Bug 2420416 (CVE-2025-40336)

Summary: CVE-2025-40336 kernel: drm/gpusvm: fix hmm_pfn_to_map_order() usage
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in the Linux kernel's GPU shared virtual memory (gpusvm) subsystem. When handling HMM (Heterogeneous Memory Management) ranges that partially cover a huge page (such as 2MB pages), the hmm_pfn_to_map_order() function may incorrectly map memory outside the intended range. This could result in mapping memory that is not mapped by the process's memory management, potentially exposing unauthorized memory regions or causing memory corruption.
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Description OSIDB Bzimport 2025-12-09 05:01:56 UTC 
In the Linux kernel, the following vulnerability has been resolved:

drm/gpusvm: fix hmm_pfn_to_map_order() usage

Handle the case where the hmm range partially covers a huge page (like
2M), otherwise we can potentially end up doing something nasty like
mapping memory which is outside the range, and maybe not even mapped by
the mm. Fix is based on the xe userptr code, which in a future patch
will directly use gpusvm, so needs alignment here.

v2:
  - Add kernel-doc (Matt B)
  - s/fls/ilog2/ (Thomas)
Comment 1 Alexander B 2025-12-09 13:34:01 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025120911-CVE-2025-40336-781e@gregkh/T