[PATCH-for-4.17] xen: fix generated code for calling hypercall handlers

[Juergen Gross <jgross@xxxxxxxx>]

The code generated for the call_handlers_*() macros needs to avoid
undefined behavior when multiple handlers share the same priority.
The issue is the hypercall number being unverified fed into the macros
and then used to set a mask via "mask = 1ULL << <hypercall-number>".

Avoid a shift amount of more than 63 by setting mask to zero in case
the hypercall number is too large.

Fixes: eca1f00d0227 ("xen: generate hypercall interface related code")
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 xen/scripts/gen_hypercall.awk | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/scripts/gen_hypercall.awk b/xen/scripts/gen_hypercall.awk
index 34840c514f..08b2f70bdb 100644
--- a/xen/scripts/gen_hypercall.awk
+++ b/xen/scripts/gen_hypercall.awk
@@ -263,7 +263,7 @@ END {
         printf("#define call_handlers_%s(num, ret, a1, a2, a3, a4, a5) \\\n", 
ca);
         printf("({ \\\n");
         if (need_mask)
-            printf("    uint64_t mask = 1ULL << num; \\\n");
+            printf("    uint64_t mask = (num > 63) ? 0 : 1ULL << num; \\\n");
         printf("    ");
         for (pl = 1; pl <= n_prios[ca]; pl++) {
             if (prios[ca, p_list[pl]] > 1) {
-- 
2.35.3