[Qemu-devel] Re: [PATCH] pci: fix pci_default_read_config().

[Michael S. Tsirkin]

On Thu, May 27, 2010 at 02:44:42PM +0900, Isaku Yamahata wrote:
> address and config_size are both unsigned.
> So check which is bigger before minus operation.
> Otherwise the result of minus can be unexpected
> big value.
> 
> Signed-off-by: Isaku Yamahata <address@hidden>

An this happen in practice? If yes, how?

> ---
>  hw/pci.c |    9 +++++++--
>  1 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/pci.c b/hw/pci.c
> index 3362842..39a6206 100644
> --- a/hw/pci.c
> +++ b/hw/pci.c
> @@ -988,9 +988,14 @@ uint32_t pci_default_read_config(PCIDevice *d,
>                                   uint32_t address, int len)
>  {
>      uint32_t val = 0;
> +    uint32_t config_size = pci_config_size(d);
>      assert(len == 1 || len == 2 || len == 4);
> -    len = MIN(len, pci_config_size(d) - address);
> -    memcpy(&val, d->config + address, len);
> +    if (address < config_size) {
> +        len = MIN(len, config_size - address);
> +        memcpy(&val, d->config + address, len);
> +    } else {
> +        val = ~0;
> +    }
>      return le32_to_cpu(val);
>  }
>  
> -- 
> 1.6.6.1
>