GHSA-J7CP-5J3G-7Q5W
Vulnerability from github – Published: 2026-04-22 15:31 – Updated: 2026-04-22 15:31In the Linux kernel, the following vulnerability has been resolved:
mm/huge_memory: fix folio isn't locked in softleaf_to_folio()
On arm64 server, we found folio that get from migration entry isn't locked in softleaf_to_folio(). This issue triggers when mTHP splitting and zap_nonpresent_ptes() races, and the root cause is lack of memory barrier in softleaf_to_folio(). The race is as follows:
CPU0 CPU1
deferred_split_scan() zap_nonpresent_ptes() lock folio split_folio() unmap_folio() change ptes to migration entries __split_folio_to_order() softleaf_to_folio() set flags(including PG_locked) for tail pages folio = pfn_folio(softleaf_to_pfn(entry)) smp_wmb() VM_WARN_ON_ONCE(!folio_test_locked(folio)) prep_compound_page() for tail pages
In __split_folio_to_order(), smp_wmb() guarantees page flags of tail pages are visible before the tail page becomes non-compound. smp_wmb() should be paired with smp_rmb() in softleaf_to_folio(), which is missed. As a result, if zap_nonpresent_ptes() accesses migration entry that stores tail pfn, softleaf_to_folio() may see the updated compound_head of tail page before page->flags.
This issue will trigger VM_WARN_ON_ONCE() in pfn_swap_entry_folio() because of the race between folio split and zap_nonpresent_ptes() leading to a folio incorrectly undergoing modification without a folio lock being held.
This is a BUG_ON() before commit 93976a20345b ("mm: eliminate further swapops predicates"), which in merged in v6.19-rc1.
To fix it, add missing smp_rmb() if the softleaf entry is migration entry in softleaf_to_folio() and softleaf_to_page().
[tujinjiang@huawei.com: update function name and comments]
{
"affected": [],
"aliases": [
"CVE-2026-31466"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-04-22T14:16:42Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm/huge_memory: fix folio isn\u0027t locked in softleaf_to_folio()\n\nOn arm64 server, we found folio that get from migration entry isn\u0027t locked\nin softleaf_to_folio(). This issue triggers when mTHP splitting and\nzap_nonpresent_ptes() races, and the root cause is lack of memory barrier\nin softleaf_to_folio(). The race is as follows:\n\n\tCPU0 CPU1\n\ndeferred_split_scan() zap_nonpresent_ptes()\n lock folio\n split_folio()\n unmap_folio()\n change ptes to migration entries\n __split_folio_to_order() softleaf_to_folio()\n set flags(including PG_locked) for tail pages folio = pfn_folio(softleaf_to_pfn(entry))\n smp_wmb() VM_WARN_ON_ONCE(!folio_test_locked(folio))\n prep_compound_page() for tail pages\n\nIn __split_folio_to_order(), smp_wmb() guarantees page flags of tail pages\nare visible before the tail page becomes non-compound. smp_wmb() should\nbe paired with smp_rmb() in softleaf_to_folio(), which is missed. As a\nresult, if zap_nonpresent_ptes() accesses migration entry that stores tail\npfn, softleaf_to_folio() may see the updated compound_head of tail page\nbefore page-\u003eflags.\n\nThis issue will trigger VM_WARN_ON_ONCE() in pfn_swap_entry_folio()\nbecause of the race between folio split and zap_nonpresent_ptes()\nleading to a folio incorrectly undergoing modification without a folio\nlock being held.\n\nThis is a BUG_ON() before commit 93976a20345b (\"mm: eliminate further\nswapops predicates\"), which in merged in v6.19-rc1.\n\nTo fix it, add missing smp_rmb() if the softleaf entry is migration entry\nin softleaf_to_folio() and softleaf_to_page().\n\n[tujinjiang@huawei.com: update function name and comments]",
"id": "GHSA-j7cp-5j3g-7q5w",
"modified": "2026-04-22T15:31:42Z",
"published": "2026-04-22T15:31:42Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-31466"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/426ee10711586617da869c8bb798214965337617"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4c5e7f0fcd592801c9cc18f29f80fbee84eb8669"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/722cfaf6b31d31123439e67b5deac6b1261a3dea"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7ad1997b9bc8032603df8f091761114479285769"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7ddcf4a245c1c5a91fdd9698757e3d95179ffe41"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8bfb8414e9f2ce6f5f2f0e3d0da52f2d132128e7"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b8c49ad888892ad7b77062b9c102b799a3e9b4f8"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f1acf5887c2bbaf998dc3fe32c72b7a8b84a3ddd"
}
],
"schema_version": "1.4.0",
"severity": []
}
Sightings
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