CVE-2026-90387 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
swiotlb: Preserve allocation virtual address for dynamic pools
swiotlb_alloc_tlb() can allocate from the DMA atomic pool when a decrypted pool is needed from atomic context. With CONFIG_DMA_DIRECT_REMAP, the atomic pool is backed by remapped virtual addresses, which are not the same as the direct-map addresses returned by phys_to_virt().
swiotlb_init_io_tlb_pool() currently reconstructs the pool virtual address from the physical start address. For atomic-pool backed allocations this stores the wrong address in pool->vaddr. Later, swiotlb_free_tlb() passes that address to dma_free_from_pool(), which will fail to recognize the chunk
Pass the virtual address returned by the allocation path into swiotlb_init_io_tlb_pool(), and store that address in pool->vaddr. This keeps the pool free path using the same virtual address as the allocator.
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel's Software I/O Translation Lookaside Buffer, commonly known as SWIOTLB, serves as a critical subsystem for managing DMA operations on architectures where hardware translation tables are either unavailable or insufficiently configured to handle all memory addresses directly. A recent resolution addresses a subtle but significant logical error within the dynamic pool management mechanisms of this subsystem, specifically concerning how virtual addresses are tracked and freed when dealing with decrypted pools in atomic contexts. This issue arises primarily under configurations that enable CONFIG_DMA_DIRECT_REMAP, which alters the mapping strategy for DMA buffers to ensure proper cache coherency and security isolation by using remapped virtual addresses rather than simple direct mappings derived from physical addresses.
The core technical flaw lies in the initialization logic of the IO TLB pool when it is backed by the atomic memory pool. When swiotlb_alloc_tlb() requests a buffer for decryption purposes within an atomic context, the underlying allocator provides a remapped virtual address that differs from the direct-map address one would expect if calculated via phys_to_virt(). However, the function swiotlb_init_io_tlb_pool() was previously reconstructing the pool's virtual address by converting its physical start address back to a virtual address using this direct-mapping method. This resulted in storing an incorrect virtual address in the pool structure member vaddr, creating a mismatch between the actual memory location allocated and the metadata recorded for future deallocation operations.
This discrepancy manifests during the cleanup phase when swiotlb_free_tlb() attempts to release the buffer back into the system. The function passes the stored, but now incorrect, virtual address to dma_free_from_pool(). Because this address does not match the actual remapped allocation returned by the allocator earlier, the memory management subsystem fails to recognize the chunk as a valid allocation belonging to that specific pool. Consequently, the free operation is likely to fail or behave unpredictably, potentially leading to resource leaks where allocated DMA buffers are never properly released back to the system's available memory pools. In severe cases, such mismatches can trigger kernel panics due to invalid pointer dereferences or corruption of internal allocator data structures that rely on accurate address tracking for integrity checks.
From a vulnerability classification perspective, this issue aligns with CWE-401, which describes a missing release of memory after effective allocation, and more broadly with CWE-755, relating to improper handling of unusual input situations where the system fails to correctly process data due to logical errors in address translation. The operational impact is primarily centered on resource exhaustion and stability degradation rather than direct remote code execution or privilege escalation. However, because DMA operations are fundamental to device communication, persistent failures in freeing these buffers can lead to progressive memory pressure that may eventually cause denial of service conditions for the entire system or specific devices relying on SWIOTLB for data transfer.
The remediation involves a straightforward but critical correction to the initialization flow: passing the actual virtual address returned by the allocation path directly into swiotlb_init_io_tlb_pool() and storing this correct value in pool->vaddr. This ensures that the free path utilizes the exact same virtual address as the allocator, maintaining consistency across the lifecycle of the DMA buffer. By aligning the deallocation logic with the actual memory mapping strategy employed by CONFIG_DMA_DIRECT_REMAP, the kernel prevents the mismatch that causes free failures. System administrators and developers should ensure their kernels are updated to include this patch, particularly on architectures where SWIOTLB is heavily utilized for I/O operations involving decrypted buffers in atomic contexts, such as certain ARM64 or RISC-V implementations with specific DMA coherence requirements.