[PATCH v3] PCI: Fix crash during pci_dev hot-unplug on pseries KVM guest

[Michael Ellerman]

Bjorn Helgaas <helgaas at kernel.org> writes:
> On Sat, Aug 03, 2024 at 12:03:25AM +0530, Amit Machhiwal wrote:
>> With CONFIG_PCI_DYNAMIC_OF_NODES [1], a hot-plug and hot-unplug sequence
>> of a PCI device attached to a PCI-bridge causes following kernel Oops on
>> a pseries KVM guest:
>
> What is unique about pseries here?  There's nothing specific to
> pseries in the patch, so I would expect this to be a generic problem
> on any arch.
>
>>  RTAS: event: 2, Type: Hotplug Event (229), Severity: 1
>>  Kernel attempted to read user page (10ec00000048) - exploit attempt? (uid: 0)
>>  BUG: Unable to handle kernel data access on read at 0x10ec00000048
>
> Weird address.  I would expect NULL or something.  Where did this
> non-NULL pointer come from?

It originally comes from np->data, which is supposed to be an
of_changeset.

The powerpc code also uses np->data for the struct pci_dn pointer, see
pci_add_device_node_info().

I wonder if that's why it's non-NULL?

Amit, do we have exact steps to reproduce this? I poked around a bit but
couldn't get it to trigger.

cheers