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Re: acpi_pcihp_eject_slot() bug if passed 'slots == 0'

From: Igor Mammedov
Subject: Re: acpi_pcihp_eject_slot() bug if passed 'slots == 0'
Date: Thu, 26 Mar 2020 14:23:17 +0100

On Thu, 26 Mar 2020 11:52:36 +0000
Peter Maydell <address@hidden> wrote:

> Hi; Coverity spots that if hw/acpi/pcihp.c:acpi_pcihp_eject_slot()
> is passed a zero 'slots' argument then ctz32(slots) will return 32,
> and then the code that does '1U << slot' is C undefined behaviour
> because it's an oversized shift. (This is CID 1421896.)
> Since the pci_write() function in this file can call
> acpi_pcihp_eject_slot() with an arbitrary value from the guest,
> I think we need to handle 'slots == 0' safely. But what should
> the behaviour be?

it also uncovers a bug, where we are not able to eject slot 0 on bridge,
can be reproduced with:

 -enable-kvm -m 4G -device pci-bridge,chassis_nr=1 -global 
PIIX4_PM.acpi-pci-hotplug-with-bridge-support=on -device 

(monitor) device_del netdev12
(monitor) qtree # still shows the device

reason is that acpi_pcihp_eject_slot()
   if (PCI_SLOT(dev->devfn) == slot) { # doesn't  match (0 != 32)

so device is not deleted

> thanks
> -- PMM

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