CVE-2022-48845 MIPS: smp: fill in sibling and core maps earlier

Medium 5.5 Published 16 Jul 2024 Updated 11 May 2026

A null pointer dereference in the Linux kernel MIPS SMP code causes a warning and potential crash when CONFIG_SCHED_CORE is enabled.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2022-48845?

CVE-2022-48845 is a medium-severity vulnerability in Linux kernel, published on 16 Jul 2024. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

In the Linux kernel, the following vulnerability has been resolved:

MIPS: smp: fill in sibling and core maps earlier

After enabling CONFIG_SCHED_CORE (landed during 5.14 cycle), 2-core 2-thread-per-core interAptiv (CPS-driven) started emitting the following:

[ 0.025698] CPU1 revision is: 0001a120 (MIPS interAptiv (multi)) [ 0.048183] ------------[ cut here ]------------ [ 0.048187] WARNING: CPU: 1 PID: 0 at kernel/sched/core.c:6025 sched_core_cpu_starting+0x198/0x240 [ 0.048220] Modules linked in: [ 0.048233] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.17.0-rc3+ #35 b7b319f24073fd9a3c2aa7ad15fb7993eec0b26f [ 0.048247] Stack : 817f0000 00000004 327804c8 810eb050 00000000 00000004 00000000 c314fdd1 [ 0.048278] 830cbd64 819c0000 81800000 817f0000 83070bf4 00000001 830cbd08 00000000 [ 0.048307] 00000000 00000000 815fcbc4 00000000 00000000 00000000 00000000 00000000 [ 0.048334] 00000000 00000000 00000000 00000000 817f0000 00000000 00000000 817f6f34 [ 0.048361] 817f0000 818a3c00 817f0000 00000004 00000000 00000000 4dc33260 0018c933 [ 0.048389] ... [ 0.048396] Call Trace: [ 0.048399] [<8105a7bc>] show_stack+0x3c/0x140 [ 0.048424] [<8131c2a0>] dump_stack_lvl+0x60/0x80 [ 0.048440] [<8108b5c0>] __warn+0xc0/0xf4 [ 0.048454] [<8108b658>] warn_slowpath_fmt+0x64/0x10c [ 0.048467] [<810bd418>] sched_core_cpu_starting+0x198/0x240 [ 0.048483] [<810c6514>] sched_cpu_starting+0x14/0x80 [ 0.048497] [<8108c0f8>] cpuhp_invoke_callback_range+0x78/0x140 [ 0.048510] [<8108d914>] notify_cpu_starting+0x94/0x140 [ 0.048523] [<8106593c>] start_secondary+0xbc/0x280 [ 0.048539] [ 0.048543] ---[ end trace 0000000000000000 ]--- [ 0.048636] Synchronize counters for CPU 1: done.

...for each but CPU 0/boot. Basic debug printks right before the mentioned line say:

[ 0.048170] CPU: 1, smt_mask:

So smt_mask, which is sibling mask obviously, is empty when entering the function. This is critical, as sched_core_cpu_starting() calculates core-scheduling parameters only once per CPU start, and it's crucial to have all the parameters filled in at that moment (at least it uses cpu_smt_mask() which in fact is `&cpu_sibling_map[cpu]` on MIPS).

A bit of debugging led me to that set_cpu_sibling_map() performing the actual map calculation, was being invocated after notify_cpu_start(), and exactly the latter function starts CPU HP callback round (sched_core_cpu_starting() is basically a CPU HP callback). While the flow is same on ARM64 (maps after the notifier, although before calling set_cpu_online()), x86 started calculating sibling maps earlier than starting the CPU HP callbacks in Linux 4.14 (see [0] for the reference). Neither me nor my brief tests couldn't find any potential caveats in calculating the maps right after performing delay calibration, but the WARN splat is now gone. The very same debug prints now yield exactly what I expected from them:

[ 0.048433] CPU: 1, smt_mask: 0-1

[0] https://git.kernel.org/pub/scm/linux/kernel/git/mips/linux.git/commit/?id=76ce7cfe35ef

Which versions are affected by CVE-2022-48845?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2022-48845?

Apply the vendor's patch.

Is CVE-2022-48845 being exploited?

There is no known exploitation of CVE-2022-48845 in the wild and no public exploit code.

All Linux kernel vulnerabilities

Sources

Also known as DEBIAN-CVE-2022-48845, GHSA-r7cx-6c4p-88r8, UBUNTU-CVE-2022-48845.