CVE-2026-93253
UnknownSummary
A vulnerability in the Linux kernel's CPU isolation (housekeeping) mechanism was found, where memblock-allocated memory for the CPU mask was freed too early during boot, before the memory map was fully initialized. This caused a warning and potential system malfunction when using the 'nohz_full' boot parameter. The fix defers freeing this memory until initcall processing.
Risk Assessment
The risk involves improper system behavior during boot with the nohz_full parameter, potentially leading to kernel warnings, memory errors, or system instability. Organizations using CPU isolation may experience performance issues or crashes.
Recommendation
It is recommended to update the Linux kernel to a version containing the fix (commit deferring memblock memory freeing to initcall). Also monitor kernel logs for memblock-related warnings during boot.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: sched/isolation: Defer freeing of cpumask memblock memory to initcall When testing a linux-next kernel with commit 59bd1d914bb5 ("memblock: warn when freeing reserved memory before memory map is initialized"), the following warning was hit when there was a "nohz_full" kernel boot parameter. Cannot free reserved memory because of deferred initialization of the memory map WARNING: mm/memblock.c:904 at __free_reserved_area+0xde/0xf0, CPU#0: swapper/0/0 : Call Trace: <TASK> memblock_phys_free+0xcb/0x100 housekeeping_init+0x14c/0x170 start_kernel+0x207/0x450 x86_64_start_reservations+0x24/0x30 x86_64_start_kernel+0xda/0xe0 common_startup_64+0x13e/0x141 </TASK> IOW, we shouldn't free memblock allocated memory so early in the boot process when memory map isn't fully initialized in deferred_init_memmap(). Fix it by saving the housekeeping cpumask memblock memory to be freed into a llist free list in housekeeping_init() and add a new housekeeping_late_init() helper to defer the actual freeing of memblock memory to when initcall's are being processed. The cpumask memblock memory is treated as a llist_node with the size of a "long" type which is also smallest cpumask size that can be allocated. The non-atomic version of the llist APIs are used as there is no contention. This commit depends on the presence of commit 7c2eee9c1367 ("memblock: don't touch memblock arrays when memblock_free() is called late") to prevent a KASAN UAF bug report [1]. [1] https://lore.kernel.org/lkml/[email protected]/
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

