CVE-2025-37964

{"id": "CVE-2025-37964", "cveTags": [], "metrics": {"cvssMetricV31": [{"type": "Primary", "source": "nvd@nist.gov", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 5.5, "attackVector": "LOCAL", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "integrityImpact": "NONE", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "HIGH", "privilegesRequired": "LOW", "confidentialityImpact": "NONE"}, "impactScore": 3.6, "exploitabilityScore": 1.8}]}, "published": "2025-05-20T16:15:34.683", "references": [{"url": "https://git.kernel.org/stable/c/02ad4ce144bd27f71f583f667fdf3b3ba0753477", "tags": ["Patch"], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/12f703811af043d32b1c8a30001b2fa04d5cd0ac", "tags": ["Patch"], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/399ec9ca8fc4999e676ff89a90184ec40031cf59", "tags": ["Patch"], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/d41072906abec8bb8e01ed16afefbaa558908c89", "tags": ["Patch"], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/d87392094f96e162fa5fa5a8640d70cc0952806f", "tags": ["Patch"], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/fea4e317f9e7e1f449ce90dedc27a2d2a95bee5a", "tags": ["Patch"], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://lists.debian.org/debian-lts-announce/2025/08/msg00010.html", "tags": ["Third Party Advisory"], "source": "af854a3a-2127-422b-91ae-364da2661108"}], "vulnStatus": "Analyzed", "weaknesses": [{"type": "Primary", "source": "nvd@nist.gov", "description": [{"lang": "en", "value": "NVD-CWE-noinfo"}]}], "descriptions": [{"lang": "en", "value": "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."}, {"lang": "es", "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: x86/mm: Eliminar la ventana donde los vaciados de TLB pueden omitirse inadvertidamente tl;dr: Hay una ventana en el c\u00f3digo de conmutaci\u00f3n mm donde se establece el nuevo CR3 y la CPU deber\u00eda obtener vaciados de TLB para el nuevo mm. Pero should_flush_tlb() tiene un error y suprime el vaciado. Arr\u00e9glelo ampliando la ventana donde should_flush_tlb() env\u00eda una IPI. Versi\u00f3n larga: === Historial === Hubo algunas cosas que llevaron a esto. Primero, se observ\u00f3 que actualizar mm_cpumask() era demasiado costoso, por lo que se hizo m\u00e1s perezoso. Pero ser perezoso caus\u00f3 demasiados IPI innecesarios a las CPU debido al ahora perezoso mm_cpumask(). Entonces se agreg\u00f3 c\u00f3digo para descartar mm_cpumask() peri\u00f3dicamente[2]. Pero ese descarte fue demasiado agresivo y omiti\u00f3 el env\u00edo de vaciados de TLB a las CPU que los necesitan. As\u00ed que aqu\u00ed estamos de nuevo. === Problema === El c\u00f3digo demasiado agresivo en should_flush_tlb() ataca en esta ventana: // Activa las IPI para esta combinaci\u00f3n de CPU/mm, pero solo si should_flush_tlb() est\u00e1 de acuerdo: cpumask_set_cpu(cpu, mm_cpumask(next)); next_tlb_gen = atomic64_read(&next->context.tlb_gen); choose_new_asid(next, next_tlb_gen, &new_asid, &need_flush); load_new_mm_cr3(need_flush); // ^ Despu\u00e9s de que 'need_flush' se establece en falso, las IPI *DEBEN* // enviarse a esta CPU y no ignorarse. this_cpu_write(cpu_tlbstate.loaded_mm, next); // ^ \u00a1No es hasta este punto que should_flush_tlb() // se vuelve verdadero! should_flush_tlb() suprimir\u00e1 los vaciados de TLB entre load_new_mm_cr3() y la escritura en 'loaded_mm', que es una ventana donde no deber\u00edan suprimirse. \u00a1Uy! === Soluci\u00f3n === Afortunadamente, la ventana difusa \"a punto de escribir CR3\" ya est\u00e1 marcada con load_mm==LOADED_MM_SWITCHING. Simplemente comprobar ese estado en should_flush_tlb() es suficiente para asegurar que la CPU est\u00e9 dirigida a un IPI. Esto provocar\u00e1 m\u00e1s IPI de vaciado de TLB. Sin embargo, la ventana es relativamente peque\u00f1a y no preveo que esto tenga ning\u00fan impacto medible en el rendimiento. Actualice el comentario donde se escribe LOADED_MM_SWITCHING, ya que ha generado otro usuario. Peter Z tambi\u00e9n plante\u00f3 la preocupaci\u00f3n de que should_flush_tlb() podr\u00eda no observar 'loaded_mm' e 'is_lazy' en el mismo orden en que switch_mm_irqs_off() los escribe. A\u00f1ade una barrera para garantizar que se observen en el orden en que est\u00e1n escritos."}], "lastModified": "2025-12-16T20:30:11.323", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "D2AFD248-20FC-485D-A1CC-13D0E8DCC81A", "versionEndExcluding": "5.15.183", "versionStartIncluding": "5.15.179"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "4C6814B6-DBF3-43D3-8C83-AB2A7B017FC6", "versionEndExcluding": "6.1.139", "versionStartIncluding": "6.1.129"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "7CC8774F-8BD4-4950-8F1C-0AD7E981084D", "versionEndExcluding": "6.6.91", "versionStartIncluding": "6.6.79"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "AC82108A-29E5-4E88-93EC-856824C6788E", "versionEndExcluding": "6.12.29", "versionStartIncluding": "6.12.16"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "8869956D-8A8C-40D1-91E5-1709F4A31C01", "versionEndExcluding": "6.14.7", "versionStartIncluding": "6.13.4"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:6.15:rc1:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "8D465631-2980-487A-8E65-40AE2B9F8ED1"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:6.15:rc2:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "4C9D071F-B28E-46EC-AC61-22B913390211"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:6.15:rc3:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "13FC0DDE-E513-465E-9E81-515702D49B74"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:6.15:rc4:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "8C7B5B0E-4EEB-48F5-B4CF-0935A7633845"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:6.15:rc5:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "2D240580-3048-49B2-9E27-F115A9DF8224"}], "operator": "OR"}]}, {"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "FA6FEEC2-9F11-4643-8827-749718254FED"}], "operator": "OR"}]}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}