpns();
let offset = range.offset();
// Perform the operation in three phases: the first page (if it is not a
// full page), the full pages, and the last page (if it is not a full
// page).
let mut byte_index = 0;
let mut len = range.len();
let mut page = 0;
if offset % PAGE_SIZE != 0 {
let head_len = std::cmp::min(len, PAGE_SIZE - (offset % PAGE_SIZE));
let addr = gpn_to_gpa(gpns[page]).map_err(GuestMemoryBackingError::gpn)?
+ offset as u64 % PAGE_SIZE64;
f(addr, byte_index..byte_index + head_len)?;
byte_index += head_len;
len -= head_len;
page += 1;
}
while len >= PAGE_SIZE {
f(
gpn_to_gpa(gpns[page]).map_err(GuestMemoryBackingError::gpn)?,
byte_index..byte_index + PAGE_SIZE,
)?;
byte_index += PAGE_SIZE;
len -= PAGE_SIZE;
page += 1;
}
if len > 0 {
f(
gpn_to_gpa(gpns[page]).map_err(GuestMemoryBackingError::gpn)?,
byte_index..byte_index + len,
)?;
}
Ok(())
})
}
pub fn write_range(&self, range: &PagedRange<'_>, data: &[u8]) -> Result<(), GuestMemoryError> {
assert!(data.len() == range.len());
self.op_range(GuestMemoryOperation::Write, range, move |addr, r| {
self.write_at_inner(addr, &data[r])
})
}
pub fn zero_range(&self, range: &PagedRange<'_>) -> Result<(), GuestMemoryError> {
self.op_range(GuestMemoryOperation::Fill, range, move |addr, r| {
self.fill_at_inner(addr, 0, r.len())
})
}
pub fn read_range(
&self,
range: &PagedRange<'_>,
data: &mut [u8],
) -> Result<(), GuestMemoryError> {
assert!(data.len() == range.len());
self.op_range(GuestMemoryOperation::Read, range, move |addr, r| {
self.read_at_inner(addr, &mut data[r])
})
}
pub fn write_range_from_atomic(
&self,
range: &PagedRange<'_>,
data: &[AtomicU8],
) -> Result<(), GuestMemoryError> {
assert!(data.len() == range.len());
self.op_range(GuestMemoryOperation::Write, range, move |addr, r| {
let src = &data[r];
// SAFETY: `src` is a valid buffer for reads.
unsafe { self.write_ptr(addr, src.as_ptr().cast(), src.len()) }
})
}
pub fn read_range_to_atomic(
&self,
range: &PagedRange<'_>,
data: &[AtomicU8],
) -> Result<(), GuestMemoryError> {
assert!(data.len() == range.len());
self.op_range(GuestMemoryOperation::Read, range, move |addr, r| {
let dest = &data[r];
// SAFETY: `dest` is a valid buffer for writes.
unsafe { self.read_ptr(addr, dest.as_ptr().cast_mut().cast(), dest.len()) }
})
}
/// Locks the guest pages spanned by the specified `PagedRange` for the `'static` lifetime.
///
/// # Arguments
/// * 'paged_range' - The guest memory range to lock.
/// * 'locked_range' - Receives a list of VA ranges to which each contiguous physical sub-range in `paged_range`
/// has been mapped. Must be initially empty.
