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misc: Work around vfio_dma_map being unsound

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This API passes a u64 to a kernel API that treats the u64 as a userspace
address.  Therefore, it should be marked unsafe, but it currently is not
[1].  Wrap the call in an unsafe block to document that invariants must
be upheld to avoid undefined behavior.  This causes a compiler warning,
so suppress the warning with #[allow(unused_unsafe)].

[1]: https://github.com/rust-vmm/vfio/issues/100

Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
This commit is contained in:
Demi Marie Obenour
2025-06-27 19:17:00 -04:00
committed by Rob Bradford
parent 12c7cc5e4f
commit 8be28f8438
3 changed files with 107 additions and 37 deletions
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24
vmm/src/device_manager.rs
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@@ -3754,13 +3754,19 @@ impl DeviceManager {
// virtio-mem device itself.
for (_, zone) in self.memory_manager.lock().unwrap().memory_zones().iter() {
for region in zone.regions() {
vfio_container
.vfio_dma_map(
// vfio_dma_map is unsound and ought to be marked as unsafe
#[allow(unused_unsafe)]
// SAFETY: GuestMemoryMmap guarantees that region points
// to len bytes of valid memory starting at as_ptr()
// that will only be freed with munmap().
unsafe {
vfio_container.vfio_dma_map(
region.start_addr().raw_value(),
region.len(),
region.as_ptr() as u64,
)
.map_err(DeviceManagerError::VfioDmaMap)?;
}
.map_err(DeviceManagerError::VfioDmaMap)?;
}
}
@@ -4368,13 +4374,19 @@ impl DeviceManager {
// Take care of updating the memory for VFIO PCI devices.
if let Some(vfio_container) = &self.vfio_container {
vfio_container
.vfio_dma_map(
// vfio_dma_map is unsound and ought to be marked as unsafe
#[allow(unused_unsafe)]
// SAFETY: GuestMemoryMmap guarantees that region points
// to len bytes of valid memory starting at as_ptr()
// that will only be freed with munmap().
unsafe {
vfio_container.vfio_dma_map(
new_region.start_addr().raw_value(),
new_region.len(),
new_region.as_ptr() as u64,
)
.map_err(DeviceManagerError::UpdateMemoryForVfioPciDevice)?;
}
.map_err(DeviceManagerError::UpdateMemoryForVfioPciDevice)?;
}
// Take care of updating the memory for vfio-user devices.