CVE-2025-40026 (GCVE-0-2025-40026)
Vulnerability from cvelistv5
Published
2025-10-28 09:32
Modified
2025-10-29 13:19
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Don't (re)check L1 intercepts when completing userspace I/O When completing emulation of instruction that generated a userspace exit for I/O, don't recheck L1 intercepts as KVM has already finished that phase of instruction execution, i.e. has already committed to allowing L2 to perform I/O. If L1 (or host userspace) modifies the I/O permission bitmaps during the exit to userspace, KVM will treat the access as being intercepted despite already having emulated the I/O access. Pivot on EMULTYPE_NO_DECODE to detect that KVM is completing emulation. Of the three users of EMULTYPE_NO_DECODE, only complete_emulated_io() (the intended "recipient") can reach the code in question. gp_interception()'s use is mutually exclusive with is_guest_mode(), and complete_emulated_insn_gp() unconditionally pairs EMULTYPE_NO_DECODE with EMULTYPE_SKIP. The bad behavior was detected by a syzkaller program that toggles port I/O interception during the userspace I/O exit, ultimately resulting in a WARN on vcpu->arch.pio.count being non-zero due to KVM no completing emulation of the I/O instruction. WARNING: CPU: 23 PID: 1083 at arch/x86/kvm/x86.c:8039 emulator_pio_in_out+0x154/0x170 [kvm] Modules linked in: kvm_intel kvm irqbypass CPU: 23 UID: 1000 PID: 1083 Comm: repro Not tainted 6.16.0-rc5-c1610d2d66b1-next-vm #74 NONE Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:emulator_pio_in_out+0x154/0x170 [kvm] PKRU: 55555554 Call Trace: <TASK> kvm_fast_pio+0xd6/0x1d0 [kvm] vmx_handle_exit+0x149/0x610 [kvm_intel] kvm_arch_vcpu_ioctl_run+0xda8/0x1ac0 [kvm] kvm_vcpu_ioctl+0x244/0x8c0 [kvm] __x64_sys_ioctl+0x8a/0xd0 do_syscall_64+0x5d/0xc60 entry_SYSCALL_64_after_hwframe+0x4b/0x53 </TASK>
References
Impacted products
Vendor Product Version
Linux Linux Version: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9
Version: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9
Version: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9
Version: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9
Version: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9
Version: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9
Version: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9
Version: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9
Version: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "arch/x86/kvm/emulate.c",
            "arch/x86/kvm/kvm_emulate.h",
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        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "arch/x86/kvm/emulate.c",
            "arch/x86/kvm/kvm_emulate.h",
            "arch/x86/kvm/x86.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "status": "affected",
              "version": "3.0"
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              "status": "unaffected",
              "version": "0",
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              "status": "unaffected",
              "version": "5.4.301",
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              "status": "unaffected",
              "version": "5.10.246",
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              "status": "unaffected",
              "version": "5.15.195",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.157",
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            },
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              "status": "unaffected",
              "version": "6.6.111",
              "versionType": "semver"
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              "status": "unaffected",
              "version": "6.12.52",
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              "status": "unaffected",
              "version": "6.16.12",
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              "lessThanOrEqual": "6.17.*",
              "status": "unaffected",
              "version": "6.17.2",
              "versionType": "semver"
            },
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              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.18-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
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          "nodes": [
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                  "versionEndExcluding": "5.4.301",
                  "versionStartIncluding": "3.0",
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                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86: Don\u0027t (re)check L1 intercepts when completing userspace I/O\n\nWhen completing emulation of instruction that generated a userspace exit\nfor I/O, don\u0027t recheck L1 intercepts as KVM has already finished that\nphase of instruction execution, i.e. has already committed to allowing L2\nto perform I/O.  If L1 (or host userspace) modifies the I/O permission\nbitmaps during the exit to userspace,  KVM will treat the access as being\nintercepted despite already having emulated the I/O access.\n\nPivot on EMULTYPE_NO_DECODE to detect that KVM is completing emulation.\nOf the three users of EMULTYPE_NO_DECODE, only complete_emulated_io() (the\nintended \"recipient\") can reach the code in question.  gp_interception()\u0027s\nuse is mutually exclusive with is_guest_mode(), and\ncomplete_emulated_insn_gp() unconditionally pairs EMULTYPE_NO_DECODE with\nEMULTYPE_SKIP.