CVE-2026-63807 (GCVE-0-2026-63807)
Vulnerability from cvelistv5
Published
2026-07-19 12:02
Modified
2026-08-17 04:51
Severity ?
8.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: KVM: x86/mmu: Ensure hugepage is in by slot before checking max mapping level When recovering hugepages in the shadow MMU, verify that the base gfn of the shadow page is actually contained within the target memslot, *before* querying the max mapping level given the shadow page's gfn. Failure to pre-check the validity of the gfn can lead to an out-of-bounds access to the slot's lpage_info (which typically manifests as a host #PF because the lpage_info is vmalloc'd) if the guest creates a hugepage mapping (in its PTEs) that extends "below" the bounds of a memslot. When faulting in memory for a guest, and the size of the guest mapping is greater than KVM's (current) max mapping, then KVM will create a "direct" shadow page (direct in that there are no gPTEs to shadow, and so the target gfn is a direct calculation given the base gfn of the shadow page). The hugepage recovery flow looks for such direct shadow pages, as forcing 4KiB mappings when dirty logging generates the guest > host mapping size case. When the 4KiB restriction is lifted, then KVM can replace the shadow page with a hugepage. But if KVM originally used a smaller mapping than the guest because the range of memory covered by the guest hugepage exceeds the bounds of a memslot, then KVM will link a direct shadow page with a gfn that is outside the bounds of the memslot being used to fault in memory. The rmap entry added for the leaf mapping is correct and within bounds, but the gfn of the leaf SPTE's parent shadow page will be out of bounds. BUG: unable to handle page fault for address: ffffc90000806ffc #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 100000067 P4D 100000067 PUD 1002a7067 PMD 10612f067 PTE 0 Oops: Oops: 0000 [#1] SMP CPU: 13 UID: 1000 PID: 757 Comm: mmu_stress_test Not tainted 7.1.0-rc1-48ce1e26eace-x86_pir_to_irr_comments-vm #341 PREEMPT Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:kvm_mmu_max_mapping_level+0x79/0x2b0 [kvm] Call Trace: <TASK> kvm_mmu_recover_huge_pages+0x21b/0x320 [kvm] kvm_set_memslot+0x1ee/0x590 [kvm] kvm_set_memory_region.part.0+0x3a1/0x4d0 [kvm] kvm_vm_ioctl+0x9bf/0x15d0 [kvm] __x64_sys_ioctl+0x8a/0xd0 do_syscall_64+0xb7/0xbb0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7f21c0f1a9bf </TASK> Don't bother pre-checking the bounds of the potential hugepage, i.e. don't check that e.g. sp->gfn + KVM_PAGES_PER_HPAGE(sp->role.level + 1) is also within the memslot, as the checks performed by kvm_mmu_max_mapping_level() are a superset of the basic bounds checks. I.e. pre-checking the full range would be a dubious micro-optimization.
References
Impacted products
Vendor Product Version
Linux Linux Version: 9eba50f8d7fcb61774f160890f98239fa3ab68a6
Version: 9eba50f8d7fcb61774f160890f98239fa3ab68a6
Version: 9eba50f8d7fcb61774f160890f98239fa3ab68a6
Version: 9eba50f8d7fcb61774f160890f98239fa3ab68a6
Version: 9eba50f8d7fcb61774f160890f98239fa3ab68a6
Version: 9eba50f8d7fcb61774f160890f98239fa3ab68a6
Version: 9eba50f8d7fcb61774f160890f98239fa3ab68a6
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "arch/x86/kvm/mmu/mmu.c",
            "include/linux/kvm_host.h"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "status": "affected",
              "version": "9eba50f8d7fcb61774f160890f98239fa3ab68a6",
              "versionType": "git"
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            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "arch/x86/kvm/mmu/mmu.c",
            "include/linux/kvm_host.h"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.12"
            },
            {
              "lessThan": "5.12",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.211",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.177",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.144",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.95",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.38",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.3",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.15.211",
                  "versionStartIncluding": "5.12",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.1.177",
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                  "vulnerable": true
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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/mmu: Ensure hugepage is in by slot before checking max mapping level\n\nWhen recovering hugepages in the shadow MMU, verify that the base gfn of\nthe shadow page is actually contained within the target memslot, *before*\nquerying the max mapping level given the shadow page\u0027s gfn.  Failure to\npre-check the validity of the gfn can lead to an out-of-bounds access to\nthe slot\u0027s lpage_info (which typically manifests as a host #PF because the\nlpage_info is vmalloc\u0027d) if the guest creates a hugepage mapping (in its\nPTEs) that extends \"below\" the bounds of a memslot.