pub fn lock_range<T: LockedRange>(
&self,
paged_range: PagedRange<'_>,
mut locked_range: T,
) -> Result<LockedRangeImpl<T>, GuestMemoryError> {
self.with_op(None, GuestMemoryOperation::Lock, || {
let gpns = paged_range.gpns();
for &gpn in gpns {
let gpa = gpn_to_gpa(gpn).map_err(GuestMemoryBackingError::gpn)?;
self.probe_page_for_lock(true, gpa)?;
}
for range in paged_range.ranges() {
let range = range.map_err(GuestMemoryBackingError::gpn)?;
locked_range.push_sub_range(
self.dangerous_access_pre_locked_memory(range.start, range.len() as usize),
);
}
Ok(LockedRangeImpl {
_mem: self.inner.clone(),
inner: locked_range,
})
})
}
}
#[derive(Debug, Error)]
#[error("invalid guest page number {0:#x}")]
pub struct InvalidGpn(u64);
fn gpn_to_gpa(gpn: u64) -> Result<u64, InvalidGpn> {
gpn.checked_mul(PAGE_SIZE64).ok_or(InvalidGpn(gpn))
}
#[derive(Debug, Copy, Clone, Default)]
struct RegionDefinition {
invalid_mask: u64,
region_mask: u64,
region_bits: u32,
}
impl RegionDefinition {
fn region(&self, gpa: u64, len: u64) -> Result<(usize, u64), GuestMemoryBackingError> {
if (gpa | len) & self.invalid_mask != 0 {
return Err(GuestMemoryBackingError::new(gpa, OutOfRange));
}
let offset = gpa & self.region_mask;
if offset.wrapping_add(len) & !self.region_mask != 0 {
return Err(GuestMemoryBackingError::new(gpa, OutOfRange));
}
let index = (gpa >> self.region_bits) as usize;
Ok((index, offset))
}
}
impl GuestMemoryInner {
fn region(
&self,
gpa: u64,
len: u64,
) -> Result<(&MemoryRegion, u64, usize), GuestMemoryBackingError> {
let (index, offset) = self.region_def.region(gpa, len)?;
let region = &self.regions[index];
if offset + len > region.len {
return Err(GuestMemoryBackingError::new(gpa, OutOfRange));
}
Ok((&self.regions[index], offset, index))
}
}
#[derive(Clone)]
pub struct LockedPages {
pages: Box<[PagePtr]>,
// maintain a reference to the backing memory
_mem: Arc<GuestMemoryInner>,
}
impl Debug for LockedPages {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_struct("LockedPages")
.field("page_count", &self.pages.len())
.finish()
}
}
#[derive(Copy, Clone, Debug)]
// Field is read via slice transmute and pointer casts, not actually dead.
struct PagePtr(#[allow(dead_code)] *const AtomicU8);
// SAFETY: PagePtr is just a pointer with no methods and has no inherent safety
// constraints.
unsafe impl Send for PagePtr {}
// SAFETY: see above comment
unsafe impl Sync for PagePtr {}
pub type Page = [AtomicU8; PAGE_SIZE];
impl LockedPages {
#[inline]
pub fn pages(&self) -> &[&Page] {
// SAFETY: PagePtr is just a pointer to a Page. The pages are kept alive by
// the reference in _mem, and the lifetimes here ensure the LockedPages outlives
// the slice.
unsafe { std::slice::from_raw_parts(self.pages.as_ptr().cast::<&Page>(), self.pages.len()) }
}
}
impl<'a> AsRef<[&'a Page]> for &'a LockedPages {
fn as_ref(&self) -> &[&'a Page] {
self.pages()
}
}
/// Represents a range of locked guest pages as an ordered list of the VA sub-ranges
/// to which the guest pages are mapped.
/// The range may only partially span the first and last page and must fully span all
/// intermediate pages.
pub trait LockedRange {
/// Adds a sub-range to this range.
fn push_sub_range(&mut self, sub_range: &[AtomicU8]);
/// Removes and returns the last sub range.
fn pop_sub_range(&mut self) -> Option<(*const AtomicU8, usize)>;
}
pub struct LockedRangeImpl<T: LockedRange> {
_mem: Arc<GuestMemoryInner>,
inner: T,
}
impl<T: LockedRange> LockedRangeImpl<T> {
pub fn get(&self) -> &T {
&self.inner
}
}
impl<T: LockedRange> Drop for LockedRangeImpl<T> {
fn drop(&mut self) {
// FUTURE: Remove and unlock all sub ranges. This is currently
// not necessary yet as only fully mapped VMs are supported.