\n\nThe bad behavior was detected by a syzkaller program that toggles port I/O\ninterception during the userspace I/O exit, ultimately resulting in a WARN\non vcpu-\u003earch.pio.count being non-zero due to KVM no completing emulation\nof the I/O instruction.\n\n  WARNING: CPU: 23 PID: 1083 at arch/x86/kvm/x86.c:8039 emulator_pio_in_out+0x154/0x170 [kvm]\n  Modules linked in: kvm_intel kvm irqbypass\n  CPU: 23 UID: 1000 PID: 1083 Comm: repro Not tainted 6.16.0-rc5-c1610d2d66b1-next-vm #74 NONE\n  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\n  RIP: 0010:emulator_pio_in_out+0x154/0x170 [kvm]\n  PKRU: 55555554\n  Call Trace:\n   \u003cTASK\u003e\n   kvm_fast_pio+0xd6/0x1d0 [kvm]\n   vmx_handle_exit+0x149/0x610 [kvm_intel]\n   kvm_arch_vcpu_ioctl_run+0xda8/0x1ac0 [kvm]\n   kvm_vcpu_ioctl+0x244/0x8c0 [kvm]\n   __x64_sys_ioctl+0x8a/0xd0\n   do_syscall_64+0x5d/0xc60\n   entry_SYSCALL_64_after_hwframe+0x4b/0x53\n   \u003c/TASK\u003e"
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-10-29T13:19:27.308Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/a908eca437789589dd4624da428614c1275064dc"
        },
        {
          "url": "https://git.kernel.org/stable/c/00338255bb1f422642fb2798ebe92e93b6e4209b"
        },
        {
          "url": "https://git.kernel.org/stable/c/e0ce3ed1048a47986d15aef1a98ebda25560d257"
        },
        {
          "url": "https://git.kernel.org/stable/c/ba35a5d775799ce5ad60230be97336f2fefd518e"
        },
        {
          "url": "https://git.kernel.org/stable/c/3d3abf3f7e8b1abb082070a343de82d7efc80523"
        },
        {
          "url": "https://git.kernel.org/stable/c/e7177c7e32cb806f348387b7f4faafd4a5b32054"
        },
        {
          "url": "https://git.kernel.org/stable/c/3a062a5c55adc5507600b9ae6d911e247e2f1d6e"
        },
        {
          "url": "https://git.kernel.org/stable/c/7366830642505683bbe905a2ba5d18d6e4b512b8"
        },
        {
          "url": "https://git.kernel.org/stable/c/e750f85391286a4c8100275516973324b621a269"
        }
      ],
      "title": "KVM: x86: Don\u0027t (re)check L1 intercepts when completing userspace I/O",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-40026",
    "datePublished": "2025-10-28T09:32:33.075Z",
    "dateReserved": "2025-04-16T07:20:57.152Z",
    "dateUpdated": "2025-10-29T13:19:27.308Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.1",
  "vulnerability-lookup:meta": {
    "nvd": "{\"cve\":{\"id\":\"CVE-2025-40026\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2025-10-28T10:15:42.167\",\"lastModified\":\"2025-10-30T15:05:32.197\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nKVM: x86: Don\u0027t (re)check L1 intercepts when completing userspace I/O\\n\\nWhen completing emulation of instruction that generated a userspace exit\\nfor I/O, don\u0027t recheck L1 intercepts as KVM has already finished that\\nphase of instruction execution, i.e. has already committed to allowing L2\\nto perform I/O.  If L1 (or host userspace) modifies the I/O permission\\nbitmaps during the exit to userspace,  KVM will treat the access as being\\nintercepted despite already having emulated the I/O access.\\n\\nPivot on EMULTYPE_NO_DECODE to detect that KVM is completing emulation.\\nOf the three users of EMULTYPE_NO_DECODE, only complete_emulated_io() (the\\nintended \\\"recipient\\\") can reach the code in question.  gp_interception()\u0027s\\nuse is mutually exclusive with is_guest_mode(), and\\ncomplete_emulated_insn_gp() unconditionally pairs EMULTYPE_NO_DECODE with\\nEMULTYPE_SKIP.\\n\\nThe bad behavior was detected by a syzkaller program that toggles port I/O\\ninterception during the userspace I/O exit, ultimately resulting in a WARN\\non vcpu-\u003earch.pio.count being non-zero due to KVM no completing emulation\\nof the I/O instruction.\\n\\n  WARNING: CPU: 23 PID: 1083 at arch/x86/kvm/x86.c:8039 emulator_pio_in_out+0x154/0x170 [kvm]\\n  Modules linked in: kvm_intel kvm irqbypass\\n  CPU: 23 UID: 1000 PID: 1083 Comm: repro Not tainted 6.16.0-rc5-c1610d2d66b1-next-vm #74 NONE\\n  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\\n  RIP: 0010:emulator_pio_in_out+0x154/0x170 [kvm]\\n  PKRU: 55555554\\n  Call Trace:\\n   \u003cTASK\u003e\\n   kvm_fast_pio+0xd6/0x1d0 [kvm]\\n   vmx_handle_exit+0x149/0x610 [kvm_intel]\\n   kvm_arch_vcpu_ioctl_run+0xda8/0x1ac0 [kvm]\\n   kvm_vcpu_ioctl+0x244/0x8c0 [kvm]\\n   __x64_sys_ioctl+0x8a/0xd0\\n   do_syscall_64+0x5d/0xc60\\n   entry_SYSCALL_64_after_hwframe+0x4b/0x53\\n   \u003c/TASK\u003e\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/00338255bb1f422642fb2798ebe92e93b6e4209b\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/3a062a5c55adc5507600b9ae6d911e247e2f1d6e\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/3d3abf3f7e8b1abb082070a343de82d7efc80523\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/7366830642505683bbe905a2ba5d18d6e4b512b8\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/a908eca437789589dd4624da428614c1275064dc\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/ba35a5d775799ce5ad60230be97336f2fefd518e\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/e0ce3ed1048a47986d15aef1a98ebda25560d257\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/e7177c7e32cb806f348387b7f4faafd4a5b32054\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/e750f85391286a4c8100275516973324b621a269\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
  }
}


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