On Tue, 24 Aug 2021, Igor Mammedov wrote:
> On Mon, 23 Aug 2021 19:06:47 -0400
> "Michael S. Tsirkin" <m...@redhat.com> wrote:
>
> > On Sat, Aug 21, 2021 at 08:35:35PM +0530, Ani Sinha wrote:
> > > Bsel property of the pci bus indicates whether the bus supports acpi
> > > hotplug.
> > > We need to validate the presence of this property before performing any
> > > hotplug
> > > related callback operations. Currently validation of the existence of this
> > > property was absent from acpi_pcihp_device_unplug_cb() function but is
> > > present
> > > in other hotplug/unplug callback functions. Hence, this change adds the
> > > missing
> > > check for the above function.
> > >
> > > Signed-off-by: Ani Sinha <a...@anisinha.ca>
> >
> > I queued this but I have a general question:
> I convinced myself that this patch is wrong, pls drop it.
>
> > are all these errors logged with LOG_GUEST_ERROR?
> > Because if not we have a security problem.
> > I also note that bsel is an internal property,
> > I am not sure we should be printing this to users,
> > it might just confuse them.
> >
> > Same question for all the other places validating bsel.
>
> Commit message misses reproducer/explanation about
> how it could be triggered?
>
> If it's actually reachable, from my point of view
> putting checks all through out call chain is not robust
> and it's easy to miss issues caused by invalid bsel.
> Instead of putting check all over the code, I'd
> check value on entry points (pci_read/pci_write)
> if code there is broken.
>
> >
> > > ---
> > > hw/acpi/pcihp.c | 10 ++++++++--
> > > 1 file changed, 8 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c
> > > index 0fd0c1d811..9982815a87 100644
> > > --- a/hw/acpi/pcihp.c
> > > +++ b/hw/acpi/pcihp.c
> > > @@ -372,9 +372,15 @@ void acpi_pcihp_device_unplug_cb(HotplugHandler
> > > *hotplug_dev, AcpiPciHpState *s,
> > > DeviceState *dev, Error **errp)
> > > {
> > > PCIDevice *pdev = PCI_DEVICE(dev);
> > > + int bsel = acpi_pcihp_get_bsel(pci_get_bus(pdev));
> > > +
> > > + trace_acpi_pci_unplug(PCI_SLOT(pdev->devfn), bsel);
> > >
> > > - trace_acpi_pci_unplug(PCI_SLOT(pdev->devfn),
> > > - acpi_pcihp_get_bsel(pci_get_bus(pdev)));
> > > + if (bsel < 0) {
> > > + error_setg(errp, "Unsupported bus. Bus doesn't have property '"
> > > + ACPI_PCIHP_PROP_BSEL "' set");
> > > + return;
> > > + }
>
> 1st:
> Error here is useless. this path is triggered on guest
> MMIO write and there is no consumer for error whatsoever.
> If I recall correctly, in such cases we in PCIHP code we make
> such access a silent NOP. And tracing is there for a us
> to help figure out what's going on.
>
> 2nd:
> if it got this far, it means a device on a bus with bsel
> was found and we are completing cleanup. Error-ing out at
> this point will leak acpi_index.
The above two points seems to apply in this case as well and so should we
do this?
diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c
index 0fd0c1d811..c7692f5d5f 100644
--- a/hw/acpi/pcihp.c
+++ b/hw/acpi/pcihp.c
@@ -400,12 +400,6 @@ void acpi_pcihp_device_unplug_request_cb(HotplugHandler
*hotplug_dev,
trace_acpi_pci_unplug_request(bsel, slot);
- if (bsel < 0) {
- error_setg(errp, "Unsupported bus. Bus doesn't have property '"
- ACPI_PCIHP_PROP_BSEL "' set");
- return;
- }
-
s->acpi_pcihp_pci_status[bsel].down |= (1U << slot);
acpi_send_event(DEVICE(hotplug_dev), ACPI_PCI_HOTPLUG_STATUS);
}
I wanted to check before sending out a formal patch. I like symmetric
code.
