CVE-2025-39961
Vulnérabilité élevée dans Linux (Linux)
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.
Gravité et risque d'exploitation
CVE-2025-39961 obtient un score CVSS de 8.8/10, soit une gravité élevée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.11 %, ce qui la place devant 1.4 % des CVE référencées.
Que faire ?
- Vérifiez si Linux (versions <=6.12.*, <=6.16.*, 4.9.194, 6.12.49, 6.17, 0, 6.16.9, 4.19.75, <4.10, 6fb92f18555a7b8e085267d513612dc0ff9a5360, 0d50f7b1e8c80a8c20db5049e269468c059b0378, <075abf0b1a958acfbea2435003d228e738e90346, <4.20, <=6.6.*, <1e56310b40fd2e7e0b9493da9ff488af145bdd0c, 5.3, 4.14.146, <5.3, 6.6.108, 754265bcab78a9014f0f99cd35e0d610fcd7dfa7, 785ca708a908b9c596ede852470ba28b8dc3e40b, <=*, 5.2.17, b15bf74405faa1a65025eb8a6eb337e140e5250a, <7d462bdecb7d9c32934dab44aaeb7ea7d73a27a2, <cd92c8ab336c3a633d46e6f35ebcd3509ae7db3b, <4.15) est présent sur votre parc.
- Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
- À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
- Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.