CVE-2025-39961
Full vulnerability record from the local CVENow database.
Description
In the Linux kernel, the following vulnerability has been resolved: iommu/amd/pgtbl: Fix possible race while increase page table level The AMD IOMMU host page table implementation supports dynamic page table levels (up to 6 levels), starting with a 3-level configuration that expands based on IOVA address. The kernel maintains a root pointer and current page table level to enable proper page table walks in alloc_pte()/fetch_pte() operations. The IOMMU IOVA allocator initially starts with 32-bit address and onces its exhuasted it switches to 64-bit address (max address is determined based on IOMMU and device DMA capability). To support larger IOVA, AMD IOMMU driver increases page table level. But in unmap path (iommu_v1_unmap_pages()), fetch_pte() reads pgtable->[root/mode] without lock. So its possible that in exteme corner case, when increase_address_space() is updating pgtable->[root/mode], fetch_pte() reads wrong page table level (pgtable->mode). It does compare the value with level encoded in page table and returns NULL. This will result is iommu_unmap ops to fail and upper layer may retry/log WARN_ON. CPU 0 CPU 1 ------ ------ map pages unmap pages alloc_pte() -> increase_address_space() iommu_v1_unmap_pages() -> fetch_pte() pgtable->root = pte (new root value) READ pgtable->[mode/root] Reads new root, old mode Updates mode (pgtable->mode += 1) Since Page table level updates are infrequent and already synchronized with a spinlock, implement seqcount to enable lock-free read operations on the read path.
Severity
MEDIUM
CVSS score
4.7
(v3.1)
Vulnerability status
Modified
Source identifier
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Published
2025-10-09 13:15:32.250000
Last modified
2026-10-19 21:10:00.160000
View original CVE JSON
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"published": "2025-10-09T13:15:32.250",
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{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\niommu/amd/pgtbl: Fix possible race while increase page table level\n\nThe AMD IOMMU host page table implementation supports dynamic page table levels\n(up to 6 levels), starting with a 3-level configuration that expands based on\nIOVA address. The kernel maintains a root pointer and current page table level\nto enable proper page table walks in alloc_pte()/fetch_pte() operations.\n\nThe IOMMU IOVA allocator initially starts with 32-bit address and onces its\nexhuasted it switches to 64-bit address (max address is determined based\non IOMMU and device DMA capability). To support larger IOVA, AMD IOMMU\ndriver increases page table level.\n\nBut in unmap path (iommu_v1_unmap_pages()), fetch_pte() reads\npgtable->[root/mode] without lock. So its possible that in exteme corner case,\nwhen increase_address_space() is updating pgtable->[root/mode], fetch_pte()\nreads wrong page table level (pgtable->mode). It does compare the value with\nlevel encoded in page table and returns NULL. This will result is\niommu_unmap ops to fail and upper layer may retry/log WARN_ON.\n\nCPU 0 CPU 1\n------ ------\nmap pages unmap pages\nalloc_pte() -> increase_address_space() iommu_v1_unmap_pages() -> fetch_pte()\n pgtable->root = pte (new root value)\n READ pgtable->[mode/root]\n\t\t\t\t\t Reads new root, old mode\n Updates mode (pgtable->mode += 1)\n\nSince Page table level updates are infrequent and already synchronized with a\nspinlock, implement seqcount to enable lock-free read operations on the read path."
},
{
"lang": "es",
"value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\niommu/amd/pgtbl: Corrige una posible condición de carrera al aumentar el nivel de la tabla de páginas\n\nLa implementación de la tabla de páginas de host de AMD IOMMU soporta niveles de tabla de páginas dinámicos (hasta 6 niveles), comenzando con una configuración de 3 niveles que se expande basándose en la dirección IOVA. El kernel mantiene un puntero raíz y el nivel actual de la tabla de páginas para permitir recorridos adecuados de la tabla de páginas en las operaciones alloc_pte()/fetch_pte().\n\nEl asignador IOVA de IOMMU inicialmente comienza con una dirección de 32 bits y una vez que se agota, cambia a una dirección de 64 bits (la dirección máxima se determina basándose en la capacidad DMA del IOMMU y del dispositivo). Para soportar IOVA más grandes, el controlador AMD IOMMU aumenta el nivel de la tabla de páginas.\n\nPero en la ruta de desmapeo (iommu_v1_unmap_pages()), fetch_pte() lee pgtable->[root/mode] sin bloqueo. Así que es posible que en un caso extremo, cuando increase_address_space() está actualizando pgtable->[root/mode], fetch_pte() lea un nivel de tabla de páginas incorrecto (pgtable->mode). Compara el valor con el nivel codificado en la tabla de páginas y devuelve NULL. Esto resultará en que las operaciones iommu_unmap fallen y la capa superior puede reintentar/registrar WARN_ON.\n\nCPU 0 CPU 1\n------ ------\nmapear páginas desmapear páginas\nalloc_pte() -> increase_address_space() iommu_v1_unmap_pages() -> fetch_pte()\n pgtable->root = pte (nuevo valor raíz)\n LEER pgtable->[mode/root]\n\t\t\t\t\t Lee nueva raíz, modo antiguo\n Actualiza el modo (pgtable->mode += 1)\n\nDado que las actualizaciones del nivel de la tabla de páginas son poco frecuentes y ya están sincronizadas con un spinlock, se implementa seqcount para habilitar operaciones de lectura sin bloqueo en la ruta de lectura."
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