FKIE_CVE-2026-98715

Vulnerability from fkie_nvd - Published: 2026-10-18 16:17 - Updated: 2026-10-19 10:19
Severity
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.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/60d93c27859fb3ec5b5a689e24de303f166477d0
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/fd873c3d1b5240e80365f09e758e8c96b88a7cdb
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "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"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "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."
    }
  ],
  "id": "CVE-2026-98715",
  "lastModified": "2026-10-19T10:19:35.747",
  "metrics": {},
  "published": "2026-10-18T16:17:25.050",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/60d93c27859fb3ec5b5a689e24de303f166477d0"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/fd873c3d1b5240e80365f09e758e8c96b88a7cdb"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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