CVE-2025-40300 (GCVE-0-2025-40300)

Vulnerability from cvelistv5 – Published: 2025-09-11 16:49 – Updated: 2026-01-02 15:33
VLAI?
Title
x86/vmscape: Add conditional IBPB mitigation
Summary
In the Linux kernel, the following vulnerability has been resolved: x86/vmscape: Add conditional IBPB mitigation VMSCAPE is a vulnerability that exploits insufficient branch predictor isolation between a guest and a userspace hypervisor (like QEMU). Existing mitigations already protect kernel/KVM from a malicious guest. Userspace can additionally be protected by flushing the branch predictors after a VMexit. Since it is the userspace that consumes the poisoned branch predictors, conditionally issue an IBPB after a VMexit and before returning to userspace. Workloads that frequently switch between hypervisor and userspace will incur the most overhead from the new IBPB. This new IBPB is not integrated with the existing IBPB sites. For instance, a task can use the existing speculation control prctl() to get an IBPB at context switch time. With this implementation, the IBPB is doubled up: one at context switch and another before running userspace. The intent is to integrate and optimize these cases post-embargo. [ dhansen: elaborate on suboptimal IBPB solution ]
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 15d45071523d89b3fb7372e2135fbd72f6af9506 , < ac60717f9a8d21c58617d0b34274babf24135835 (git)
Affected: 15d45071523d89b3fb7372e2135fbd72f6af9506 , < c08192b5d6730a914dee6175bc71092ee6a65f14 (git)
Affected: 15d45071523d89b3fb7372e2135fbd72f6af9506 , < d5490dfa35427a2967e00a4c7a1b95fdbc8ede34 (git)
Affected: 15d45071523d89b3fb7372e2135fbd72f6af9506 , < 2f4f2f8f860cb4c3336a7435ebe8dcfded0c9c6e (git)
Affected: 15d45071523d89b3fb7372e2135fbd72f6af9506 , < 15006289e5c38b2a830e1fba221977a27598176c (git)
Affected: 15d45071523d89b3fb7372e2135fbd72f6af9506 , < 893387c18612bb452336a5881da0d015a7e8f4a2 (git)
Affected: 15d45071523d89b3fb7372e2135fbd72f6af9506 , < f866eef8d1c65504d30923c3f14082ad294d0e6d (git)
Affected: 15d45071523d89b3fb7372e2135fbd72f6af9506 , < 34e5667041050711a947e260fc9ebebe08bddee5 (git)
Affected: 15d45071523d89b3fb7372e2135fbd72f6af9506 , < d7ddc93392e4a7ffcccc86edf6ef3e64c778db52 (git)
Affected: 15d45071523d89b3fb7372e2135fbd72f6af9506 , < 459274c77b37ac63b78c928b4b4e748d1f9d05c8 (git)
Affected: 15d45071523d89b3fb7372e2135fbd72f6af9506 , < 510603f504796c3535f67f55fb0b124a303b44c8 (git)
Affected: 15d45071523d89b3fb7372e2135fbd72f6af9506 , < 9c23a90648e831d611152ac08dbcd1283d405e7f (git)
Affected: 15d45071523d89b3fb7372e2135fbd72f6af9506 , < 2f8f173413f1cbf52660d04df92d0069c4306d25 (git)
Affected: c51f1e5f57cca88d8d5894b6fad1638f643a99d0 (git)
Affected: 4b3870c343a82cd2df7192cc5149c87205dcc611 (git)
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    Linux Linux Affected: 4.16
Unaffected: 0 , < 4.16 (semver)
Unaffected: 5.10.244 , ≤ 5.10.* (semver)
Unaffected: 5.15.193 , ≤ 5.15.* (semver)
Unaffected: 6.1.152 , ≤ 6.1.* (semver)
Unaffected: 6.6.106 , ≤ 6.6.* (semver)
Unaffected: 6.12.47 , ≤ 6.12.* (semver)
Unaffected: 6.16.7 , ≤ 6.16.* (semver)
Unaffected: 6.17 , ≤ * (original_commit_for_fix)
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        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/vmscape: Add conditional IBPB mitigation\n\nVMSCAPE is a vulnerability that exploits insufficient branch predictor\nisolation between a guest and a userspace hypervisor (like QEMU). Existing\nmitigations already protect kernel/KVM from a malicious guest. Userspace\ncan additionally be protected by flushing the branch predictors after a\nVMexit.\n\nSince it is the userspace that consumes the poisoned branch predictors,\nconditionally issue an IBPB after a VMexit and before returning to\nuserspace. Workloads that frequently switch between hypervisor and\nuserspace will incur the most overhead from the new IBPB.\n\nThis new IBPB is not integrated with the existing IBPB sites. For\ninstance, a task can use the existing speculation control prctl() to\nget an IBPB at context switch time. With this implementation, the\nIBPB is doubled up: one at context switch and another before running\nuserspace.\n\nThe intent is to integrate and optimize these cases post-embargo.\n\n[ dhansen: elaborate on suboptimal IBPB solution ]"
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        },
        {
          "url": "https://git.kernel.org/stable/c/2f8f173413f1cbf52660d04df92d0069c4306d25"
        }
      ],
      "title": "x86/vmscape: Add conditional IBPB mitigation",
      "x_generator": {
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-40300",
    "datePublished": "2025-09-11T16:49:24.809Z",
    "dateReserved": "2025-04-16T07:20:57.185Z",
    "dateUpdated": "2026-01-02T15:33:23.260Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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  • 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.
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  • 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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