Re: [Xen-devel] [PATCH v1 03/10] xen/pt: Check if reg->init function sets the 'data' past the reg->size

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 2 Jul 2015, Konrad Rzeszutek Wilk wrote:
> It should never happen, but in case it does (an developer adds
> a new register and the 'init_val' expands past the register
> size) we want to report. The code will only write up to
> reg->size so there is no runtime danger of the register spilling
> across other ones - however to catch this sort of thing
> we still return an error.
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
>  hw/xen/xen_pt_config_init.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/xen/xen_pt_config_init.c b/hw/xen/xen_pt_config_init.c
> index 3938afd..09309ba 100644
> --- a/hw/xen/xen_pt_config_init.c
> +++ b/hw/xen/xen_pt_config_init.c
> @@ -1904,9 +1904,15 @@ static int 
> xen_pt_config_reg_init(XenPCIPassthroughState *s,
>          } else
>              val = data;
>  
> +        if (val & ~size_mask) {
> +            XEN_PT_ERR(&s->dev,"Offset 0x%04x:0x%04x expands past register 
> size(%d)!\n",
> +                       offset, val, reg->size);
> +            g_free(reg_entry);
> +            return -ENXIO;
> +        }

If we worry about changes to init_val, wouldn't it be better to add
QEMU_BUILD_BUG_ON(data & ~size_mask)?


>          /* This could be just pci_set_long as we don't modify the bits
> -         * past reg->size, but in case this routine is run in parallel
> -         * we do not want to over-write other registers. */
> +         * past reg->size, but in case this routine is run in parallel or the
> +         * init value is larger, we do not want to over-write registers. */
>          switch (reg->size) {
>          case 1: pci_set_byte(s->dev.config + offset, (uint8_t)val); break;
>          case 2: pci_set_word(s->dev.config + offset, (uint16_t)val); break;
> -- 
> 2.1.0
> 

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