Re: [PATCH] pci: assert configuration access is within bounds

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* P J P (ppandit@redhat.com) wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
> 
> While accessing PCI configuration bytes, assert that
> 'address + len' is within PCI configuration space.
> 
> Generally it is within bounds. This is more of a defensive
> assert, in case a buggy device was to send 'address' which
> may go out of bounds.

Can a guest trigger this assert?

Dave

> Suggested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  hw/pci/pci.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> Update v1: defensive assert as separate patch
>   -> https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg00957.html
>   -> https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg00960.html
> 
> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> index 70c66965f5..7bf2ae6d92 100644
> --- a/hw/pci/pci.c
> +++ b/hw/pci/pci.c
> @@ -1381,6 +1381,8 @@ uint32_t pci_default_read_config(PCIDevice *d,
>  {
>      uint32_t val = 0;
>  
> +    assert(address + len <= pci_config_size(d));
> +
>      if (pci_is_express_downstream_port(d) &&
>          ranges_overlap(address, len, d->exp.exp_cap + PCI_EXP_LNKSTA, 2)) {
>          pcie_sync_bridge_lnk(d);
> @@ -1394,6 +1396,8 @@ void pci_default_write_config(PCIDevice *d, uint32_t addr, uint32_t val_in, int
>      int i, was_irq_disabled = pci_irq_disabled(d);
>      uint32_t val = val_in;
>  
> +    assert(addr + l <= pci_config_size(d));
> +
>      for (i = 0; i < l; val >>= 8, ++i) {
>          uint8_t wmask = d->wmask[addr + i];
>          uint8_t w1cmask = d->w1cmask[addr + i];
> -- 
> 2.26.2
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK