This bug is found in Zhaoxin platform, but it's a commom code bug. Fail sequence: step1: Unbind UHCI controller from native driver; step2: Bind UHCI controller to vfio-pci, which will put UHCI controller in one vfio        group's device list and set UHCI's dev->driver_data to struct vfio-pci(for UHCI) step3: Unbind EHCI controller from native driver, will try to tell UHCI native driver        that "I'm removed by set companion_hcd->self.hs_companion to NULL. However,        companion_hcd get from UHCI's dev->driver_data that has modified by vfio-pci        already.So, the vfio-pci structure will be damaged! step4: Bind EHCI controller to vfio-pci driver, which will put EHCI controller in the        same vfio group as UHCI controller;      ... ... step5: Unbind UHCI controller from vfio-pci, which will delete UHCI from vfio group'        device list that has been damaged in step 3. So,delete operation can random        result into a NULL pointer dereference with the below stack dump. step6: Bind UHCI controller to native driver; step7: Unbind EHCI controller from vfio-pci, which will try to remove EHCI controller        from the vfio group; step8: Bind EHCI controller to native driver; [  929.114641] uhci_hcd 0000:00:10.0: remove, state 1 [ 929.114652] usb usb1: USB disconnect, device number 1 [ 929.114655] usb 1-1: USB disconnect, device number 2 [ 929.270313] usb 1-2: USB disconnect, device number 3 [ 929.318404] uhci_hcd 0000:00:10.0: USB bus 1 deregistered [ 929.343029] uhci_hcd 0000:00:10.1: remove, state 4 [  929.343045] usb usb3: USB disconnect, device number 1 [  929.343685] uhci_hcd 0000:00:10.1: USB bus 3 deregistered [  929.369087] ehci-pci 0000:00:10.7: remove, state 4 [  929.369102] usb usb4: USB disconnect, device number 1 [  929.370325] ehci-pci 0000:00:10.7: USB bus 4 deregistered [  932.398494] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000 [  932.398496] PGD 42a67d067 P4D 42a67d067 PUD 42a65f067 PMD 0 [  932.398502] Oops: 0002 [#2] SMP NOPTI [  932.398505] CPU: 2 PID: 7824 Comm: vfio_unbind.sh Tainted: P D  4.19.65-2020051917-rainos #1 [  932.398506] Hardware name: Shanghai Zhaoxin Semiconductor Co., Ltd. HX002EH/HX002EH,            BIOS HX002EH0_01_R480_R_200408 04/08/2020 [ 932.398513] RIP: 0010:vfio_device_put+0x31/0xa0 [vfio] [ 932.398515] Code: 89 e5 41 54 53 4c 8b 67 18 48 89 fb 49 8d 74 24 30 e8 e3 0e f3 de         84 c0 74 67 48 8b 53 20 48 8b 43 28 48 8b 7b 18 48 89 42 08 <48> 89 10         48 b8 00 01 00 00 00 00 ad de 48 89 43 20 48 b8 00 02 00 [  932.398516] RSP: 0018:ffffbbfd04cffc18 EFLAGS: 00010202 [ 932.398518] RAX: 0000000000000000 RBX: ffff92c7ea717880 RCX: 0000000000000000 [  932.398519] RDX: ffff92c7ea713620 RSI: ffff92c7ea713630 RDI: ffff92c7ea713600 [  932.398521] RBP: ffffbbfd04cffc28 R08: ffff92c7f02a8080 R09: ffff92c7efc03980 [ 932.398522] R10: ffffbbfd04cff9a8 R11: 0000000000000000 R12: ffff92c7ea713600 [  932.398523] R13: ffff92c7ed8bb0a8 R14: ffff92c7ea717880 R15: 0000000000000000 [  932.398525] FS: 00007f3031500740(0000) GS:ffff92c7f0280000(0000) knlGS:0000000000000000 [  932.398526] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [  932.398527] CR2: 0000000000000000 CR3: 0000000428626004 CR4: 0000000000160ee0 [  932.398528] Call Trace: [  932.398534]  vfio_del_group_dev+0xe8/0x2a0 [vfio] [ 932.398539]  ? __blocking_notifier_call_chain+0x52/0x60 [  932.398542]  ? do_wait_intr_irq+0x90/0x90 [  932.398546]  ? iommu_bus_notifier+0x75/0x100 [  932.398551] vfio_pci_remove+0x20/0xa0 [vfio_pci] [  932.398554] pci_device_remove+0x3e/0xc0 [  932.398557] device_release_driver_internal+0x17a/0x240 [  932.398560]  device_release_driver+0x12/0x20 [  932.398561] unbind_store+0xee/0x180 [  932.398564]  drv_attr_store+0x27/0x40 [  932.398567]  sysfs_kf_write+0x3c/0x50 [  932.398568] kernfs_fop_write+0x125/0x1a0 [  932.398572] __vfs_write+0x3a/0x190 [  932.398575]  ? apparmor_file_permission+0x1a/0x20 [  932.398577]  ? security_file_permission+0x3b/0xc0 [  932.398581]  ? _cond_resched+0x1a/0x50 [  932.398582] vfs_write+0xb8/0x1b0 [  932.398584]  ksys_write+0x5c/0xe0 [ 932.398586]  __x64_sys_write+0x1a/0x20 [  932.398589] do_syscall_64+0x5a/0x110 [  932.398592] entry_SYSCALL_64_after_hwframe+0x44/0xa9 Using virt-manager/qemu to boot guest os, we can see the same fail sequence! Fix this by determine whether the PCI Driver of the USB controller is a kernel native driver. If not, do not let it modify UHCI's dev->driver_data. Signed-off-by: LeoLiu-oc <LeoLiu-oc@zhaoxin.com> ---  drivers/usb/core/hcd-pci.c | 10 ++++++++++  1 file changed, 10 insertions(+) diff --git a/drivers/usb/core/hcd-pci.c b/drivers/usb/core/hcd-pci.c index 7537681355f6..c3cddaab708d 100644 --- a/drivers/usb/core/hcd-pci.c +++ b/drivers/usb/core/hcd-pci.c @@ -49,6 +49,7 @@ static void for_each_companion(struct pci_dev *pdev, struct usb_hcd *hcd,      struct pci_dev        *companion;      struct usb_hcd        *companion_hcd;      unsigned int        slot = PCI_SLOT(pdev->devfn); +    struct pci_driver    *drv;      /*       * Iterate through other PCI functions in the same slot. @@ -61,6 +62,15 @@ static void for_each_companion(struct pci_dev *pdev, struct usb_hcd *hcd,                  PCI_SLOT(companion->devfn) != slot)              continue; +        drv = companion->driver; +        if (!drv) +            continue; + +        if (strncmp(drv->name, "uhci_hcd", sizeof("uhci_hcd") - 1) && +            strncmp(drv->name, "ooci_hcd", sizeof("uhci_hcd") - 1) && +            strncmp(drv->name, "ehci_hcd", sizeof("uhci_hcd") - 1)) +            continue; +          /*           * Companion device should be either UHCI,OHCI or EHCI host           * controller, otherwise skip. -- 2.20.1