CVE-2026-68093 (GCVE-0-2026-68093)

Vulnerability from cvelistv5 – Published: 2026-08-10 11:58 – Updated: 2026-08-19 16:29
VLAI
Title
KVM: SVM: Bump asid_generation on CPU online to avoid ASID collision after hotplug
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.
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 774c47f1d78e373a6bd2964f4e278d1ce26c21cb , < 2028b81321dc757b6875b99c10d908e349c141e2 (git)
Affected: 774c47f1d78e373a6bd2964f4e278d1ce26c21cb , < 60283726f2845bd78b95efbd0e50b93944780477 (git)
Affected: 774c47f1d78e373a6bd2964f4e278d1ce26c21cb , < 7508916b4b55d6f5ecc68cd09774dabd3a6b4440 (git)
Affected: 774c47f1d78e373a6bd2964f4e278d1ce26c21cb , < 0f33b1c457c2199ed130b92cc2ff363a3f7b9415 (git)
Affected: 774c47f1d78e373a6bd2964f4e278d1ce26c21cb , < 6b542d116acecb83a1ca34e8eace304cff6a4ec9 (git)
Affected: 774c47f1d78e373a6bd2964f4e278d1ce26c21cb , < 25f744ffa0c8e799e06250ce2e618367b166b0d4 (git)
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Linux Linux Affected: 2.6.21
Unaffected: 0 , < 2.6.21 (semver)
Unaffected: 6.1.183 , ≤ 6.1.* (semver)
Unaffected: 6.6.148 , ≤ 6.6.* (semver)
Unaffected: 6.12.101 , ≤ 6.12.* (semver)
Unaffected: 6.18.42 , ≤ 6.18.* (semver)
Unaffected: 7.1.6 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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{
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          "product": "Linux",
          "programFiles": [
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      "cpeApplicability": [
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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"
        },
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        },
        {
          "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",
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      }
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    "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"
  },
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  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-68093",
      "date": "2026-08-20",
      "epss": "0.00186",
      "percentile": "0.08475"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-68093\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-08-10T13:19:53.303\",\"lastModified\":\"2026-08-19T17:20:28.353\",\"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-\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.\"}],\"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\":{},\"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\"}]}}",
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-13T13:30:51+00:00",
      "cve": "CVE-2026-68093",
      "id": "CVE-2026-68093",
      "initial_release_date": "2026-08-10T00:00:00+00:00",
      "product_status:known_affected": "233",
      "product_status:known_not_affected": "43",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: KVM: SVM: Bump asid_generation on CPU online to avoid ASID collision after hotplug",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-68093.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-08-11T23:48:38Z",
      "cve": "CVE-2026-68093",
      "id": "CVE-2026-68093",
      "initial_release_date": "2026-08-11T23:48:38Z",
      "product_status:known_affected": "12",
      "product_status:known_not_affected": "284",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-68093",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-68093.json",
      "version": "2"
    }
  }
}



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