[xen staging] include/public: add RING_RESPONSE_PROD_OVERFLOW macro

[patchbot@xxxxxxx]

commit d1f6296053f464c9da6f6fa5f1ece864130718ce
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Mon May 17 15:43:04 2021 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon May 17 15:43:04 2021 +0200

    include/public: add RING_RESPONSE_PROD_OVERFLOW macro
    
    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>
---
 xen/include/public/io/ring.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/xen/include/public/io/ring.h b/xen/include/public/io/ring.h
index 0b08b2697e..c486c457e0 100644
--- 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;                         \
--
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