Re: [PATCH] msix: add valid.accepts methods to check address

[Philippe Mathieu-Daudé]

On 6/1/20 7:14 AM, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
> 
> While doing msi-x mmio operations, a guest may send an address
> that leads to an OOB access issue. Add valid.accepts methods to
> ensure that ensuing mmio r/w operation don't go beyond regions.
> 

Fixes: CVE-2020-xxxxx

> Reported-by: Ren Ding <rding@gatech.edu>
> Reported-by: Hanqing Zhao <hanqing@gatech.edu>
> Reported-by: Anatoly Trosinenko <anatoly.trosinenko@gmail.com>
> Reported-by: Alexander Bulekov <alxndr@bu.edu>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  hw/pci/msix.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/hw/pci/msix.c b/hw/pci/msix.c
> index 29187898f2..d90d66a3b8 100644
> --- a/hw/pci/msix.c
> +++ b/hw/pci/msix.c
> @@ -193,6 +193,15 @@ static void msix_table_mmio_write(void *opaque, hwaddr 
> addr,
>      msix_handle_mask_update(dev, vector, was_masked);
>  }
>  
> +static bool msix_table_accepts(void *opaque, hwaddr addr, unsigned size,
> +                                    bool is_write, MemTxAttrs attrs)
> +{
> +    PCIDevice *dev = opaque;
> +    uint16_t tbl_size = dev->msix_entries_nr * PCI_MSIX_ENTRY_SIZE;
> +
> +    return dev->msix_table + addr + 4 <= dev->msix_table + tbl_size;

Can be simplified as:

       return addr + 4 <= dev->msix_entries_nr * PCI_MSIX_ENTRY_SIZE;

> +}
> +
>  static const MemoryRegionOps msix_table_mmio_ops = {
>      .read = msix_table_mmio_read,
>      .write = msix_table_mmio_write,
> @@ -200,6 +209,7 @@ static const MemoryRegionOps msix_table_mmio_ops = {
>      .valid = {
>          .min_access_size = 4,
>          .max_access_size = 4,
> +        .accepts = msix_table_accepts
>      },
>  };
>  
> @@ -221,6 +231,15 @@ static void msix_pba_mmio_write(void *opaque, hwaddr 
> addr,
>  {
>  }
>  
> +static bool msix_pba_accepts(void *opaque, hwaddr addr, unsigned size,
> +                                    bool is_write, MemTxAttrs attrs)
> +{
> +    PCIDevice *dev = opaque;
> +    uint16_t pba_size = QEMU_ALIGN_UP(dev->msix_entries_nr, 64) / 8;
> +
> +    return dev->msix_pba + addr + 4 <= dev->msix_pba + pba_size;

Can be simplified as:

       return addr + 4 <= QEMU_ALIGN_UP(dev->msix_entries_nr, 64) / 8;

> +}
> +
>  static const MemoryRegionOps msix_pba_mmio_ops = {
>      .read = msix_pba_mmio_read,
>      .write = msix_pba_mmio_write,
> @@ -228,6 +247,7 @@ static const MemoryRegionOps msix_pba_mmio_ops = {
>      .valid = {
>          .min_access_size = 4,
>          .max_access_size = 4,
> +        .accepts = msix_pba_accepts
>      },
>  };
>  
>