Vulnerability-Lookup

GHSA-6VP7-HJ7X-73JJ

Vulnerability from github – Published: 2026-10-23 15:31 – Updated: 2026-10-23 15:31

Details

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

x86/mm: Drop unnecessary PMD page copy when freeing

On a box with a discrete GPU, lockdep reports a possible deadlock as soon as kswapd shrinks the TTM page pool. The immediate cause is an x86 commit that added an mmap_read_lock() to kernel page protection munging code.

The huge vmap code holds the same lock over a GFP_KERNEL allocation, which is a no-no now that reclaim can take it. That allocation is in a page table free path and ends up being for dubious purposes[1]. Basically, it tries to avoid hardware setting Accessed=1 in page table entries that are unreachable by the hardware, a non-issue.

Remove the PMD copy. Detach the original PMD page at the PUD, flush the mid-level caches, and free the PTE tables straight from the detached PMD page. With no allocation left, the locking issue is gone.

Lockdep splat/analysis:

WARNING: possible circular locking dependency detected 7.3.0-rc3-f6e7b42bf05b+ #183 Tainted: G U

kswapd0/269 is trying to acquire lock: ((init_mm).mmap_lock){++++}-{4:4}, at: change_page_attr_set_clr+0x29a/0x4a0 but task is already holding lock: (pool_shrink_rwsem){.+.+}-{4:4}, at: ttm_pool_shrink+0xb2/0x330 [ttm] Chain exists of: (init_mm).mmap_lock --> fs_reclaim --> pool_shrink_rwsem

The cycle is built from three edges:

1) pool_shrink_rwsem -> (init_mm).mmap_lock

 The TTM shrinker restores the caching attribute of every page it
 frees, while holding pool_shrink_rwsem:

   ttm_pool_shrink()
   -> ttm_pool_dispose_list()
   -> ttm_pool_free_page()
   -> set_pages_wb()
   -> change_page_attr_set_clr()   [ init_mm mmap read lock ]

2) fs_reclaim -> pool_shrink_rwsem

 The same shrinker, called from reclaim.

3) (init_mm).mmap_lock -> fs_reclaim

 ioremap() installing a huge PUD mapping over an existing PMD table:

   ioremap_page_range()
   -> vmap_range_noflush()
   -> vmap_try_huge_pud()          [ init_mm mmap read lock ]
   -> pud_free_pmd_page()
   -> __get_free_page(GFP_KERNEL)  [ enters reclaim ]

[ dhansen: Lots of changelog munging/trimming and merged comments from my version of the fix. ]

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{
  "affected": [],
  "aliases": [
    "CVE-2026-98939"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-23T13:17:14Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/mm: Drop unnecessary PMD page copy when freeing\n\nOn a box with a discrete GPU, lockdep reports a possible deadlock as\nsoon as kswapd shrinks the TTM page pool. The immediate cause is an\nx86 commit that added an mmap_read_lock() to kernel page protection\nmunging code.\n\nThe huge vmap code holds the same lock over a GFP_KERNEL allocation,\nwhich is a no-no now that reclaim can take it. That allocation is in a\npage table *free* path and ends up being for dubious purposes[1].\nBasically, it tries to avoid hardware setting Accessed=1 in page table\nentries that are unreachable by the hardware, a non-issue.\n\nRemove the PMD copy. Detach the original PMD page at the PUD, flush\nthe mid-level caches, and free the PTE tables straight from the\ndetached PMD page. With no allocation left, the locking issue is gone.\n\nLockdep splat/analysis:\n\n  WARNING: possible circular locking dependency detected\n  7.3.0-rc3-f6e7b42bf05b+ #183 Tainted: G     U\n  ------------------------------------------------------\n  kswapd0/269 is trying to acquire lock:\n  ((init_mm).mmap_lock){++++}-{4:4}, at: change_page_attr_set_clr+0x29a/0x4a0\n  but task is already holding lock:\n  (pool_shrink_rwsem){.+.+}-{4:4}, at: ttm_pool_shrink+0xb2/0x330 [ttm]\n  Chain exists of:\n    (init_mm).mmap_lock --\u003e fs_reclaim --\u003e pool_shrink_rwsem\n\nThe cycle is built from three edges:\n\n  1) pool_shrink_rwsem -\u003e (init_mm).mmap_lock\n\n     The TTM shrinker restores the caching attribute of every page it\n     frees, while holding pool_shrink_rwsem:\n\n       ttm_pool_shrink()\n       -\u003e ttm_pool_dispose_list()\n       -\u003e ttm_pool_free_page()\n       -\u003e set_pages_wb()\n       -\u003e change_page_attr_set_clr()   [ init_mm mmap read lock ]\n\n  2) fs_reclaim -\u003e pool_shrink_rwsem\n\n     The same shrinker, called from reclaim.\n\n  3) (init_mm).mmap_lock -\u003e fs_reclaim\n\n     ioremap() installing a huge PUD mapping over an existing PMD table:\n\n       ioremap_page_range()\n       -\u003e vmap_range_noflush()\n       -\u003e vmap_try_huge_pud()          [ init_mm mmap read lock ]\n       -\u003e pud_free_pmd_page()\n       -\u003e __get_free_page(GFP_KERNEL)  [ enters reclaim ]\n\n[ dhansen: Lots of changelog munging/trimming and merged comments from my\n\t   version of the fix. ]",
  "id": "GHSA-6vp7-hj7x-73jj",
  "modified": "2026-10-23T15:31:31Z",
  "published": "2026-10-23T15:31:31Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98939"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d3c2d2692bdf4af94bb27bc7a3aa0a348a567606"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e3ee38c1bc0b11a8d3e63dce7050759b61864286"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f38c57a28ebbd057471573e39555d5aa11ab03cf"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

CVE-2026-98939 (GCVE-0-2026-98939)

Vulnerability from cvelistv5 – Published: 2026-10-23 12:12 – Updated: 2026-10-23 12:12

Title

x86/mm: Drop unnecessary PMD page copy when freeing

Summary

In the Linux kernel, the following vulnerability has been resolved: x86/mm: Drop unnecessary PMD page copy when freeing On a box with a discrete GPU, lockdep reports a possible deadlock as soon as kswapd shrinks the TTM page pool. The immediate cause is an x86 commit that added an mmap_read_lock() to kernel page protection munging code. The huge vmap code holds the same lock over a GFP_KERNEL allocation, which is a no-no now that reclaim can take it. That allocation is in a page table *free* path and ends up being for dubious purposes[1]. Basically, it tries to avoid hardware setting Accessed=1 in page table entries that are unreachable by the hardware, a non-issue. Remove the PMD copy. Detach the original PMD page at the PUD, flush the mid-level caches, and free the PTE tables straight from the detached PMD page. With no allocation left, the locking issue is gone. Lockdep splat/analysis: WARNING: possible circular locking dependency detected 7.3.0-rc3-f6e7b42bf05b+ #183 Tainted: G U ------------------------------------------------------ kswapd0/269 is trying to acquire lock: ((init_mm).mmap_lock){++++}-{4:4}, at: change_page_attr_set_clr+0x29a/0x4a0 but task is already holding lock: (pool_shrink_rwsem){.+.+}-{4:4}, at: ttm_pool_shrink+0xb2/0x330 [ttm] Chain exists of: (init_mm).mmap_lock --> fs_reclaim --> pool_shrink_rwsem The cycle is built from three edges: 1) pool_shrink_rwsem -> (init_mm).mmap_lock The TTM shrinker restores the caching attribute of every page it frees, while holding pool_shrink_rwsem: ttm_pool_shrink() -> ttm_pool_dispose_list() -> ttm_pool_free_page() -> set_pages_wb() -> change_page_attr_set_clr() [ init_mm mmap read lock ] 2) fs_reclaim -> pool_shrink_rwsem The same shrinker, called from reclaim. 3) (init_mm).mmap_lock -> fs_reclaim ioremap() installing a huge PUD mapping over an existing PMD table: ioremap_page_range() -> vmap_range_noflush() -> vmap_try_huge_pud() [ init_mm mmap read lock ] -> pud_free_pmd_page() -> __get_free_page(GFP_KERNEL) [ enters reclaim ] [ dhansen: Lots of changelog munging/trimming and merged comments from my version of the fix. ]

Severity

No CVSS data available.

Assigner

Linux CNA under the mitre root

CNA scorecard D 53/100 over 7067 records in the last 180 days details

References

3 references

URL	Tags
https://git.kernel.org/stable/c/d3c2d2692bdf4af94…
https://git.kernel.org/stable/c/f38c57a28ebbd0574…
https://git.kernel.org/stable/c/e3ee38c1bc0b11a8d…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: e21a9ea81426a85fdb0cdcfcc99d5d9c16b402ab , < d3c2d2692bdf4af94bb27bc7a3aa0a348a567606 (git) Affected: cc73b2043d106b467accd38e9b1fc09e0607c056 , < f38c57a28ebbd057471573e39555d5aa11ab03cf (git) Affected: d5d8b8662e6e5a565b47a0388640e88402f23274 , < e3ee38c1bc0b11a8d3e63dce7050759b61864286 (git)
Linux	Linux	Affected: 6.18.53 , < 6.18.56 (semver) Affected: 7.2.7 , < 7.2.10 (semver)

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "arch/x86/mm/pgtable.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
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              "status": "affected",
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              "versionType": "git"
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            {
              "lessThan": "f38c57a28ebbd057471573e39555d5aa11ab03cf",
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              "version": "cc73b2043d106b467accd38e9b1fc09e0607c056",
              "versionType": "git"
            },
            {
              "lessThan": "e3ee38c1bc0b11a8d3e63dce7050759b61864286",
              "status": "affected",
              "version": "d5d8b8662e6e5a565b47a0388640e88402f23274",
              "versionType": "git"
            }
          ]
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          "vendor": "Linux",
          "versions": [
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              "lessThan": "6.18.56",
              "status": "affected",
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              "versionType": "semver"
            },
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              "status": "affected",
              "version": "7.2.7",
              "versionType": "semver"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "versionStartIncluding": "6.18.53",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/mm: Drop unnecessary PMD page copy when freeing\n\nOn a box with a discrete GPU, lockdep reports a possible deadlock as\nsoon as kswapd shrinks the TTM page pool. The immediate cause is an\nx86 commit that added an mmap_read_lock() to kernel page protection\nmunging code.\n\nThe huge vmap code holds the same lock over a GFP_KERNEL allocation,\nwhich is a no-no now that reclaim can take it. That allocation is in a\npage table *free* path and ends up being for dubious purposes[1].\nBasically, it tries to avoid hardware setting Accessed=1 in page table\nentries that are unreachable by the hardware, a non-issue.\n\nRemove the PMD copy. Detach the original PMD page at the PUD, flush\nthe mid-level caches, and free the PTE tables straight from the\ndetached PMD page. With no allocation left, the locking issue is gone.\n\nLockdep splat/analysis:\n\n  WARNING: possible circular locking dependency detected\n  7.3.0-rc3-f6e7b42bf05b+ #183 Tainted: G     U\n  ------------------------------------------------------\n  kswapd0/269 is trying to acquire lock:\n  ((init_mm).mmap_lock){++++}-{4:4}, at: change_page_attr_set_clr+0x29a/0x4a0\n  but task is already holding lock:\n  (pool_shrink_rwsem){.+.+}-{4:4}, at: ttm_pool_shrink+0xb2/0x330 [ttm]\n  Chain exists of:\n    (init_mm).mmap_lock --\u003e fs_reclaim --\u003e pool_shrink_rwsem\n\nThe cycle is built from three edges:\n\n  1) pool_shrink_rwsem -\u003e (init_mm).mmap_lock\n\n     The TTM shrinker restores the caching attribute of every page it\n     frees, while holding pool_shrink_rwsem:\n\n       ttm_pool_shrink()\n       -\u003e ttm_pool_dispose_list()\n       -\u003e ttm_pool_free_page()\n       -\u003e set_pages_wb()\n       -\u003e change_page_attr_set_clr()   [ init_mm mmap read lock ]\n\n  2) fs_reclaim -\u003e pool_shrink_rwsem\n\n     The same shrinker, called from reclaim.\n\n  3) (init_mm).mmap_lock -\u003e fs_reclaim\n\n     ioremap() installing a huge PUD mapping over an existing PMD table:\n\n       ioremap_page_range()\n       -\u003e vmap_range_noflush()\n       -\u003e vmap_try_huge_pud()          [ init_mm mmap read lock ]\n       -\u003e pud_free_pmd_page()\n       -\u003e __get_free_page(GFP_KERNEL)  [ enters reclaim ]\n\n[ dhansen: Lots of changelog munging/trimming and merged comments from my\n\t   version of the fix. ]"
        }
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      "providerMetadata": {
        "dateUpdated": "2026-10-23T12:12:06.180Z",
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    "datePublished": "2026-10-23T12:12:06.180Z",
    "dateReserved": "2026-09-25T10:25:14.381Z",
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    "state": "PUBLISHED"
  },
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}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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Confirmed: The vulnerability has been validated from an analyst's perspective.
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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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