FKIE_CVE-2026-68093

Vulnerability from fkie_nvd - Published: 2026-08-10 13:19 - Updated: 2026-08-19 17:20
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
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/0f33b1c457c2199ed130b92cc2ff363a3f7b9415
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/2028b81321dc757b6875b99c10d908e349c141e2
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/25f744ffa0c8e799e06250ce2e618367b166b0d4
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/60283726f2845bd78b95efbd0e50b93944780477
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/6b542d116acecb83a1ca34e8eace304cff6a4ec9
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/7508916b4b55d6f5ecc68cd09774dabd3a6b4440
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "arch/x86/kvm/svm/svm.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "2028b81321dc757b6875b99c10d908e349c141e2",
              "status": "affected",
              "version": "774c47f1d78e373a6bd2964f4e278d1ce26c21cb",
              "versionType": "git"
            },
            {
              "lessThan": "60283726f2845bd78b95efbd0e50b93944780477",
              "status": "affected",
              "version": "774c47f1d78e373a6bd2964f4e278d1ce26c21cb",
              "versionType": "git"
            },
            {
              "lessThan": "7508916b4b55d6f5ecc68cd09774dabd3a6b4440",
              "status": "affected",
              "version": "774c47f1d78e373a6bd2964f4e278d1ce26c21cb",
              "versionType": "git"
            },
            {
              "lessThan": "0f33b1c457c2199ed130b92cc2ff363a3f7b9415",
              "status": "affected",
              "version": "774c47f1d78e373a6bd2964f4e278d1ce26c21cb",
              "versionType": "git"
            },
            {
              "lessThan": "6b542d116acecb83a1ca34e8eace304cff6a4ec9",
              "status": "affected",
              "version": "774c47f1d78e373a6bd2964f4e278d1ce26c21cb",
              "versionType": "git"
            },
            {
              "lessThan": "25f744ffa0c8e799e06250ce2e618367b166b0d4",
              "status": "affected",
              "version": "774c47f1d78e373a6bd2964f4e278d1ce26c21cb",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "arch/x86/kvm/svm/svm.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.21"
            },
            {
              "lessThan": "2.6.21",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.183",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.148",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.101",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.42",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.6",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "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."
    }
  ],
  "id": "CVE-2026-68093",
  "lastModified": "2026-08-19T17:20:28.353",
  "metrics": {},
  "published": "2026-08-10T13:19:53.303",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "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"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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