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

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

[Igor Mammedov]

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>
---
 hw/acpi/pcihp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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;
     }
 
-- 
2.18.1

Re: [PATCH] acpi: pcihp: fix left shift undefined behavior in acpi_pcihp_eject_slot()

[Michael S. Tsirkin]

On Thu, Mar 26, 2020 at 09:56:24AM -0400, Igor Mammedov wrote:
> 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>

tagged, thanks!

> ---
>  hw/acpi/pcihp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> 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;
>      }
>  
> -- 
> 2.18.1