Re: [PATCH] include/public: add RING_RESPONSE_PROD_OVERFLOW macro

[Jan Beulich <jbeulich@xxxxxxxx>]

On 12.05.2021 18:48, Juergen Gross wrote:
> Add a new RING_RESPONSE_PROD_OVERFLOW() macro for being able to
> detect an ill-behaved backend tampering with the response producer
> index.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

> --- a/xen/include/public/io/ring.h
> +++ b/xen/include/public/io/ring.h
> @@ -259,6 +259,10 @@ typedef struct __name##_back_ring __name##_back_ring_t
>  #define RING_REQUEST_PROD_OVERFLOW(_r, _prod)                           \
>      (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r))
>  
> +/* Ill-behaved backend determination: Can there be this many responses? */
> +#define RING_RESPONSE_PROD_OVERFLOW(_r, _prod)                          \
> +    (((_prod) - (_r)->rsp_cons) > RING_SIZE(_r))
> +
>  #define RING_PUSH_REQUESTS(_r) do {                                     \
>      xen_wmb(); /* back sees requests /before/ updated producer index */ \
>      (_r)->sring->req_prod = (_r)->req_prod_pvt;                         \
>