acpi: pcihp: fix left shift undefined behavior in acpi_pcihp_eject_slot()

Coverity spots subj in following guest triggered code path
  pci_write(, data = 0) -> acpi_pcihp_eject_slot(,slots = 0)
     uinst32_t slot = ctz32(slots)
     ...
     ... = ~(1U << slot)
where 'slot' value is 32 in case 'slots' bitmap is empty.
'slots' is a bitmap and empty one shouldn't  do anything
so return early doing nothing if resulted slot value is
not valid (i.e. not in 0-31 range)

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20200326135624.32464-1-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c
index 4dcef372bf..0dc963e983 100644
--- a/hw/acpi/pcihp.c
+++ b/hw/acpi/pcihp.c
@@ -154,7 +154,7 @@ static void acpi_pcihp_eject_slot(AcpiPciHpState *s, unsigned bsel, unsigned slo
 
     trace_acpi_pci_eject_slot(bsel, slot);
 
-    if (!bus) {
+    if (!bus || slot > 31) {
         return;
     }