CVE-2026-89903

/// Technical 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 h

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References