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misc: do not use u64 to represent host pointers

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To ensure that struct sizes are the same on 32-bit and 64-bit, various
kernel APIs use __u64 (Rust u64) to represent userspace pointers.
Userspace is expected to cast pointers to __u64 before passing them to
the kernel, and cast kernel-provided __u64 to a pointer before using
them.  However, various safe APIs in Cloud Hypervisor took
caller-provided u64 values and passed them to syscalls that interpret
them as userspace addresses.  Therefore, passing bad u64 values would
cause memory disclosure or corruption.

Fix the bug by using usize and pointer types as appropriate.  To make
soundness of the code easier to reason about, the PCI code gains a new
MmapRegion abstraction that ensures the validity of pointers.  The rest
of the code already has an MmapRegion abstraction it can use.  To avoid
having to reason about whether something is keeping the MmapRegion
alive, reference counting is added.  MmapRegion cannot hold references
to other objects, so the reference counting cannot introduce cycles.

Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
This commit is contained in:
Demi Marie Obenour
2025-06-13 14:27:00 -04:00
committed by Rob Bradford
parent fdc19ad85e
commit 42522a88c0
17 changed files with 382 additions and 263 deletions
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vmm/src/memory_manager.rs
+63 -31
View File
@@ -8,7 +8,7 @@ use std::collections::BTreeMap;
use std::collections::HashMap;
use std::fs::{File, OpenOptions};
use std::io::{self};
use std::ops::{BitAnd, Deref, Not, Sub};
use std::ops::{BitAnd, Not, Sub};
#[cfg(all(target_arch = "x86_64", feature = "guest_debug"))]
use std::os::fd::AsFd;
use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};
@@ -900,13 +900,12 @@ impl MemoryManager {
for (zone_id, regions) in list {
for (region, virtio_mem) in regions {
// SAFETY: regions only holds valid addresses.
// TODO: encapsulate this unsafety in a small part of the file.
// SAFETY: guaranteed by GuestRegionMmap invariants
let slot = unsafe {
self.create_userspace_mapping(
region.start_addr().raw_value(),
region.len(),
region.as_ptr() as u64,
region.len().try_into().unwrap(),
region.as_ptr(),
self.mergeable,
false,
self.log_dirty,
@@ -962,13 +961,16 @@ impl MemoryManager {
arch::layout::UEFI_START,
)
.unwrap();
const _: () = assert!(core::mem::size_of::<usize>() == core::mem::size_of::<u64>());
// SAFETY: guaranteed by GuestRegionMmap
unsafe {
self.vm
.create_user_memory_region(
uefi_mem_slot,
uefi_region.start_addr().raw_value(),
uefi_region.len(),
uefi_region.as_ptr() as u64,
uefi_region.len() as usize,
uefi_region.as_ptr(),
false,
false,
)
@@ -1364,10 +1366,9 @@ impl MemoryManager {
}
#[allow(clippy::too_many_arguments)]
pub fn create_ram_region(
pub fn create_ram_region_raw(
backing_file: &Option<PathBuf>,
file_offset: u64,
start_addr: GuestAddress,
size: usize,
prefault: bool,
shared: bool,
@@ -1376,7 +1377,7 @@ impl MemoryManager {
host_numa_node: Option<u32>,
existing_memory_file: Option<File>,
thp: bool,
) -> Result<Arc<GuestRegionMmap>, Error> {
) -> Result<MmapRegion<AtomicBitmap>, Error> {
let mut mmap_flags = libc::MAP_NORESERVE;
// The duplication of mmap_flags ORing here is unfortunate but it also makes
@@ -1403,17 +1404,13 @@ impl MemoryManager {
None
};
let region = GuestRegionMmap::new(
