CVE-2026-98254 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
swiotlb: use the adjusted address for the highmem page lookup
swiotlb_bounce() reads the page frame number from the slot's recorded orig_addr, then advances orig_addr by tlb_offset to reach the address the caller asked about. The highmem branch mixes the two: the offset within the page comes from the adjusted address, the page from the value before it.
Once the adjustment crosses a page boundary the pair no longer describes one location, and the whole copy lands one page below the intended one for a positive tlb_offset, one above for a negative one. DMA_FROM_DEVICE writes the device data over the wrong page and leaves the intended one stale, DMA_TO_DEVICE feeds the device from a page the mapping may not cover. Partial syncs through dma_sync_single_range_for_*() are what make tlb_offset non-zero.
The branch test is picked the same way, so a slot recorded in lowmem can be adjusted into highmem and the lowmem path then hands a highmem address to phys_to_virt().
Take both from orig_addr once it is final and keep pfn in the branch that uses it. PhysHighMem() asks the question straight from the address, as dma-debug already does.
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Analysis
by VulDB Data Team • 10/06/2026
The Linux kernel contains a critical logic error within the Software Translation Lookaside Buffer (SWIOTLB) bounce buffer implementation specifically affecting high memory page lookups during DMA operations. SWIOTLB is responsible for managing situations where devices cannot directly access all physical memory, requiring data to be copied between device-accessible buffers and system memory. The vulnerability resides in the swiotlb_bounce function which handles these transfers by reading a page frame number from an original address recorded in a slot structure. This process involves adjusting addresses based on offsets derived from partial synchronization requests via dma_sync_single_range_for_* functions, where tlb_offset becomes non-zero to handle specific ranges within mapped buffers rather than entire mappings.
The core technical flaw is a mismatch between the source of page identification and offset calculation when dealing with high memory pages. The code incorrectly mixes two different address values during this process: it uses an adjusted address for calculating the byte offset within a page but retrieves the actual physical page frame number from the unadjusted original address. This separation creates a dangerous inconsistency because once any adjustment crosses a page boundary, these two values no longer correspond to the same memory location. For positive offsets resulting in forward movement across pages, the copy operation targets one page below what was intended; conversely negative offsets cause writes or reads targeting one page above the correct destination.
This addressing error leads directly to severe operational impacts depending on the direction of data transfer. In DMA_FROM_DEVICE scenarios where hardware writes received data into system memory, the kernel copies incoming device data over an incorrect physical page while leaving the actual intended buffer stale and containing outdated information. This results in application-level corruption as programs receive garbled or incomplete data from their peripherals such as network interfaces or storage controllers. Conversely for DMA_TO_DEVICE operations where system data is sent to hardware devices, the kernel feeds transmission buffers that may not even be covered by valid memory mappings potentially causing page faults device errors or silent data loss depending on how strictly the underlying architecture enforces access controls and boundary checks during direct memory access transactions.
The vulnerability also introduces a secondary risk related to memory zone classification logic within low versus high memory boundaries. The branch selection mechanism relies on similar address manipulation patterns that can cause slots originally recorded in standard lowmem regions to be adjusted into highmem space through offset calculations yet subsequently processed by paths designed for lower memory zones. This mismatch allows the system to pass addresses belonging to high memory pages directly to phys_to_virt conversion routines expecting low memory pointers which violates kernel assumptions about virtual mapping availability and can trigger undefined behavior or crashes when attempting to dereference unmapped virtual address spaces associated with physically contiguous but virtually disjointed regions of RAM typically reserved for special purposes like persistent allocations or non-cacheable device mappings.
Mitigation strategies should prioritize applying the upstream Linux kernel patch that corrects this logical inconsistency by ensuring both page frame retrieval and offset calculations derive consistently from the final adjusted original address once all modifications are complete rather than mixing pre-adjustment identifiers with post-adjustment offsets thereby maintaining referential integrity throughout bounce buffer operations developers must also verify their systems run patched versions of affected kernels particularly those utilizing SWIOTLB extensively for devices requiring coherent DMA transfers across large contiguous blocks exceeding direct mapping capabilities organizations managing fleets should monitor vendor security advisories and deploy updates promptly since exploitation could lead to arbitrary code execution through crafted peripheral interactions or denial-of-service via memory corruption affecting critical subsystems handling real-time data streams from external hardware components without proper patching the risk remains persistent until corrected at source level within mainline distributions.