{"cve":"CVE-2025-37964","nvd":{"published":"2025-05-20T16:15:34.683","modified":"2026-10-15T02:17:49.840","status":"Modified","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nx86/mm: Eliminate window where TLB flushes may be inadvertently skipped\n\ntl;dr: There is a window in the mm switching code where the new CR3 is\nset and the CPU should be getting TLB flushes for the new mm.  But\nshould_flush_tlb() has a bug and suppresses the flush.  Fix it by\nwidening the window where should_flush_tlb() sends an IPI.\n\nLong Version:\n\n=== History ===\n\nThere were a few things leading up to this.\n\nFirst, updating mm_cpumask() was observed to be too expensive, so it was\nmade lazier.  But being lazy caused too many unnecessary IPIs to CPUs\ndue to the now-lazy mm_cpumask().  So code was added to cull\nmm_cpumask() periodically[2].  But that culling was a bit too aggressive\nand skipped sending TLB flushes to CPUs that need them.  So here we are\nagain.\n\n=== Problem ===\n\nThe too-aggressive code in should_flush_tlb() strikes in this window:\n\n\t// Turn on IPIs for this CPU/mm combination, but only\n\t// if should_flush_tlb() agrees:\n\tcpumask_set_cpu(cpu, mm_cpumask(next));\n\n\tnext_tlb_gen = atomic64_read(&next->context.tlb_gen);\n\tchoose_new_asid(next, next_tlb_gen, &new_asid, &need_flush);\n\tload_new_mm_cr3(need_flush);\n\t// ^ After 'need_flush' is set to false, IPIs *MUST*\n\t// be sent to this CPU and not be ignored.\n\n        this_cpu_write(cpu_tlbstate.loaded_mm, next);\n\t// ^ Not until this point does should_flush_tlb()\n\t// become true!\n\nshould_flush_tlb() will suppress TLB flushes between load_new_mm_cr3()\nand writing to 'loaded_mm', which is a window where they should not be\nsuppressed.  Whoops.\n\n=== Solution ===\n\nThankfully, the fuzzy \"just about to write CR3\" window is already marked\nwith loaded_mm==LOADED_MM_SWITCHING.  Simply checking for that state in\nshould_flush_tlb() is sufficient to ensure that the CPU is targeted with\nan IPI.\n\nThis will cause more TLB flush IPIs.  But the window is relatively small\nand I do not expect this to cause any kind of measurable performance\nimpact.\n\nUpdate the comment where LOADED_MM_SWITCHING is written since it grew\nyet another user.\n\nPeter Z also raised a concern that should_flush_tlb() might not observe\n'loaded_mm' and 'is_lazy' in the same order that switch_mm_irqs_off()\nwrites them.  Add a barrier to ensure that they are observed in the\norder they are written.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","score":5.5},"cwes":[],"references":["https://git.kernel.org/stable/c/02ad4ce144bd27f71f583f667fdf3b3ba0753477","https://git.kernel.org/stable/c/12f703811af043d32b1c8a30001b2fa04d5cd0ac","https://git.kernel.org/stable/c/399ec9ca8fc4999e676ff89a90184ec40031cf59","https://git.kernel.org/stable/c/d41072906abec8bb8e01ed16afefbaa558908c89","https://git.kernel.org/stable/c/d87392094f96e162fa5fa5a8640d70cc0952806f"],"products":["debian:debian_linux","linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T22:01:57.636215869+00:00"},"epss":{"cve":"CVE-2025-37964","score":0.00209,"percentile":0.10988,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}