UBUNTU-CVE-2025-22022: Buffer Overflow
In the Linux kernel, the following vulnerability has been resolved: usb: xhci: Apply the link chain quirk on NEC isoc endpoints Two clearly different specimens of NEC uPD720200 (one with start/stop bug, one without) were seen to cause IOMMU faults after some Missed Service Errors. Faulting address is immediately after a transfer ring segment and patched dynamic debug messages revealed that the MSE was received when waiting for a TD near the end of that segment: [ 1.041954] xhcihcd: Miss service interval error for slot 1 ep 2 expected TD DMA ffa08fe0 [ 1.042120] xhcihcd: AMD-Vi: Event logged [IOPAGEFAULT domain=0x0005 address=0xffa09000 flags=0x0000] [ 1.042146] xhcihcd: AMD-Vi: Event logged [IOPAGEFAULT domain=0x0005 address=0xffa09040 flags=0x0000] It gets even funnier if the next page is a ring segment accessible to the HC. Below, it reports MSE in segment at ff1e8000, plows through a zero-filled page at ff1e9000 and starts reporting events for TRBs in page at ff1ea000 every microframe, instead of jumping to seg ff1e6000. [ 7.041671] xhcihcd: Miss service interval error for slot 1 ep 2 expected TD DMA ff1e8fe0 [ 7.041999] xhcihcd: Miss service interval error for slot 1 ep 2 expected TD DMA ff1e8fe0 [ 7.042011] xhcihcd: WARN: buffer overrun event for slot 1 ep 2 on endpoint [ 7.042028] xhcihcd: All TDs skipped for slot 1 ep 2. Clear skip flag. [ 7.042134] xhcihcd: WARN: buffer overrun event for slot 1 ep 2 on endpoint [ 7.042138] xhcihcd: ERROR Transfer event TRB DMA ptr not part of current TD epindex 2 compcode 31 [ 7.042144] xhcihcd: Looking for event-dma 00000000ff1ea040 trb-start 00000000ff1e6820 trb-end 00000000ff1e6820 [ 7.042259] xhcihcd: WARN: buffer overrun event for slot 1 ep 2 on endpoint [ 7.042262] xhcihcd: ERROR Transfer event TRB DMA ptr not part of current TD epindex 2 compcode 31 [ 7.042266] xhcihcd: Looking for event-dma 00000000ff1ea050 trb-start 00000000ff1e6820 trb-end 00000000ff1e6820 At some point completion events change from Isoch Buffer Overrun to Short Packet and the HC finally finds cycle bit mismatch in ff1ec000. [ 7.098130] xhcihcd: ERROR Transfer event TRB DMA ptr not part of current TD epindex 2 compcode 13 [ 7.098132] xhcihcd: Looking for event-dma 00000000ff1ecc50 trb-start 00000000ff1e6820 trb-end 00000000ff1e6820 [ 7.098254] xhcihcd: ERROR Transfer event TRB DMA ptr not part of current TD epindex 2 compcode 13 [ 7.098256] xhcihcd: Looking for event-dma 00000000ff1ecc60 trb-start 00000000ff1e6820 trb-end 00000000ff1e6820 [ 7.098379] xhcihcd: Overrun event on slot 1 ep 2 It's possible that data from the isochronous device were written to random 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 it caused by the above? I don't know, but it may have been. The disk was working without any other issues and generated PCIe traffic to starve the NEC of upstream BW and trigger those MSEs. The two HCs shared one x1 slot by means of a commercial "PCIe splitter" board. [ 7.162604] usb 10-2: reset SuperSpeed USB device number 3 using xhcihcd [ 7.178990] sd 9:0:0:0: [sdb] tag#0 UNKNOWN(0x2003) Result: hostbyte=0x07 driverbyte=DRIVEROK cmdage=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 physseg 5 prio class 0 Fortunately, it appears that this ridiculous bug is avoided by setting the chain bit of Link TRBs on isochronous rings. Other ancient HCs are known which also expect the bit to be set and they ignore Link TRBs if it's not. Reportedly, 0.95 spec guaranteed that the bit is set. The bandwidth-starved NEC HC running a 32KB/uframe UVC endpoint reports tens of MSEs per second and runs into the bug within seconds. Chaining Link TRBs allows the same workload to run for many minutes, many times. No ne ---truncated---
Affected Software
Remediation
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Set the chain bit on Link TRBs used by isochronous transfer rings; apply the Link TRB chain quirk for NEC isochronous endpoints.
Linux xHCI driver on NEC uPD720200 isochronous endpoints Chain bit on Link TRBs = set
Event History
Frequently Asked Questions
Which systems are most likely to be exposed?
Systems using an NEC uPD720200 USB controller with isochronous endpoints are implicated. The listed affected Ubuntu kernel packages include the standard, AWS, Azure, GCP, and FIPS kernel variants.
What level of access does an attacker need?
The severity vector indicates local attack vector, low attack complexity, low privileges required, and no user interaction. The reported impact is high availability impact and low integrity impact, with no confidentiality impact.
How can I look for signs that this issue is occurring?
The described symptom is IOMMU fault logging after xHCI Missed Service Errors, including messages such as "Miss service interval error" and AMD-Vi "IO_PAGE_FAULT" events. The faults may reference addresses immediately after a transfer-ring segment.