CVE-2026-80861: usb: xhci: bail out of setup if the controller is inaccessible

CVE-2026-80861: usb: xhci: bail out of setup if the controller is inaccessible

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

usb: xhci: bail out of setup if the controller is inaccessible

xhci_gen_setup() locates the operational registers using the capability
length read from the very first register:

	xhci->op_regs = hcd->regs +
		HC_LENGTH(readl(&xhci->cap_regs->hc_capbase));

If the controller is dead or has dropped off the bus, that read returns
~0, HC_LENGTH() truncates it to 0xff, and op_regs ends up 0xff bytes
past the page-aligned MMIO base, i.e. unaligned. The first access
through it, xhci_halt() -> xhci_handshake() reading op_regs->status, is
then an unaligned readl() on device memory. arm64 faults on unaligned
device accesses, so instead of xhci_handshake() catching the all-ones
value and returning -ENODEV, setup oopses:

  xhci-pci-renesas 0005:08:00.0: Unable to change power state from D3cold to D0, device inaccessible
  xhci-pci-renesas 0005:08:00.0: xHCI Host Controller
  xhci-pci-renesas 0005:08:00.0: new USB bus registered, assigned bus number 1
  Unable to handle kernel paging request at virtual address ffff80030a770103
    ESR = 0x0000000096000021
    FSC = 0x21: alignment fault
  Internal error: Oops: 0000000096000021 [#1]  SMP
  pc : xhci_halt [xhci_hcd]
  Call trace:
   xhci_halt
   xhci_gen_setup
   xhci_pci_setup
   usb_add_hcd
   usb_hcd_pci_probe
   xhci_pci_common_probe
   xhci_pci_renesas_probe

This was hit with a Renesas uPD720201 that failed to power up ("Unable
to change power state from D3cold to D0, device inaccessible") yet still
reached the HCD probe path.

Read the capability register once, and if it reads back the all-ones
value (as xhci_handshake() and xhci_reset() already test for), abort
setup with -ENODEV before op_regs is derived from it. Reading it once
also avoids re-reading a register that may change under a concurrent
hot-removal.

The Linux kernel CVE team has assigned CVE-2026-80861 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 2.6.31 with commit 66d4eadd8d067269ea8fead1a50fe87c2979a80d and fixed in 7.1.13 with commit bf84c6b0264947794fa783c324a6d874ca6657d8
	Issue introduced in 2.6.31 with commit 66d4eadd8d067269ea8fead1a50fe87c2979a80d and fixed in 7.2.3 with commit 0b31744f70c5e06cce5fb660e02d057a3b9e0e37
	Issue introduced in 2.6.31 with commit 66d4eadd8d067269ea8fead1a50fe87c2979a80d and fixed in 7.3-rc1 with commit 78203d5b54a40f0e36196ebf31c9c7a380fc8811

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-80861
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/usb/host/xhci.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/bf84c6b0264947794fa783c324a6d874ca6657d8
	https://git.kernel.org/stable/c/0b31744f70c5e06cce5fb660e02d057a3b9e0e37
	https://git.kernel.org/stable/c/78203d5b54a40f0e36196ebf31c9c7a380fc8811