CVE-2026-68093 (GCVE-0-2026-68093)
Vulnerability from cvelistv5
Published
2026-08-10 11:58
Modified
2026-08-19 16:29
Severity ?
Summary
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.
References
Impacted products
Vendor Product Version
Linux Linux Version: 774c47f1d78e373a6bd2964f4e278d1ce26c21cb
Version: 774c47f1d78e373a6bd2964f4e278d1ce26c21cb
Version: 774c47f1d78e373a6bd2964f4e278d1ce26c21cb
Version: 774c47f1d78e373a6bd2964f4e278d1ce26c21cb
Version: 774c47f1d78e373a6bd2964f4e278d1ce26c21cb
Version: 774c47f1d78e373a6bd2964f4e278d1ce26c21cb
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{
  "containers": {
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "arch/x86/kvm/svm/svm.c"
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          "programFiles": [
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          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "version": "0",
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              "version": "7.1.6",
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            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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              "negate": false,
              "operator": "OR"
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      "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-\u003eoffline-\u003eonline), 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     \u2014 the same ASID that vCPU-A held before the hotplug.\n\n  3. vCPU-A enters pre_svm_run() on CPU-X: current_vmcb-\u003ecpu is\n     unchanged so the migration branch is skipped.  Its saved\n     asid_generation=2 matches sd-\u003easid_generation=2, so the generation\n     check silently passes and vCPU-A continues running with ASID=N \u2014\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\u0027s physical memory range \u2014 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."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-19T16:29:15.060Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/2028b81321dc757b6875b99c10d908e349c141e2"
        },
        {
          "url": "https://git.kernel.org/stable/c/60283726f2845bd78b95efbd0e50b93944780477"
        },
        {
          "url": "https://git.kernel.org/stable/c/7508916b4b55d6f5ecc68cd09774dabd3a6b4440"
        },
        {
          "url": "https://git.kernel.org/stable/c/0f33b1c457c2199ed130b92cc2ff363a3f7b9415"
        },
        {
          "url": "https://git.kernel.org/stable/c/6b542d116acecb83a1ca34e8eace304cff6a4ec9"
        },
        {
          "url": "https://git.kernel.org/stable/c/25f744ffa0c8e799e06250ce2e618367b166b0d4"
        }
      ],
      "title": "KVM: SVM: Bump asid_generation on CPU online to avoid ASID collision after hotplug",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-68093",
    "datePublished": "2026-08-10T11:58:05.933Z",
    "dateReserved": "2026-07-30T09:28:09.367Z",
    "dateUpdated": "2026-08-19T16:29:15.060Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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