TLDRVuln - Cybersecurity Vulnerabilities Made Simple

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.