CVE-2026-89903LoongArch: Do not save/restore percpu base register in rethook trampoline
- 7.8HighCVSS base score
- 0.18%Exploitation in 30 daysEPSS · top 93% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
Description
In the Linux kernel, the following vulnerability has been resolved: LoongArch: Do not save/restore percpu base register in rethook trampoline The rethook trampoline saves $r21 ($u0), the percpu base, into its frame at entry and restores it at exit. Inbetween rethook_trampoline_handler() may schedule via preempt_enable_notrace(). If the task migrates to another CPU, the frame's $r21 holds the old CPU's percpu base, and restoring it poisons $r21 on the new CPU. Until the next user->kernel transition heals $r21, all this_cpu_*() accesses (runqueues, RCU per-CPU data, timer tick programming, FPU ownership) hit the wrong CPU's percpu area. Under kretprobe-heavy preemptible load this can corrupt scheduler and timer state: scheduling-while-atomic splats, wrong-CPU RCU warnings, WARN_ON_ONCE(rq != this_rq()) in nohz_balance_exit_idle(), and CPUs parking in the idle loop with the constant timer never re-armed (hard lockup). Reproduces on a Loongson-3A6000 with kretprobes on VFS paths plus heavy file churn (OS install / unsquashfs). By convention $r21 always holds the current CPU's percpu base in kernel mode: SAVE_SOME() at exception entry reloads it only when coming from user mode, and RESTORE_SOME() restores it only when returning to user mode; the context-switch path never writes it. Therefore the live $r21 at trampoline exit is already correct, and nothing inbetween can change it legitimately (kernel C code cannot write a global register variable). The same flaw existed even in the pre-rethook kretprobe trampoline since v6.3; it was carried over when rethook replaced it. Drop both the save and the restore here. Drop the restore is enough to solve the issue, and drop the save is to keep the code tidy and no need to clear it.
Timeline
ID reserved
By Linux
- 5 days later
· 5 days later
Published
- 33 days later
· 33 days later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| LinuxCNA (assigner) | 3.1 | High7.8 | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H |
| NVDNVD · Received | 3.1 | High7.8 | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H |
- EPSS (exploitation in 30 days)
- 0.18% · top 93% of all CVEs (12 Nov 2026)
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.8.
Affected products
- affected 3f5536860086d906b01ec5ed68cf50c7edcc40af – < a03b5e7483ad2c33ba5dd2adb8552e84bfee8fe2
- affected 3f5536860086d906b01ec5ed68cf50c7edcc40af – < 8f15e95b438bc6b3c9f23a33c9a0d0678ebd1dc8
- affected 3f5536860086d906b01ec5ed68cf50c7edcc40af – < 266ffc92e68593759adfe3d58f188773d32782c3
- affected 3f5536860086d906b01ec5ed68cf50c7edcc40af – < c048b0a3c0836c4b1bef4b51d355d27090bf6790
- affected 3f5536860086d906b01ec5ed68cf50c7edcc40af – < c3f2feace5e4f4b01b68b9f947b19adb4155c32e
- affected 6.3
- unaffected < 6.3
- unaffected 6.6.157 – ≤ 6.6.*
- unaffected 6.12.110 – ≤ 6.12.*
- unaffected 6.18.51 – ≤ 6.18.*
- unaffected 7.2.5 – ≤ 7.2.*
- unaffected 7.3 – ≤ *
References
References5
- https://git.kernel.org/stable/c/a03b5e7483ad2c33ba5dd2adb8552e84bfee8fe2 (opens in a new tab)
- https://git.kernel.org/stable/c/8f15e95b438bc6b3c9f23a33c9a0d0678ebd1dc8 (opens in a new tab)
- https://git.kernel.org/stable/c/266ffc92e68593759adfe3d58f188773d32782c3 (opens in a new tab)
- https://git.kernel.org/stable/c/c048b0a3c0836c4b1bef4b51d355d27090bf6790 (opens in a new tab)
- https://git.kernel.org/stable/c/c3f2feace5e4f4b01b68b9f947b19adb4155c32e (opens in a new tab)
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-2026-80503 (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
[](https://cveledger.app/cve/CVE-2026-89903)Record last updated .