Re: [Qemu-devel] [PATCH] spapr_vty: lookup should only return valid VTY objects

[David Gibson <david@gibson.dropbear.id.au>]

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Ugh, sorry, this version is buggy, I'll resend.

On Wed, Jul 01, 2015 at 01:51:43PM +1000, David Gibson wrote:
> From: Greg Kurz <gkurz@linux.vnet.ibm.com>
> 
> If a guest passes the reg property of a valid VIO object that is not a VTY
> to either H_GET_TERM_CHAR or H_PUT_TERM_CHAR, QEMU hits a dynamic cast
> assertion and aborts.
> 
> PAPR+ says "Hypervisor checks the termno parameter for validity against the
> Vterm IOA unit addresses assigned to the partition, else return H_Parameter."
> 
> This patch adds a type check to ensure vty_lookup() either returns a pointer
> to a valid VTY object or NULL.  H_GET_TERM_CHAR and H_PUT_TERM_CHAR will
> now return H_PARAMETER to the guest instead of crashing.
> 
> The patch has no effect on the reg == 0 hack used to implement the RTAS call
> display-character.
> 
> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  hw/char/spapr_vty.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> I've already merged this into spapr-next and it will be in the next
> batch I send if not merged before that.
> 
> But I think this is an important enough fix (it allows the guest to
> crash qemu) that it should probably be fastracked into mainline and
> stable.
> 
> diff --git a/hw/char/spapr_vty.c b/hw/char/spapr_vty.c
> index 1d53035..f407cd0 100644
> --- a/hw/char/spapr_vty.c
> +++ b/hw/char/spapr_vty.c
> @@ -228,7 +228,7 @@ VIOsPAPRDevice *vty_lookup(sPAPRMachineState *spapr, target_ulong reg)
>          return spapr_vty_get_default(spapr->vio_bus);
>      }
>  
> -    return sdev;
> +    return object_dynamic_cast(sdev, TYPE_VIO_SPAPR_VTY_DEVICE);
>  }
>  
>  static void spapr_vty_register_types(void)

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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