[xen staging] xen: re-add type checking to {,__}copy_from_guest_offset()

[patchbot@xxxxxxx]

commit 735865f88486814dd6ae255f13a7f70cd3b01d4f
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Jun 25 11:36:59 2024 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jun 25 11:36:59 2024 +0200

    xen: re-add type checking to {,__}copy_from_guest_offset()
    
    When re-working them to avoid UB on guest address calculations, I failed
    to add explicit type checks in exchange for the implicit ones that until
    then had happened in assignments that were there anyway.
    
    Fixes: 43d5c5d5f70b ("xen: avoid UB in guest handle arithmetic")
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
 xen/include/xen/guest_access.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/xen/include/xen/guest_access.h b/xen/include/xen/guest_access.h
index 96dbef2e02..a2146749e3 100644
--- a/xen/include/xen/guest_access.h
+++ b/xen/include/xen/guest_access.h
@@ -86,6 +86,7 @@
 #define copy_from_guest_offset(ptr, hnd, off, nr) ({    \
     unsigned long s_ = (unsigned long)(hnd).p;          \
     typeof(*(ptr)) *_d = (ptr);                         \
+    (void)((hnd).p == _d);                              \
     raw_copy_from_guest(_d,                             \
                         (const void *)(s_ + (off) * sizeof(*_d)), \
                         (nr) * sizeof(*_d));            \
@@ -140,6 +141,7 @@
 #define __copy_from_guest_offset(ptr, hnd, off, nr) ({          \
     unsigned long s_ = (unsigned long)(hnd).p;                  \
     typeof(*(ptr)) *_d = (ptr);                                 \
+    (void)((hnd).p == _d);                                      \
     __raw_copy_from_guest(_d,                                   \
                           (const void *)(s_ + (off) * sizeof(*_d)), \
                           (nr) * sizeof(*_d));                  \
--
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