CVE-2026-68093
Full vulnerability record from the local CVENow database.
Description
In 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.
View original CVE JSON
{
"id": "CVE-2026-68093",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"published": "2026-08-10T13:19:53.303",
"lastModified": "2026-11-06T17:19:17.397",
"vulnStatus": "Received",
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: SVM: Bump asid_generation on CPU online to avoid ASID collision after hotplug\n\nIf a vCPU stays scheduled out (or blocked) while the last pCPU it ran\non goes through a hotplug cycle (online->offline->online), and the vCPU\nthen resumes execution on the same pCPU, then it is possible for it to\nrun with an ASID that has now been assigned to a different vCPU,\nresulting in stale TLB translations being used.\n\nsvm_enable_virtualization_cpu() resets asid_generation to 1 and sets\nnext_asid to max_asid + 1 on every CPU online event, including hotplug\ncycles. Because next_asid starts beyond the pool boundary, the first\ncall to new_asid() after an online event always wraps the pool,\nincrementing asid_generation to 2 and assigning ASIDs starting from\nmin_asid.\n\nConsider two vCPUs from different VMs, vCPU-A pinned to CPU-X holding\nasid_generation=2 and ASID=N from before the hotplug event:\n\n 1. CPU-X goes offline and back online: asid_generation resets to 1,\n next_asid = max_asid + 1.\n\n 2. One or more vCPUs migrate to CPU-X and call new_asid(), wrapping\n the pool and consuming ASIDs starting from min_asid. Eventually\n vCPU-B from a different VM is assigned asid_generation=2, ASID=N\n — the same ASID that vCPU-A held before the hotplug.\n\n 3. vCPU-A enters pre_svm_run() on CPU-X: current_vmcb->cpu is\n unchanged so the migration branch is skipped. Its saved\n asid_generation=2 matches sd->asid_generation=2, so the generation\n check silently passes and vCPU-A continues running with ASID=N —\n the same ASID just freshly assigned to vCPU-B.\n\nBoth vCPUs from different VMs now run on CPU-X with the same ASID,\ncausing them to share NPT TLB entries and producing stale translations.\n\nThe collision manifests as a KVM internal error (Suberror: 1, emulation\nfailure). The NPT page fault reports a faulting GPA far outside the\nVM's physical memory range — a sign of stale TLB translations being\nused. KVM falls back to instruction emulation, which fails on\nFPU/XSave instructions (XRSTOR, STMXCSR) that the emulator does not\nimplement.\n\nFix this by incrementing asid_generation instead of resetting it to 1\nin svm_enable_virtualization_cpu(). On module load, asid_generation\nstarts at 0 (memset) and the increment produces 1, identical to the\nold behaviour. On subsequent hotplug cycles the generation advances\nbeyond any value a vCPU previously observed on this CPU, so the\ngeneration check in pre_svm_run() reliably forces new_asid() on every\nvCPU after every hotplug cycle."
}
],
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
"vendor": "Linux",
"product": "Linux",
"defaultStatus": "unaffected",
"programFiles": [
"arch/x86/kvm/svm/svm.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"versions": [
{
"version": "774c47f1d78e373a6bd2964f4e278d1ce26c21cb",
"lessThan": "2028b81321dc757b6875b99c10d908e349c141e2",
"versionType": "git",
"status": "affected"
},
{
"version": "774c47f1d78e373a6bd2964f4e278d1ce26c21cb",
"lessThan": "60283726f2845bd78b95efbd0e50b93944780477",
"versionType": "git",
"status": "affected"
},
{
"version": "774c47f1d78e373a6bd2964f4e278d1ce26c21cb",
"lessThan": "7508916b4b55d6f5ecc68cd09774dabd3a6b4440",
"versionType": "git",
"status": "affected"
},
{
"version": "774c47f1d78e373a6bd2964f4e278d1ce26c21cb",
"lessThan": "0f33b1c457c2199ed130b92cc2ff363a3f7b9415",
"versionType": "git",
"status": "affected"
},
{
"version": "774c47f1d78e373a6bd2964f4e278d1ce26c21cb",
"lessThan": "6b542d116acecb83a1ca34e8eace304cff6a4ec9",
"versionType": "git",
"status": "affected"
},
{
"version": "774c47f1d78e373a6bd2964f4e278d1ce26c21cb",
"lessThan": "25f744ffa0c8e799e06250ce2e618367b166b0d4",
"versionType": "git",
"status": "affected"
}
]
},
{
"vendor": "Linux",
"product": "Linux",
"defaultStatus": "affected",
"programFiles": [
"arch/x86/kvm/svm/svm.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"versions": [
{
"version": "2.6.21",
"status": "affected"
},
{
"version": "0",
"lessThan": "2.6.21",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.1.183",
"lessThanOrEqual": "6.1.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.6.148",
"lessThanOrEqual": "6.6.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.12.101",
"lessThanOrEqual": "6.12.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.18.42",
"lessThanOrEqual": "6.18.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "7.1.6",
"lessThanOrEqual": "7.1.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "7.2",
"lessThanOrEqual": "*",
"versionType": "original_commit_for_fix",
"status": "unaffected"
}
]
}
]
}
],
"metrics": {
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"timestamp": "2026-11-06T16:42:24.942470Z",
"id": "CVE-2026-68093",
"options": [
{
"exploitation": "none"
},
{
"automatable": "no"
},
{
"technicalImpact": "partial"
}
],
"role": "CISA Coordinator",
"version": "2.0.3"
}
}
]
},
"references": [
{
"url": "https://git.kernel.org/stable/c/0f33b1c457c2199ed130b92cc2ff363a3f7b9415",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/2028b81321dc757b6875b99c10d908e349c141e2",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/25f744ffa0c8e799e06250ce2e618367b166b0d4",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/60283726f2845bd78b95efbd0e50b93944780477",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/6b542d116acecb83a1ca34e8eace304cff6a4ec9",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/7508916b4b55d6f5ecc68cd09774dabd3a6b4440",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
]
}