CVE-2025-68211ksm: use range-walk function to jump over holes in scan_get_next_rmap_item

Description

In the Linux kernel, the following vulnerability has been resolved: ksm: use range-walk function to jump over holes in scan_get_next_rmap_item Currently, scan_get_next_rmap_item() walks every page address in a VMA to locate mergeable pages. This becomes highly inefficient when scanning large virtual memory areas that contain mostly unmapped regions, causing ksmd to use large amount of cpu without deduplicating much pages. This patch replaces the per-address lookup with a range walk using walk_page_range(). The range walker allows KSM to skip over entire unmapped holes in a VMA, avoiding unnecessary lookups. This problem was previously discussed in [1]. Consider the following test program which creates a 32 TiB mapping in the virtual address space but only populates a single page: #include <unistd.h> #include <stdio.h> #include <sys/mman.h> /* 32 TiB */ const size_t size = 32ul * 1024 * 1024 * 1024 * 1024; int main() { char *area = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_NORESERVE | MAP_PRIVATE | MAP_ANON, -1, 0); if (area == MAP_FAILED) { perror("mmap() failed\n"); return -1; } /* Populate a single page such that we get an anon_vma. */ *area = 0; /* Enable KSM. */ madvise(area, size, MADV_MERGEABLE); pause(); return 0; } $ ./ksm-sparse & $ echo 1 > /sys/kernel/mm/ksm/run Without this patch ksmd uses 100% of the cpu for a long time (more then 1 hour in my test machine) scanning all the 32 TiB virtual address space that contain only one mapped page. This makes ksmd essentially deadlocked not able to deduplicate anything of value. With this patch ksmd walks only the one mapped page and skips the rest of the 32 TiB virtual address space, making the scan fast using little cpu.

Timeline

Scores

EPSS (exploitation in 30 days)

0.15% · top 96% of all CVEs (14 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: no · Technical impact: partial

The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.5.

Affected products

• Linux · Linux

  • affected 31dbd01f314364b70c2e026a5793a29a4da8a9dc – < 220cb3e425e17587f560335924cba9f16a842c64
  • affected 31dbd01f314364b70c2e026a5793a29a4da8a9dc – < 10644e8839544dd5699c03c8fb1aeeefc41602fd
  • affected 31dbd01f314364b70c2e026a5793a29a4da8a9dc – < 67137b715b7db28d82e4ed07a7092c2fa6ba7adb
  • affected 31dbd01f314364b70c2e026a5793a29a4da8a9dc – < 9c2f8a9b68024e5ebb4813665845ec0a95f2eac3
  • affected 31dbd01f314364b70c2e026a5793a29a4da8a9dc – < 74f78421c925b6d17695566f0c5941de57fd44b3
  • affected 31dbd01f314364b70c2e026a5793a29a4da8a9dc – < f62973e0767e4fcd6799087787fca08ca2a85b8c
  • affected 31dbd01f314364b70c2e026a5793a29a4da8a9dc – < f5548c318d6520d4fa3c5ed6003eeb710763cbc5

• Linux · Linux

  • affected 2.6.32
  • unaffected < 2.6.32
  • unaffected 5.10.249 – ≤ 5.10.*
  • unaffected 5.15.199 – ≤ 5.15.*
  • unaffected 6.1.161 – ≤ 6.1.*
  • unaffected 6.6.121 – ≤ 6.6.*
  • unaffected 6.12.59 – ≤ 6.12.*
  • unaffected 6.17.9 – ≤ 6.17.*
  • unaffected 6.18 – ≤ *

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• EUVD EUVD-2025-203685 (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2025-68211](https://cveledger.app/badge/CVE-2025-68211.svg)](https://cveledger.app/cve/CVE-2025-68211)

Record last updated 11 Jun 2026, 18:44 UTC.