Vulnerability-Lookup

GHSA-J396-GV6V-75WX

Vulnerability from github – Published: 2026-10-18 18:32 – Updated: 2026-10-18 18:32

Details

In the Linux kernel, the following vulnerability has been resolved:

KVM: SVM: Preserve TLB control (i.e. pending TLB flush) on failed VMRUN

Don't reset the VMCB's TLB control back to "do nothing" on a failed VMRUN, as empirical testing shows that the CPU performs the requested TLB flush if and only if VMRUN is successful, i.e. clearing TLB control on a failed VMRUN effectively drops a TLB flush.

Explicitly track the need to flush all ASIDs on a per-CPU basis, as the ASID reuse condition is tied to the pCPU, not to the vCPU. As a bonus, this also obviates the need to avoid clobbering FLUSH_ALL_ASID with TLB_CONTROL_FLUSH_ASID, e.g. in svm_flush_tlb_asid().

Deliberately don't bother saving/restoring the "old" tlb_ctl on failure, in quotes because it's not exactly the old tlb_ctl, it's the tlb_ctl from after pre_svm_run(), but before updating tlb_ctl for flush_all_asids. If VMRUN fails and TLB_CONTROL_FLUSH_ALL_ASID is forced, then the next successful run of the VMCB may unnecessarily flush all ASIDs, which strictly speaking could result in noisy neighbor issues. However, the fact that new_asid() is already guest-triggerable, because of KVM's flawed behavior of clearing the ASID on emulated INIT, means that a guest can already trigger a flush of all ASIDs at roughly the same rate. And once KVM stops clobbering the ASID on emulated INIT, or assigns a static ASID to each vCPU, this flaw goes away.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-98715"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-18T16:17:25Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: SVM: Preserve TLB control (i.e. pending TLB flush) on failed VMRUN\n\nDon\u0027t reset the VMCB\u0027s TLB control back to \"do nothing\" on a failed VMRUN,\nas empirical testing shows that the CPU performs the requested TLB flush if\nand only if VMRUN is successful, i.e. clearing TLB control on a failed\nVMRUN effectively drops a TLB flush.\n\nExplicitly track the need to flush all ASIDs on a per-CPU basis, as the\nASID reuse condition is tied to the pCPU, not to the vCPU.  As a bonus,\nthis also obviates the need to avoid clobbering FLUSH_ALL_ASID with\nTLB_CONTROL_FLUSH_ASID, e.g. in svm_flush_tlb_asid().\n\nDeliberately don\u0027t bother saving/restoring the \"old\" tlb_ctl on failure,\nin quotes because it\u0027s not exactly the old tlb_ctl, it\u0027s the tlb_ctl from\nafter pre_svm_run(), but before updating tlb_ctl for flush_all_asids.  If\nVMRUN fails and TLB_CONTROL_FLUSH_ALL_ASID is forced, then the next\nsuccessful run of the VMCB *may* unnecessarily flush all ASIDs, which\nstrictly speaking could result in noisy neighbor issues.  However, the\nfact that new_asid() is already guest-triggerable, because of KVM\u0027s flawed\nbehavior of clearing the ASID on emulated INIT, means that a guest can\nalready trigger a flush of all ASIDs at roughly the same rate.  And once\nKVM stops clobbering the ASID on emulated INIT, *or* assigns a static ASID\nto each vCPU, this flaw goes away.",
  "id": "GHSA-j396-gv6v-75wx",
  "modified": "2026-10-18T18:32:00Z",
  "published": "2026-10-18T18:32:00Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98715"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/60d93c27859fb3ec5b5a689e24de303f166477d0"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/fd873c3d1b5240e80365f09e758e8c96b88a7cdb"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

CVE-2026-98715 (GCVE-0-2026-98715)

Vulnerability from cvelistv5 – Published: 2026-10-18 15:46 – Updated: 2026-10-19 09:24