// while let Some(sub_range) = self.inner.pop_sub_range() {
// call self._mem to unlock the sub-range, individually or in batches
// }
}
}
#[derive(Debug, Error)]
pub enum AccessError {
#[error("memory access error")]
Memory(#[from] GuestMemoryError),
#[error("out of range: {0:#x} < {1:#x}")]
OutOfRange(usize, usize),
#[error("write attempted to read-only memory")]
ReadOnly,
}
pub trait MemoryRead {
fn read(&mut self, data: &mut [u8]) -> Result<&mut Self, AccessError>;
fn skip(&mut self, len: usize) -> Result<&mut Self, AccessError>;
fn len(&self) -> usize;
fn read_plain<T: AsBytes + FromBytes>(&mut self) -> Result<T, AccessError> {
let mut value: T = FromZeroes::new_zeroed();
self.read(value.as_bytes_mut())?;
Ok(value)
}
fn read_n<T: AsBytes + FromBytes + Copy>(&mut self, len: usize) -> Result<Vec<T>, AccessError> {
let mut value = vec![FromZeroes::new_zeroed(); len];
self.read(value.as_bytes_mut())?;
Ok(value)
}
fn read_all(&mut self) -> Result<Vec<u8>, AccessError> {
let mut value = vec![0; self.len()];
self.read(&mut value)?;
Ok(value)
}
fn limit(self, len: usize) -> Limit<Self>
where
Self: Sized,
{
let len = len.min(self.len());
Limit { inner: self, len }
}
}
pub trait MemoryWrite {
fn write(&mut self, data: &[u8]) -> Result<(), AccessError>;
fn zero(&mut self, len: usize) -> Result<(), AccessError>;
fn len(&self) -> usize;
fn limit(self, len: usize) -> Limit<Self>
where
Self: Sized,
{
let len = len.min(self.len());
Limit { inner: self, len }
}
}
impl MemoryRead for &'_ [u8] {
fn read(&mut self, data: &mut [u8]) -> Result<&mut Self, AccessError> {
if self.len() < data.len() {
return Err(AccessError::OutOfRange(self.len(), data.len()));
}
let (source, rest) = self.split_at(data.len());
data.copy_from_slice(source);
*self = rest;
Ok(self)
}
fn skip(&mut self, len: usize) -> Result<&mut Self, AccessError> {
if self.len() < len {
return Err(AccessError::OutOfRange(self.len(), len));
}
*self = &self[len..];
Ok(self)
}
fn len(&self) -> usize {
<[u8]>::len(self)
}
}
impl MemoryWrite for &mut [u8] {
fn write(&mut self, data: &[u8]) -> Result<(), AccessError> {
if self.len() < data.len() {
return Err(AccessError::OutOfRange(self.len(), data.len()));
}
let (dest, rest) = std::mem::take(self).split_at_mut(data.len());
dest.copy_from_slice(data);
*self = rest;
Ok(())
}
fn zero(&mut self, len: usize) -> Result<(), AccessError> {
if self.len() < len {
return Err(AccessError::OutOfRange(self.len(), len));
}
let (dest, rest) = std::mem::take(self).split_at_mut(len);
for b in dest.iter_mut() {
*b = 0
}
*self = rest;
Ok(())
}
fn len(&self) -> usize {
<[u8]>::len(self)
}
}
#[derive(Debug, Clone)]
pub struct Limit<T> {
inner: T,
len: usize,
}
impl<T: MemoryRead> MemoryRead for Limit<T> {
fn read(&mut self, data: &mut [u8]) -> Result<&mut Self, AccessError> {
let len = data.len();
if len > self.len {
return Err(AccessError::OutOfRange(self.len, len));
}
self.inner.read(data)?;
self.len -= len;
Ok(self)
}
fn skip(&mut self, len: usize) -> Result<&mut Self, AccessError> {
if len > self.len {
return Err(AccessError::OutOfRange(self.len, len));
}
self.inner.skip(len)?;
self.len -= len;
Ok(self)
}
fn len(&self) -> usize {
self.len
}
}
impl<T: MemoryWrite> MemoryWrite for Limit<T> {
fn write(&mut self, data: &[u8]) -> Result<(), AccessError> {
let len = data.len();
if len > self.len {
return Err(AccessError::OutOfRange(self.len, len));
}
self.inner.write(data)?;
self.len -= len;
Ok(())
}
fn zero(&mut self, len: usize) -> Result<(), AccessError> {
if len > self.len {
return Err(AccessError::OutOfRange(self.len, len));
}
self.inner.zero(len)?;
self.len -= len;
Ok(())
}
fn len(&self) -> usize {
self.len
}
}
/// Trait implemented to allow mapping and unmapping a region of memory at
/// a particular guest address.
