KVM: SVM: Bump asid_generation on CPU online to avoid ASID collision after hotplug

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Summary

CVECVE-2026-68093
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-10 13:19:53 UTC
Updated2026-08-10 13:19:53 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: KVM: SVM: Bump asid_generation on CPU online to avoid ASID collision after hotplug If a vCPU stays scheduled out (or blocked) while the last pCPU it ran on goes through a hotplug cycle (online->offline->online), and the vCPU then resumes execution on the same pCPU, then it is possible for it to run with an ASID that has now been assigned to a different vCPU, resulting in stale TLB translations being used. svm_enable_virtualization_cpu() resets asid_generation to 1 and sets next_asid to max_asid + 1 on every CPU online event, including hotplug cycles. Because next_asid starts beyond the pool boundary, the first call to new_asid() after an online event always wraps the pool, incrementing asid_generation to 2 and assigning ASIDs starting from min_asid. Consider two vCPUs from different VMs, vCPU-A pinned to CPU-X holding asid_generation=2 and ASID=N from before the hotplug event: 1. CPU-X goes offline and back online: asid_generation resets to 1, next_asid = max_asid + 1. 2. One or more vCPUs migrate to CPU-X and call new_asid(), wrapping the pool and consuming ASIDs starting from min_asid. Eventually vCPU-B from a different VM is assigned asid_generation=2, ASID=N — the same ASID that vCPU-A held before the hotplug. 3. vCPU-A enters pre_svm_run() on CPU-X: current_vmcb->cpu is unchanged so the migration branch is skipped. Its saved asid_generation=2 matches sd->asid_generation=2, so the generation check silently passes and vCPU-A continues running with ASID=N — the same ASID just freshly assigned to vCPU-B. Both vCPUs from different VMs now run on CPU-X with the same ASID, causing them to share NPT TLB entries and producing stale translations. The collision manifests as a KVM internal error (Suberror: 1, emulation failure). The NPT page fault reports a faulting GPA far outside the VM's physical memory range — a sign of stale TLB translations being used. KVM falls back to instruction emulation, which fails on FPU/XSave instructions (XRSTOR, STMXCSR) that the emulator does not implement. Fix this by incrementing asid_generation instead of resetting it to 1 in svm_enable_virtualization_cpu(). On module load, asid_generation starts at 0 (memset) and the increment produces 1, identical to the old behaviour. On subsequent hotplug cycles the generation advances beyond any value a vCPU previously observed on this CPU, so the generation check in pre_svm_run() reliably forces new_asid() on every vCPU after every hotplug cycle.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 774c47f1d78e373a6bd2964f4e278d1ce26c21cb 60283726f2845bd78b95efbd0e50b93944780477 git Not specified
CNA Linux Linux affected 774c47f1d78e373a6bd2964f4e278d1ce26c21cb 7508916b4b55d6f5ecc68cd09774dabd3a6b4440 git Not specified
CNA Linux Linux affected 774c47f1d78e373a6bd2964f4e278d1ce26c21cb 0f33b1c457c2199ed130b92cc2ff363a3f7b9415 git Not specified
CNA Linux Linux affected 774c47f1d78e373a6bd2964f4e278d1ce26c21cb 6b542d116acecb83a1ca34e8eace304cff6a4ec9 git Not specified
CNA Linux Linux affected 774c47f1d78e373a6bd2964f4e278d1ce26c21cb 25f744ffa0c8e799e06250ce2e618367b166b0d4 git Not specified
CNA Linux Linux affected 2.6.21 Not specified
CNA Linux Linux unaffected 2.6.21 semver Not specified
CNA Linux Linux unaffected 6.6.148 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.101 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.42 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.6 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2-rc4 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/0f33b1c457c2199ed130b92cc2ff363a3f7b9415 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/7508916b4b55d6f5ecc68cd09774dabd3a6b4440 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/25f744ffa0c8e799e06250ce2e618367b166b0d4 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/60283726f2845bd78b95efbd0e50b93944780477 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/6b542d116acecb83a1ca34e8eace304cff6a4ec9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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