Vulnerability CVE-2023-52831
Published: 2024-05-21

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

cpu/hotplug: Don't offline the last non-isolated CPU

If a system has isolated CPUs via the "isolcpus=" command line parameter,
then an attempt to offline the last housekeeping CPU will result in a
WARN_ON() when rebuilding the scheduler domains and a subsequent panic due
to and unhandled empty CPU mas in partition_sched_domains_locked().

cpuset_hotplug_workfn()
rebuild_sched_domains_locked()
ndoms = generate_sched_domains(&doms, &attr);
cpumask_and(doms[0], top_cpuset.effective_cpus, housekeeping_cpumask(HK_FLAG_DOMAIN));

Thus results in an empty CPU mask which triggers the warning and then the
subsequent crash:

WARNING: CPU: 4 PID: 80 at kernel/sched/topology.c:2366 build_sched_domains+0x120c/0x1408
Call trace:
build_sched_domains+0x120c/0x1408
partition_sched_domains_locked+0x234/0x880
rebuild_sched_domains_locked+0x37c/0x798
rebuild_sched_domains+0x30/0x58
cpuset_hotplug_workfn+0x2a8/0x930

Unable to handle kernel paging request at virtual address fffe80027ab37080
partition_sched_domains_locked+0x318/0x880
rebuild_sched_domains_locked+0x37c/0x798

Aside of the resulting crash, it does not make any sense to offline the last
last housekeeping CPU.

Prevent this by masking out the non-housekeeping CPUs when selecting a
target CPU for initiating the CPU unplug operation via the work queue.

 References:
https://git.kernel.org/stable/c/3410b702354702b500bde10e3cc1f9db8731d908
https://git.kernel.org/stable/c/335a47ed71e332c82339d1aec0c7f6caccfcda13
https://git.kernel.org/stable/c/3073f6df783d9d75f7f69f73e16c7ef85d6cfb63
https://git.kernel.org/stable/c/38685e2a0476127db766f81b1c06019ddc4c9ffa
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