Re: [PATCH v2 2/3] pci: sprinkle assert in PCI pin number

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Mar 23, 2021 at 10:24:30AM -0700, Isaku Yamahata wrote:
> If a device model
> (a) doesn't set the value to a correct interrupt number and then
> (b) triggers an interrupt for itself,
> it's device model bug. Add assert on interrupt pin number to catch
> this kind of bug more obviously.
> 
> Suggested-by: Peter Maydell <Peter.maydel@linaro.org>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> ---
>  hw/pci/pci.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> index ac9a24889c..cb6bab999b 100644
> --- a/hw/pci/pci.c
> +++ b/hw/pci/pci.c
> @@ -1450,6 +1450,8 @@ static void pci_irq_handler(void *opaque, int irq_num, int level)
>      PCIDevice *pci_dev = opaque;
>      int change;
>  
> +    assert(0 <= irq_num && irq_num < PCI_NUM_PINS);
> +    assert(level == 0 || level == 1);
>      change = level - pci_irq_state(pci_dev, irq_num);
>      if (!change)
>          return;
> @@ -1463,7 +1465,13 @@ static void pci_irq_handler(void *opaque, int irq_num, int level)
>  
>  static inline int pci_intx(PCIDevice *pci_dev)
>  {
> -    return pci_get_byte(pci_dev->config + PCI_INTERRUPT_PIN) - 1;
> +    int intx = pci_get_byte(pci_dev->config + PCI_INTERRUPT_PIN) - 1;




> +    /*
> +     * This function is used to setup/trigger irq.
> +     * So PIN = 0 (interrupt isn't used) doesn't make sense.

Well not really. It just returns it. But of course value -1 is not a
valid index.  Better: callers must make sure the device actually has an
interrupt pin, otherwise PCI_INTERRUPT_PIN is 0 and intx is negative
here.

> +     */
> +    assert(0 <= intx && intx < PCI_NUM_PINS);
> +    return intx;
>  }
>  
>  qemu_irq pci_allocate_irq(PCIDevice *pci_dev)
> -- 
> 2.25.1