Title

KVM: SVM: Preserve TLB control (i.e. pending TLB flush) on failed VMRUN

Summary

In the Linux kernel, the following vulnerability has been resolved: KVM: SVM: Preserve TLB control (i.e. pending TLB flush) on failed VMRUN Don't reset the VMCB's TLB control back to "do nothing" on a failed VMRUN, as empirical testing shows that the CPU performs the requested TLB flush if and only if VMRUN is successful, i.e. clearing TLB control on a failed VMRUN effectively drops a TLB flush. Explicitly track the need to flush all ASIDs on a per-CPU basis, as the ASID reuse condition is tied to the pCPU, not to the vCPU. As a bonus, this also obviates the need to avoid clobbering FLUSH_ALL_ASID with TLB_CONTROL_FLUSH_ASID, e.g. in svm_flush_tlb_asid(). Deliberately don't bother saving/restoring the "old" tlb_ctl on failure, in quotes because it's not exactly the old tlb_ctl, it's the tlb_ctl from after pre_svm_run(), but before updating tlb_ctl for flush_all_asids. If VMRUN fails and TLB_CONTROL_FLUSH_ALL_ASID is forced, then the next successful run of the VMCB *may* unnecessarily flush all ASIDs, which strictly speaking could result in noisy neighbor issues. However, the fact that new_asid() is already guest-triggerable, because of KVM's flawed behavior of clearing the ASID on emulated INIT, means that a guest can already trigger a flush of all ASIDs at roughly the same rate. And once KVM stops clobbering the ASID on emulated INIT, *or* assigns a static ASID to each vCPU, this flaw goes away.

Severity

No CVSS data available.

Assigner

Linux CNA under the mitre root

CNA scorecard D 53/100 over 6820 records in the last 180 days details

References

2 references

URL	Tags
https://git.kernel.org/stable/c/fd873c3d1b5240e80…
https://git.kernel.org/stable/c/60d93c27859fb3ec5…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 38e5e92fe8c02a8766459d505423b855caf9af1f , < fd873c3d1b5240e80365f09e758e8c96b88a7cdb (git) Affected: 38e5e92fe8c02a8766459d505423b855caf9af1f , < 60d93c27859fb3ec5b5a689e24de303f166477d0 (git)
Linux	Linux	Affected: 2.6.38 Unaffected: 0 , < 2.6.38 (semver) Unaffected: 7.2.10 , ≤ 7.2.* (semver) Unaffected: 7.3 , ≤ * (original_commit_for_fix)

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "arch/x86/kvm/svm/svm.c",
            "arch/x86/kvm/svm/svm.h"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "fd873c3d1b5240e80365f09e758e8c96b88a7cdb",
              "status": "affected",
              "version": "38e5e92fe8c02a8766459d505423b855caf9af1f",
              "versionType": "git"
            },
            {
              "lessThan": "60d93c27859fb3ec5b5a689e24de303f166477d0",
              "status": "affected",
              "version": "38e5e92fe8c02a8766459d505423b855caf9af1f",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "arch/x86/kvm/svm/svm.c",
            "arch/x86/kvm/svm/svm.h"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.38"
            },
            {
              "lessThan": "2.6.38",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.10",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.10",
                  "versionStartIncluding": "2.6.38",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "2.6.38",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: SVM: Preserve TLB control (i.e. pending TLB flush) on failed VMRUN\n\nDon\u0027t reset the VMCB\u0027s TLB control back to \"do nothing\" on a failed VMRUN,\nas empirical testing shows that the CPU performs the requested TLB flush if\nand only if VMRUN is successful, i.e. clearing TLB control on a failed\nVMRUN effectively drops a TLB flush.\n\nExplicitly track the need to flush all ASIDs on a per-CPU basis, as the\nASID reuse condition is tied to the pCPU, not to the vCPU.  As a bonus,\nthis also obviates the need to avoid clobbering FLUSH_ALL_ASID with\nTLB_CONTROL_FLUSH_ASID, e.g. in svm_flush_tlb_asid().\n\nDeliberately don\u0027t bother saving/restoring the \"old\" tlb_ctl on failure,\nin quotes because it\u0027s not exactly the old tlb_ctl, it\u0027s the tlb_ctl from\nafter pre_svm_run(), but before updating tlb_ctl for flush_all_asids.  If\nVMRUN fails and TLB_CONTROL_FLUSH_ALL_ASID is forced, then the next\nsuccessful run of the VMCB *may* unnecessarily flush all ASIDs, which\nstrictly speaking could result in noisy neighbor issues.  However, the\nfact that new_asid() is already guest-triggerable, because of KVM\u0027s flawed\nbehavior of clearing the ASID on emulated INIT, means that a guest can\nalready trigger a flush of all ASIDs at roughly the same rate.  And once\nKVM stops clobbering the ASID on emulated INIT, *or* assigns a static ASID\nto each vCPU, this flaw goes away."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:24:26.247Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/fd873c3d1b5240e80365f09e758e8c96b88a7cdb"
        },
        {
          "url": "https://git.kernel.org/stable/c/60d93c27859fb3ec5b5a689e24de303f166477d0"
        }
      ],
      "title": "KVM: SVM: Preserve TLB control (i.e. pending TLB flush) on failed VMRUN",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98715",
    "datePublished": "2026-10-18T15:46:47.988Z",
    "dateReserved": "2026-09-25T10:25:14.366Z",
    "dateUpdated": "2026-10-19T09:24:26.247Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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