pub trait MappableGuestMemory: Send + Sync {
/// Maps the memory into the guest.
///
/// `writable` specifies whether the guest can write to the memory region.
/// If a guest tries to write to a non-writable region, the virtual
/// processor will exit for MMIO handling.
fn map_to_guest(&mut self, gpa: u64, writable: bool) -> io::Result<()>;
fn unmap_from_guest(&mut self);
}
/// Trait implemented for a region of memory that can have memory mapped into
/// it.
pub trait MappedMemoryRegion: Send + Sync {
/// Maps an object at `offset` in the region.
///
/// Behaves like mmap--overwrites and splits existing mappings.
fn map(
&self,
offset: usize,
section: &dyn AsMappableRef,
file_offset: u64,
len: usize,
writable: bool,
) -> io::Result<()>;
/// Unmaps any mappings in the specified range within the region.
fn unmap(&self, offset: usize, len: usize) -> io::Result<()>;
}
/// Trait implemented to allow the creation of memory regions.
pub trait MemoryMapper: Send + Sync {
/// Creates a new memory region that can later be mapped into the guest.
///
/// Returns both an interface for mapping/unmapping the region and for
/// adding internal mappings.
fn new_region(
&self,
len: usize,
debug_name: String,
) -> io::Result<(Box<dyn MappableGuestMemory>, Arc<dyn MappedMemoryRegion>)>;
}
/// Doorbell provides a mechanism to register for notifications on writes to specific addresses in guest memory.
pub trait DoorbellRegistration: Send + Sync {
/// Register a doorbell event.
fn register_doorbell(
&self,
guest_address: u64,
value: Option<u64>,
length: Option<u32>,
event: &Event,
) -> io::Result<Box<dyn Send + Sync>>;
}
/// Trait to map a ROM at one or more locations in guest memory.
pub trait MapRom: Send + Sync {
/// Maps the specified portion of the ROM into guest memory at `gpa`.
///
/// The returned object will implicitly unmap the ROM when dropped.
fn map_rom(&self, gpa: u64, offset: u64, len: u64) -> io::Result<Box<dyn UnmapRom>>;
/// Returns the length of the ROM in bytes.
fn len(&self) -> u64;
}
/// Trait to unmap a ROM from guest memory.
pub trait UnmapRom: Send + Sync {
/// Unmaps the ROM from guest memory.
fn unmap_rom(self);
}
#[cfg(test)]
#[allow(clippy::undocumented_unsafe_blocks)]
mod tests {
use crate::BitmapInfo;
use crate::GuestMemory;
use crate::PageFaultAction;
use crate::PAGE_SIZE64;
use sparse_mmap::SparseMapping;
use std::ptr::NonNull;
use std::sync::Arc;
use thiserror::Error;
/// An implementation of a GuestMemoryAccess trait that expects all of
/// guest memory to be mapped at a given base, with mmap or the Windows
/// equivalent. Pages that are not backed by RAM will return failure
/// when attempting to access them.