MmapRegion::build(fo, size, libc::PROT_READ | libc::PROT_WRITE, mmap_flags)
.map_err(Error::GuestMemoryRegion)?,
start_addr,
)
.map_err(Error::GuestMemory)?;
let region = MmapRegion::build(fo, size, libc::PROT_READ | libc::PROT_WRITE, mmap_flags)
.map_err(Error::GuestMemoryRegion)?;
// Apply NUMA policy if needed.
if let Some(node) = host_numa_node {
let addr = region.deref().as_ptr();
let len = region.deref().size() as u64;
let addr = region.as_ptr();
let len = region.size() as u64;
let mode = MPOL_BIND;
let mut nodemask: Vec<u64> = Vec::new();
let flags = MPOL_MF_STRICT | MPOL_MF_MOVE;
@@ -1498,7 +1495,39 @@ impl MemoryManager {
}
}
Ok(Arc::new(region))
Ok(region)
}
#[allow(clippy::too_many_arguments)]
pub fn create_ram_region(
backing_file: &Option<PathBuf>,
file_offset: u64,
start_addr: GuestAddress,
size: usize,
prefault: bool,
shared: bool,
hugepages: bool,
hugepage_size: Option<u64>,
host_numa_node: Option<u32>,
existing_memory_file: Option<File>,
thp: bool,
) -> Result<Arc<GuestRegionMmap>, Error> {
let r = Self::create_ram_region_raw(
backing_file,
file_offset,
size,
prefault,
shared,
hugepages,
hugepage_size,
host_numa_node,
existing_memory_file,
thp,
)?;
Ok(Arc::new(
GuestRegionMmap::new(r, start_addr).map_err(Error::GuestMemory)?,
))
}
// Duplicate of `memory_zone_get_align_size` that does not require a `zone`
@@ -1612,12 +1641,12 @@ impl MemoryManager {
)?;
// Map it into the guest
// SAFETY: create_ram_region only produces valid mappings.
// SAFETY: guaranteed by GuestMmapRegion invariants
let slot = unsafe {
self.create_userspace_mapping(
region.start_addr().0,
region.len(),
region.as_ptr() as u64,
region.len().try_into().unwrap(),
region.as_ptr(),
self.mergeable,
false,
self.log_dirty,
@@ -1722,8 +1751,8 @@ impl MemoryManager {
pub unsafe fn create_userspace_mapping(
&mut self,
guest_phys_addr: u64,
memory_size: u64,
userspace_addr: u64,
memory_size: usize,
userspace_addr: *mut u8,
mergeable: bool,
readonly: bool,
log_dirty: bool,
@@ -1731,10 +1760,11 @@ impl MemoryManager {
let slot = self.allocate_memory_slot();
info!(
"Creating userspace mapping: {guest_phys_addr:x} -> {userspace_addr:x} {memory_size:x}, slot {slot}"
"Creating userspace mapping: {guest_phys_addr:x} -> {userspace_addr_:x} {memory_size:x}, slot {slot}",
userspace_addr_ = userspace_addr as u64
);
// SAFETY: promised by caller
// SAFETY: caller promises parameters are correct.
unsafe {
self.vm
.create_user_memory_region(
@@ -1788,7 +1818,8 @@ impl MemoryManager {
}
info!(
"Created userspace mapping: {guest_phys_addr:x} -> {userspace_addr:x} {memory_size:x}"
"Created userspace mapping: {guest_phys_addr:x} -> {userspace_addr_:x} {memory_size:x}",
userspace_addr_ = userspace_addr as u64
);
Ok(slot)
@@ -1806,12 +1837,12 @@ impl MemoryManager {
pub unsafe fn remove_userspace_mapping(
&mut self,
guest_phys_addr: u64,
memory_size: u64,
userspace_addr: u64,
memory_size: usize,
userspace_addr: *mut u8,
mergeable: bool,
slot: u32,
) -> Result<(), Error> {
// SAFETY: The caller promises that the parameters are correct.
// SAFETY: Caller promises parameters are correct.
unsafe {
self.vm
.remove_user_memory_region(
@@ -1852,7 +1883,8 @@ impl MemoryManager {
}
info!(
"Removed userspace mapping: {guest_phys_addr:x} -> {userspace_addr:x} {memory_size:x}"
"Removed userspace mapping: {guest_phys_addr:x} -> {userspace_addr_:x} {memory_size:x}",
userspace_addr_ = userspace_addr as u64
);
Ok(())