Re: [PATCH 1/1] vfio: ccw: fix bad ptr math for TIC cda translation

[Cornelia Huck <cohuck@redhat.com>]

On Thu, 20 Jul 2017 05:19:50 +0200
Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com> wrote:

> From: "Jason J. Herne" <jjherne@linux.vnet.ibm.com>
> 
> When we are translating channel data addresses from guest to host
> address space for TIC instructions we are getting incorrect
> addresses because of a pointer arithmetic error.

Ah, so you saw actual failures?

> 
> We currently calculate the offset of the TIC's cda from the start
> of the channel program chain (ccw->cda - ccw_head). We then add
> that to the address of the ccw chain in host memory (iter->ch_ccw).
> The problem is that iter->ch_ccw is a poiner to struct ccw1 so
> when we increment it we are actually incrementing by the size of
> struct ccw1 which is 8 bytes. The intent was to increment by
> n-bytes, not n*8.
> 
> The fix: cast iter->ch_ccw to char* so it will be incremented by
> n*1.
> 
> Reviewed-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
> Signed-off-by: Jason J. Herne <jjherne@linux.vnet.ibm.com>

Please add your s-o-b if you send out patches, otherwise I cannot apply
them, sorry.

> ---
>  drivers/s390/cio/vfio_ccw_cp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
> index ba6ac83a6c25..5ccfdc80d0ec 100644
> --- a/drivers/s390/cio/vfio_ccw_cp.c
> +++ b/drivers/s390/cio/vfio_ccw_cp.c
> @@ -481,7 +481,7 @@ static int ccwchain_fetch_tic(struct ccwchain *chain,
>  		ccw_tail = ccw_head + (iter->ch_len - 1) * sizeof(struct ccw1);
>  
>  		if ((ccw_head <= ccw->cda) && (ccw->cda <= ccw_tail)) {
> -			ccw->cda = (__u32) (addr_t) (iter->ch_ccw +
> +			ccw->cda = (__u32) (addr_t) (((char *)iter->ch_ccw) +
>  						     (ccw->cda - ccw_head));
>  			return 0;
>  		}