pub struct GuestMemoryMapping {
mapping: SparseMapping,
bitmap: Option<Vec<u8>>,
}
unsafe impl crate::GuestMemoryAccess for GuestMemoryMapping {
fn mapping(&self) -> Option<NonNull<u8>> {
NonNull::new(self.mapping.as_ptr().cast())
}
fn max_address(&self) -> u64 {
self.mapping.len() as u64
}
fn access_bitmap(&self) -> Option<BitmapInfo> {
self.bitmap.as_ref().map(|bm| BitmapInfo {
read_bitmap: NonNull::new(bm.as_ptr().cast_mut()).unwrap(),
write_bitmap: NonNull::new(bm.as_ptr().cast_mut()).unwrap(),
execute_bitmap: NonNull::new(bm.as_ptr().cast_mut()).unwrap(),
bit_offset: 0,
})
}
}
const PAGE_SIZE: usize = 4096;
const SIZE_1MB: usize = 1048576;
/// Create a test guest layout:
/// 0 -> 1MB RAM
/// 1MB -> 2MB empty
/// 2MB -> 3MB RAM
/// 3MB -> 3MB + 4K empty
/// 3MB + 4K -> 4MB RAM
fn create_test_mapping() -> GuestMemoryMapping {
let mapping = SparseMapping::new(SIZE_1MB * 4).unwrap();
mapping.alloc(0, SIZE_1MB).unwrap();
mapping.alloc(2 * SIZE_1MB, SIZE_1MB).unwrap();
mapping
.alloc(3 * SIZE_1MB + PAGE_SIZE, SIZE_1MB - PAGE_SIZE)
.unwrap();
GuestMemoryMapping {
mapping,
bitmap: None,
}
}
#[test]
fn test_basic_read_write() {
let mapping = create_test_mapping();
let gm = GuestMemory::new("test", mapping);
// Test reading at 0.
let addr = 0;
let result = gm.read_plain::<u8>(addr);
assert_eq!(result.unwrap(), 0);
// Test read/write to first page
let write_buffer = [1, 2, 3, 4, 5];
let mut read_buffer = [0; 5];
gm.write_at(0, &write_buffer).unwrap();
gm.read_at(0, &mut read_buffer).unwrap();
assert_eq!(write_buffer, read_buffer);
assert_eq!(gm.read_plain::<u8>(0).unwrap(), 1);
assert_eq!(gm.read_plain::<u8>(1).unwrap(), 2);
assert_eq!(gm.read_plain::<u8>(2).unwrap(), 3);
assert_eq!(gm.read_plain::<u8>(3).unwrap(), 4);
assert_eq!(gm.read_plain::<u8>(4).unwrap(), 5);
// Test read/write to page at 2MB
let addr = 2 * SIZE_1MB as u64;
let write_buffer: Vec<u8> = (0..PAGE_SIZE).map(|x| x as u8).collect();
let mut read_buffer: Vec<u8> = (0..PAGE_SIZE).map(|_| 0).collect();
gm.write_at(addr, write_buffer.as_slice()).unwrap();
gm.read_at(addr, read_buffer.as_mut_slice()).unwrap();
assert_eq!(write_buffer, read_buffer);
// Test read/write to first 1MB
let write_buffer: Vec<u8> = (0..SIZE_1MB).map(|x| x as u8).collect();
let mut read_buffer: Vec<u8> = (0..SIZE_1MB).map(|_| 0).collect();
gm.write_at(addr, write_buffer.as_slice()).unwrap();
gm.read_at(addr, read_buffer.as_mut_slice()).unwrap();
assert_eq!(write_buffer, read_buffer);
// Test bad read at 1MB
let addr = SIZE_1MB as u64;
let result = gm.read_plain::<u8>(addr);
assert!(result.is_err());
}
#[test]
fn test_multi() {
let len = SIZE_1MB * 4;
let mapping = SparseMapping::new(len).unwrap();
