CVE-2023-52831

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 WARNON() when rebuilding the scheduler domains and a subsequent panic due to and unhandled empty CPU mas in partitionscheddomainslocked().

cpusethotplugworkfn() rebuildscheddomainslocked() ndoms = generatescheddomains(&doms, &attr); cpumaskand(doms[0], topcpuset.effectivecpus, housekeepingcpumask(HKFLAG_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 buildscheddomains+0x120c/0x1408 Call trace: buildscheddomains+0x120c/0x1408 partitionscheddomainslocked+0x234/0x880 rebuildscheddomainslocked+0x37c/0x798 rebuildscheddomains+0x30/0x58 cpusethotplugworkfn+0x2a8/0x930

Unable to handle kernel paging request at virtual address fffe80027ab37080 partitionscheddomainslocked+0x318/0x880 rebuildscheddomainslocked+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.