Linux Kernel IB/hfi1 PIO_CRED mmap Pointer Arithmetic Is Off by a Factor of 64, Mapping the Wrong Physical Memory Region

Status: UPDATED  |  Advisory ID: CVE-2026-98216

Key Details

Affected Products, Subsystems & Sectors

What to Know

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

IB/hfi1: Fix the PIO_CRED credit-return mmap

hfi1_file_mmap()'s PIO_CRED case must hand user space the single

credit-return page that holds this context's entry. That page is the

second or third page of the per-node credit-return allocation once the

hardware send context index reaches 64 or 128, so the failure below is

intermittent: when the entry lands on the first page the offset is zero

and everything works.

Two things are wrong.

First, cr_page_offset is a byte offset but .va is a struct

credit_return *, so adding it is pointer arithmetic and scales the offset

by sizeof(struct credit_return) == 64. memvirt then lands 256 KiB or

512 KiB past a 10240-byte allocation. With an IOMMU translating, that

address is inside the vmalloc range but in no vm_area, so

dma_mmap_coherent() -> iommu_dma_mmap() finds no pages, vmalloc_to_pfn()

returns page_to_pfn(NULL), and remap_pfn_range() installs a frame above

MAXPHYADDR. The first user read then takes:

psm2_ep_open_pr: Corrupted page table at address 7a14d007e000

PGD 800000013886a067 P4D 800000013886a067 PUD 13886b067 PMD 13886c067

PTE 800049168e911235

Oops: Bad pagetable: 000d [#1] SMP PTI

Second, and still wrong once the arithmetic is corrected,

dma_mmap_coherent() describes a whole coherent buffer and selects the

page within it with vma->vm_pgoff. Offsetting cpu_addr has no effect:

for a vmap'd allocation iommu_dma_mmap() uses cpu_addr only to locate the

vm_area and then maps pages[vm_pgoff], which hfi1_file_mmap() has just

set to 0. User space therefore always receives the first credit-return

page, every credit read is for the wrong context, and send PIO stalls

forever.

Use the DMA API as intended: pass the base of the allocation with its

full length and select the page with vm_pgoff. A separate length is

needed because memlen must keep describing the VMA for the existing size

check. The dma-direct path stays correct as well, since dma_direct_mmap()

adds the same vm_pgoff to the base pfn.

Tested on a Dell T7610 (Xeon E5-2650 v2, Intel IOMMU in DMA-FQ mode)

against a Threadripper PRO 3995WX peer, both Omni-Path 100. Before this

change psm2_ep_open() Oopses the kernel; with only the arithmetic

corrected psm2_ep_open() succeeds but any transfer that uses send PIO

hangs, PSM2_SDMA=2 (send PIO disabled) completing normally while

PSM2_SDMA=0 (send PIO only) hangs every time. With this change send PIO,

send DMA and the default mixed mode all work. (NVD)

What to Do

Monitor Linux's web page for any future patch releases.

References