Cloudanix VulnDB

CVE-2023-53859

None

CVSS

—

EPSS

0.2%

Published

Dec 9, 2025

CISA due date

—

Cloudanix analysis

Schedule a fix SSVC: Track

A Linux kernel bug on certain IBM mainframe systems can cause warning messages when the computer is idle and tracing is turned on, and updating the kernel fixes it.

Exploitation
Other
Attacker needs
None
Complexity
Theoretical
Impact
Other
Component
OS kernel
Class
Other
Remediation
Patch
Effort
Low
Patch risk
None

What it actually does

arch_cpu_idle() on s390 lacks noinstr annotation, allowing ftrace entry while RCU is not watching and triggering warnings in trace_recursion handling.

Why it matters to the business

s390 systems running affected kernels may experience spurious warnings or tracing-related instability during idle transitions; remediation urgency is low given the age and absence from KEV or ransomware campaigns.

How an attack unfolds

An attacker with local access enables ftrace or similar tracing; the kernel then invokes arch_cpu_idle() without RCU watching, hitting the new warning added in linux-next and potentially disrupting tracing or logging on the affected CPU.

How to fix it

Upgrade to a fixed kernel containing commit 49aa49952116b8fd56bfb1e8c69bce179f49bece; for leptonlib packages on Ubuntu Pro 18.04 apply 1.75.3-3ubuntu0.1~esm1 or later.

How to confirm the fix worked

Confirm kernel version contains the noinstr change for arch_cpu_idle(); re-enable tracing and verify absence of the RCU warning on s390 idle entry.

Typical attack path

  1. gain local access on s390 system
  2. enable ftrace or kernel tracing
  3. trigger CPU idle path
  4. observe RCU warning and potential trace corruption

How to detect it

review kernel logs for the exact RCU warning string and stack trace involving arch_cpu_idle and arch_ftrace_ops_list_func on s390 hardware.

What your security team should do

  • apply the referenced kernel commit or distribution update on all s390 systems
  • monitor EPSS trend and re-evaluate if new exploitation appears
  • test tracing workloads after patching to confirm warning is resolved

The record

In the Linux kernel, the following vulnerability has been resolved: s390/idle: mark arch_cpu_idle() noinstr linux-next commit ("cpuidle: tracing: Warn about !rcu_is_watching()") adds a new warning which hits on s390's arch_cpu_idle() function: RCU not on for: arch_cpu_idle+0x0/0x28 WARNING: CPU: 2 PID: 0 at include/linux/trace_recursion.h:162 arch_ftrace_ops_list_func+0x24c/0x258 Modules linked in: CPU: 2 PID: 0 Comm: swapper/2 Not tainted 6.2.0-rc6-next-20230202 #4 Hardware name: IBM 8561 T01 703 (z/VM 7.3.0) Krnl PSW : 0404d00180000000 00000000002b55c0 (arch_ftrace_ops_list_func+0x250/0x258) R:0 T:1 IO:0 EX:0 Key:0 M:1 W:0 P:0 AS:3 CC:1 PM:0 RI:0 EA:3 Krnl GPRS: c0000000ffffbfff 0000000080000002 0000000000000026 0000000000000000 0000037ffffe3a28 0000037ffffe3a20 0000000000000000 0000000000000000 0000000000000000 0000000000f4acf6 00000000001044f0 0000037ffffe3cb0 0000000000000000 0000000000000000 00000000002b55bc 0000037ffffe3bb8 Krnl Code: 00000000002b55b0: c02000840051 larl %r2,0000000001335652 00000000002b55b6: c0e5fff512d1 brasl %r14,0000000000157b58 #00000000002b55bc: af000000 mc 0,0 >00000000002b55c0: a7f4ffe7 brc 15,00000000002b558e 00000000002b55c4: 0707 bcr 0,%r7 00000000002b55c6: 0707 bcr 0,%r7 00000000002b55c8: eb6ff0480024 stmg %r6,%r15,72(%r15) 00000000002b55ce: b90400ef lgr %r14,%r15 Call Trace: [<00000000002b55c0>] arch_ftrace_ops_list_func+0x250/0x258 ([<00000000002b55bc>] arch_ftrace_ops_list_func+0x24c/0x258) [<0000000000f5f0fc>] ftrace_common+0x1c/0x20 [<00000000001044f6>] arch_cpu_idle+0x6/0x28 [<0000000000f4acf6>] default_idle_call+0x76/0x128 [<00000000001cc374>] do_idle+0xf4/0x1b0 [<00000000001cc6ce>] cpu_startup_entry+0x36/0x40 [<0000000000119d00>] smp_start_secondary+0x140/0x150 [<0000000000f5d2ae>] restart_int_handler+0x6e/0x90 Mark arch_cpu_idle() noinstr like all other architectures with CONFIG_ARCH_WANTS_NO_INSTR (should) have it to fix this.

Affected packages

Ecosystem Package Introduced Fixed
Linux Kernel 0 5.15.99
Linux Kernel 5.9.0 5.15.99

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