4.4 KiB
CVE-2025-22022
Description
In the Linux kernel, the following vulnerability has been resolved:usb: xhci: Apply the link chain quirk on NEC isoc endpointsTwo clearly different specimens of NEC uPD720200 (one with start/stopbug, one without) were seen to cause IOMMU faults after some MissedService Errors. Faulting address is immediately after a transfer ringsegment and patched dynamic debug messages revealed that the MSE wasreceived when waiting for a TD near the end of that segment:[ 1.041954] xhci_hcd: Miss service interval error for slot 1 ep 2 expected TD DMA ffa08fe0[ 1.042120] xhci_hcd: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x0005 address=0xffa09000 flags=0x0000][ 1.042146] xhci_hcd: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x0005 address=0xffa09040 flags=0x0000]It gets even funnier if the next page is a ring segment accessible tothe HC. Below, it reports MSE in segment at ff1e8000, plows through azero-filled page at ff1e9000 and starts reporting events for TRBs inpage at ff1ea000 every microframe, instead of jumping to seg ff1e6000.[ 7.041671] xhci_hcd: Miss service interval error for slot 1 ep 2 expected TD DMA ff1e8fe0[ 7.041999] xhci_hcd: Miss service interval error for slot 1 ep 2 expected TD DMA ff1e8fe0[ 7.042011] xhci_hcd: WARN: buffer overrun event for slot 1 ep 2 on endpoint[ 7.042028] xhci_hcd: All TDs skipped for slot 1 ep 2. Clear skip flag.[ 7.042134] xhci_hcd: WARN: buffer overrun event for slot 1 ep 2 on endpoint[ 7.042138] xhci_hcd: ERROR Transfer event TRB DMA ptr not part of current TD ep_index 2 comp_code 31[ 7.042144] xhci_hcd: Looking for event-dma 00000000ff1ea040 trb-start 00000000ff1e6820 trb-end 00000000ff1e6820[ 7.042259] xhci_hcd: WARN: buffer overrun event for slot 1 ep 2 on endpoint[ 7.042262] xhci_hcd: ERROR Transfer event TRB DMA ptr not part of current TD ep_index 2 comp_code 31[ 7.042266] xhci_hcd: Looking for event-dma 00000000ff1ea050 trb-start 00000000ff1e6820 trb-end 00000000ff1e6820At some point completion events change from Isoch Buffer Overrun toShort Packet and the HC finally finds cycle bit mismatch in ff1ec000.[ 7.098130] xhci_hcd: ERROR Transfer event TRB DMA ptr not part of current TD ep_index 2 comp_code 13[ 7.098132] xhci_hcd: Looking for event-dma 00000000ff1ecc50 trb-start 00000000ff1e6820 trb-end 00000000ff1e6820[ 7.098254] xhci_hcd: ERROR Transfer event TRB DMA ptr not part of current TD ep_index 2 comp_code 13[ 7.098256] xhci_hcd: Looking for event-dma 00000000ff1ecc60 trb-start 00000000ff1e6820 trb-end 00000000ff1e6820[ 7.098379] xhci_hcd: Overrun event on slot 1 ep 2It's possible that data from the isochronous device were written torandom buffers of pending TDs on other endpoints (either IN or OUT),other devices or even other HCs in the same IOMMU domain.Lastly, an error from a different USB device on another HC. Was itcaused by the above? I don't know, but it may have been. The diskwas working without any other issues and generated PCIe traffic tostarve the NEC of upstream BW and trigger those MSEs. The two HCsshared one x1 slot by means of a commercial "PCIe splitter" board.[ 7.162604] usb 10-2: reset SuperSpeed USB device number 3 using xhci_hcd[ 7.178990] sd 9:0:0:0: [sdb] tag#0 UNKNOWN(0x2003) Result: hostbyte=0x07 driverbyte=DRIVER_OK cmd_age=0s[ 7.179001] sd 9:0:0:0: [sdb] tag#0 CDB: opcode=0x28 28 00 04 02 ae 00 00 02 00 00[ 7.179004] I/O error, dev sdb, sector 67284480 op 0x0:(READ) flags 0x80700 phys_seg 5 prio class 0Fortunately, it appears that this ridiculous bug is avoided by settingthe chain bit of Link TRBs on isochronous rings. Other ancient HCs areknown which also expect the bit to be set and they ignore Link TRBs ifit's not. Reportedly, 0.95 spec guaranteed that the bit is set.The bandwidth-starved NEC HC running a 32KB/uframe UVC endpoint reportstens of MSEs per second and runs into the bug within seconds. ChainingLink TRBs allows the same workload to run for many minutes, many times.No ne---truncated---
POC
Reference
No PoCs from references.