[PATCH] xen/ubsan: Fix UB in type_descriptor declaration

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

struct type_descriptor is arranged with a NUL terminated string following the
kind/info fields.

The only reason this doesn't trip UBSAN detection itself (on more modern
compilers at least) is because struct type_descriptor is only referenced in
suppressed regions.

Switch the declaration to be a real flexible member.  No functional change.

Fixes: 00fcf4dd8eb4 ("xen/ubsan: Import ubsan implementation from Linux 4.13")
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: George Dunlap <George.Dunlap@xxxxxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Julien Grall <julien@xxxxxxx>
CC: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>

For 4.19, and for backport to all reasonable versions.  This bug deserves some
kind of irony award.
---
 xen/common/ubsan/ubsan.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/common/ubsan/ubsan.h b/xen/common/ubsan/ubsan.h
index a3159040fefb..3db42e75b138 100644
--- a/xen/common/ubsan/ubsan.h
+++ b/xen/common/ubsan/ubsan.h
@@ -10,7 +10,7 @@ enum {
 struct type_descriptor {
        u16 type_kind;
        u16 type_info;
-       char type_name[1];
+       char type_name[];
 };
 
 struct source_location {

base-commit: 8b4243a9b560c89bb259db5a27832c253d4bebc7
-- 
2.39.2