mapping.alloc(0, len).unwrap();
let mapping = Arc::new(GuestMemoryMapping {
mapping,
bitmap: None,
});
let region_len = 1 << 30;
let gm = GuestMemory::new_multi_region(
"test",
region_len,
vec![Some(mapping.clone()), None, Some(mapping.clone())],
)
.unwrap();
let mut b = [0];
let len = len as u64;
gm.read_at(0, &mut b).unwrap();
gm.read_at(len, &mut b).unwrap_err();
gm.read_at(region_len, &mut b).unwrap_err();
gm.read_at(2 * region_len, &mut b).unwrap();
gm.read_at(2 * region_len + len, &mut b).unwrap_err();
gm.read_at(3 * region_len, &mut b).unwrap_err();
}
#[test]
fn test_bitmap() {
let len = PAGE_SIZE * 4;
let mapping = SparseMapping::new(len).unwrap();
mapping.alloc(0, len).unwrap();
let bitmap = vec![0b0101];
let mapping = Arc::new(GuestMemoryMapping {
mapping,
bitmap: Some(bitmap),
});
let gm = GuestMemory::new("test", mapping);
gm.read_plain::<[u8; 1]>(0).unwrap();
gm.read_plain::<[u8; 1]>(PAGE_SIZE64 - 1).unwrap();
gm.read_plain::<[u8; 2]>(PAGE_SIZE64 - 1).unwrap_err();
gm.read_plain::<[u8; 1]>(PAGE_SIZE64).unwrap_err();
gm.read_plain::<[u8; 1]>(PAGE_SIZE64 * 2).unwrap();
gm.read_plain::<[u8; PAGE_SIZE * 2]>(0).unwrap_err();
}
struct FaultingMapping {
mapping: SparseMapping,
}
#[derive(Debug, Error)]
#[error("fault")]
struct Fault;
unsafe impl crate::GuestMemoryAccess for FaultingMapping {
fn mapping(&self) -> Option<NonNull<u8>> {
NonNull::new(self.mapping.as_ptr().cast())
}
fn max_address(&self) -> u64 {
self.mapping.len() as u64
}
fn page_fault(
&self,
address: u64,
_len: usize,
write: bool,
bitmap_failure: bool,
) -> PageFaultAction {
assert!(!bitmap_failure);
let qlen = self.mapping.len() as u64 / 4;
if address < qlen || address >= 3 * qlen {
return PageFaultAction::Fail(Fault.into());
}
let page_address = (address as usize) & !(PAGE_SIZE - 1);
if address >= 2 * qlen {
if write {
return PageFaultAction::Fail(Fault.into());
}
self.mapping.map_zero(page_address, PAGE_SIZE).unwrap();
} else {
self.mapping.alloc(page_address, PAGE_SIZE).unwrap();
}
PageFaultAction::Retry
}
}
impl FaultingMapping {
fn new(len: usize) -> Self {
let mapping = SparseMapping::new(len).unwrap();
FaultingMapping { mapping }
}
}
#[test]
fn test_fault() {
let len = PAGE_SIZE * 4;
let mapping = FaultingMapping::new(len);
let gm = GuestMemory::new("test", mapping);
gm.write_plain::<u8>(0, &0).unwrap_err();
gm.read_plain::<u8>(PAGE_SIZE64 - 1).unwrap_err();
gm.read_plain::<u8>(PAGE_SIZE64).unwrap();
gm.write_plain::<u8>(PAGE_SIZE64, &0).unwrap();
gm.write_plain::<u16>(PAGE_SIZE64 * 3 - 1, &0).unwrap_err();
gm.read_plain::<u16>(PAGE_SIZE64 * 3 - 1).unwrap_err();
gm.read_plain::<u8>(PAGE_SIZE64 * 3 - 1).unwrap();
gm.write_plain::<u8>(PAGE_SIZE64 * 3 - 1, &0).unwrap_err();
}
}