\n\nWhen faulting in memory for a guest, and the size of the guest mapping is\ngreater than KVM\u0027s (current) max mapping, then KVM will create a \"direct\"\nshadow page (direct in that there are no gPTEs to shadow, and so the target\ngfn is a direct calculation given the base gfn of the shadow page).  The\nhugepage recovery flow looks for such direct shadow pages, as forcing 4KiB\nmappings when dirty logging generates the guest \u003e host mapping size case.\nWhen the 4KiB restriction is lifted, then KVM can replace the shadow page\nwith a hugepage.\n\nBut if KVM originally used a smaller mapping than the guest because the\nrange of memory covered by the guest hugepage exceeds the bounds of a\nmemslot, then KVM will link a direct shadow page with a gfn that is outside\nthe bounds of the memslot being used to fault in memory.  The rmap entry\nadded for the leaf mapping is correct and within bounds, but the gfn of the\nleaf SPTE\u0027s parent shadow page will be out of bounds.\n\n  BUG: unable to handle page fault for address: ffffc90000806ffc\n  #PF: supervisor read access in kernel mode\n  #PF: error_code(0x0000) - not-present page\n  PGD 100000067 P4D 100000067 PUD 1002a7067 PMD 10612f067 PTE 0\n  Oops: Oops: 0000 [#1] SMP\n  CPU: 13 UID: 1000 PID: 757 Comm: mmu_stress_test Not tainted 7.1.0-rc1-48ce1e26eace-x86_pir_to_irr_comments-vm #341 PREEMPT\n  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\n  RIP: 0010:kvm_mmu_max_mapping_level+0x79/0x2b0 [kvm]\n  Call Trace:\n   \u003cTASK\u003e\n   kvm_mmu_recover_huge_pages+0x21b/0x320 [kvm]\n   kvm_set_memslot+0x1ee/0x590 [kvm]\n   kvm_set_memory_region.part.0+0x3a1/0x4d0 [kvm]\n   kvm_vm_ioctl+0x9bf/0x15d0 [kvm]\n   __x64_sys_ioctl+0x8a/0xd0\n   do_syscall_64+0xb7/0xbb0\n   entry_SYSCALL_64_after_hwframe+0x4b/0x53\n  RIP: 0033:0x7f21c0f1a9bf\n   \u003c/TASK\u003e\n\nDon\u0027t bother pre-checking the bounds of the potential hugepage, i.e. don\u0027t\ncheck that e.g. sp-\u003egfn + KVM_PAGES_PER_HPAGE(sp-\u003erole.level + 1) is also\nwithin the memslot, as the checks performed by kvm_mmu_max_mapping_level()\nare a superset of the basic bounds checks.  I.e. pre-checking the full\nrange would be a dubious micro-optimization."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The vulnerability is reached only through the KVM VM file descriptor ioctl path (KVM_SET_USER_MEMORY_REGION), which requires local syscall access to /dev/kvm rather than any network-facing protocol.\nAC:L - An attacker with KVM access can deterministically set up the required state (partial hugepage memslot, dirty logging enabled then disabled, guest hugepage mapping extending below slot bounds) and trigger the bug without depending on conditions outside their control.\nPR:L - Exploitation requires only local access to /dev/kvm and control of a VM (e.g., membership in the kvm group), as demonstrated by the reproducer running as UID 1000; it does not require host root in the init namespace.\nUI:N - No victim user interaction is required beyond the attacker issuing the KVM ioctl to disable dirty logging on a memslot they control.\nS:C - The vulnerable KVM x86 MMU code runs in the host kernel and a VM operator can corrupt or crash host kernel memory from their guest/VM management context, crossing the guest-to-host virtualization security boundary.\nC:H - The bug is an out-of-bounds kernel read of memslot lpage_info metadata via an invalid gfn index in kvm_mmu_max_mapping_level(), which per kernel guidance qualifies as high confidentiality impact even though it typically manifests as a page fault.\nI:H - Out-of-bounds access to kernel heap metadata in the KVM MMU subsystem can potentially be steered for memory corruption and control-flow influence; similar KVM shadow MMU memory safety bugs are scored at high integrity impact.\nA:H - The vulnerability reliably causes a host kernel oops/page fault (supervisor read to non-present vmalloc address) when triggered, constituting high availability impact via host kernel crash."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T04:51:13.303Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/7b52008023b7facf40fba3ebe92449bda8ea53b9"
        },
        {
          "url": "https://git.kernel.org/stable/c/5cab1c989f938f5e1b9a0de66486f1fc2c28479b"
        },
        {
          "url": "https://git.kernel.org/stable/c/48b91ed7e22bb82571c34f8b80b6ecdc90a6fab8"
        },
        {
          "url": "https://git.kernel.org/stable/c/c5c29b3c268332afe67d598a034c58344540ed92"
        },
        {
          "url": "https://git.kernel.org/stable/c/18587f9831612e24cd8f24be1ec15478feff7abc"
        },
        {
          "url": "https://git.kernel.org/stable/c/b2ae3245ea44dccaa9af676b6747476951883318"
        },
        {
          "url": "https://git.kernel.org/stable/c/ef057cbf825e03b63f6edf5980f96abf3c53089d"
        }
      ],
      "title": "KVM: x86/mmu: Ensure hugepage is in by slot before checking max mapping level",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-63807",
    "datePublished": "2026-07-19T12:02:10.759Z",
    "dateReserved": "2026-07-19T07:54:57.013Z",
    "dateUpdated": "2026-08-17T04:51:13.303Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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