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

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 26 Mar 2020 13:29:01 +0100
Igor Mammedov <imammedo@redhat.com> wrote:

> On Thu, 26 Mar 2020 11:52:36 +0000
> Peter Maydell <peter.maydell@linaro.org> 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?  
> 
> 0 is not valid value, we should ignore and return early in this case
> like we do with bsel. I'll post a path shortly.
well, looking more that is only true for main bus, for bridges it can be
slot number can be zero, then AML left shifts it and writes into B0EJ
which traps into pci_write(, data) and that is supposed to eject
slot 0 according to guest(AML).

Michael,
what's your take on it?

> 
> > 
> > thanks
> > -- PMM
> >   
> 
>