CVE-2025-71089

In the Linux kernel, the following vulnerability has been resolved:

iommu: disable SVA when CONFIG_X86 is set

Patch series "Fix stale IOTLB entries for kernel address space", v7.

This proposes a fix for a security vulnerability related to IOMMU Shared

Virtual Addressing (SVA). In an SVA context, an IOMMU can cache kernel

page table entries. When a kernel page table page is freed and

reallocated for another purpose, the IOMMU might still hold stale,

incorrect entries. This can be exploited to cause a use-after-free or

write-after-free condition, potentially leading to privilege escalation or

data corruption.

This solution introduces a deferred freeing mechanism for kernel page

table pages, which provides a safe window to notify the IOMMU to

invalidate its caches before the page is reused.

This patch (of 8):

In the IOMMU Shared Virtual Addressing (SVA) context, the IOMMU hardware

shares and walks the CPU's page tables. The x86 architecture maps the

kernel's virtual address space into the upper portion of every process's

page table. Consequently, in an SVA context, the IOMMU hardware can walk

and cache kernel page table entries.

The Linux kernel currently lacks a notification mechanism for kernel page

table changes, specifically when page table pages are freed and reused.

The IOMMU driver is only notified of changes to user virtual address

mappings. This can cause the IOMMU's internal caches to retain stale

entries for kernel VA.

Use-After-Free (UAF) and Write-After-Free (WAF) conditions arise when

kernel page table pages are freed and later reallocated. The IOMMU could

misinterpret the new data as valid page table entries. The IOMMU might

then walk into attacker-controlled memory, leading to arbitrary physical

memory DMA access or privilege escalation. This is also a

Write-After-Free issue, as the IOMMU will potentially continue to write

Accessed and Dirty bits to the freed memory while attempting to walk the

stale page tables.

Currently, SVA contexts are unprivileged and cannot access kernel

mappings. However, the IOMMU will still walk kernel-only page tables all

the way down to the leaf entries, where it realizes the mapping is for the

kernel and errors out. This means the IOMMU still caches these

intermediate page table entries, making the described vulnerability a real

concern.

Disable SVA on x86 architecture until the IOMMU can receive notification

to flush the paging cache before freeing the CPU kernel page table pages.