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virtio-devices: iommu: Reject UNMAP that partially overlaps a mapping

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An UNMAP that would split an existing mapping must be rejected with
VIRTIO_IOMMU_S_RANGE without removing anything. The previous start-only
retain silently left mappings that started outside the unmap range but
overlapped it.

Walk bookkeeping under a read lock and reject before touching VFIO so a
rejection cannot leave VFIO and bookkeeping out of sync.

Signed-off-by: Rob Bradford <rbradford@meta.com>
Assisted-by: Claude:claude-opus-4-7
This commit is contained in:
Rob Bradford
2026-04-26 16:36:12 +01:00
parent 7989e46f8b
commit 4d6c7c95c0
1 changed files with 34 additions and 9 deletions
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43
virtio-devices/src/iommu.rs
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@@ -322,6 +322,8 @@ enum Error {
InvalidUnmapRequestBypassDomain,
#[error("Invalid to unmap because the domain is missing")]
InvalidUnmapRequestMissingDomain,
#[error("UNMAP range partially overlaps an existing mapping")]
InvalidUnmapRequestPartialOverlap,
#[error("Guest sent us invalid PROBE request")]
InvalidProbeRequest,
#[error("Failed to performing external mapping")]
@@ -561,6 +563,38 @@ impl Request {
return Err(Error::InvalidUnmapRequestMissingDomain);
}
let Some(size) = req
.virt_end
.checked_sub(virt_start)
.and_then(|d| d.checked_add(1))
else {
status = VIRTIO_IOMMU_S_RANGE;
return Err(Error::InvalidUnmapRequest);
};
// An UNMAP that would split an existing mapping must be
// rejected with VIRTIO_IOMMU_S_RANGE without removing
// anything. Inspect bookkeeping before touching VFIO so
// a rejection cannot leave VFIO out of sync.
{
let domains = mapping.domains.read().unwrap();
let Some(domain) = domains.get(&domain_id) else {
status = VIRTIO_IOMMU_S_INVAL;
return Err(Error::InvalidUnmapRequestMissingDomain);
};
for (&start, m) in domain.mappings.iter() {
let Some(end) = inclusive_end(start, m.size) else {
continue;
};
let overlaps = start <= req.virt_end && end >= req.virt_start;
let split = start < req.virt_start || end > req.virt_end;
if overlaps && split {
status = VIRTIO_IOMMU_S_RANGE;
return Err(Error::InvalidUnmapRequestPartialOverlap);
}
}
}
// Find the list of endpoints attached to the given domain.
let endpoints: Vec<u32> = mapping
.endpoints
@@ -571,15 +605,6 @@ impl Request {
.map(|(&e, _)| e)
.collect();
let Some(size) = req
.virt_end
.checked_sub(virt_start)
.and_then(|d| d.checked_add(1))
else {
status = VIRTIO_IOMMU_S_RANGE;
return Err(Error::InvalidUnmapRequest);
};
// Trigger external unmapping if necessary.
for endpoint in endpoints {
if let Some(ext_map) = ext_mapping.get(&endpoint) {