[Xen-devel] [PATCH 1/8] xen/guest_access: Harden copy_to_guest_offset to prevent const dest operand

[Julien Grall <julien@xen.org>]

From: Julien Grall <jgrall@amazon.com>

At the moment, copy_to_guest_offset() will allow the hypervisor to copy
data to guest handle marked const.

Thankfully, no users of the helper will do that. Rather than hoping this
can be caught during review, harden copy_to_guest_offset() so the build
will fail if such users are introduced.

Signed-off-by: Julien Grall <jgrall@amazon.com>
---
 xen/include/asm-arm/guest_access.h | 2 +-
 xen/include/asm-x86/guest_access.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/include/asm-arm/guest_access.h b/xen/include/asm-arm/guest_access.h
index 8997a1cbfe..ff2eec237d 100644
--- a/xen/include/asm-arm/guest_access.h
+++ b/xen/include/asm-arm/guest_access.h
@@ -126,7 +126,7 @@ int access_guest_memory_by_ipa(struct domain *d, paddr_t ipa, void *buf,
 
 #define __copy_to_guest_offset(hnd, off, ptr, nr) ({    \
     const typeof(*(ptr)) *_s = (ptr);                   \
-    char (*_d)[sizeof(*_s)] = (void *)(hnd).p;          \
+    typeof(*((hnd).p)) *_d = (hnd).p;                   \
     ((void)((hnd).p == (ptr)));                         \
     __raw_copy_to_guest(_d+(off), _s, sizeof(*_s)*(nr));\
 })
diff --git a/xen/include/asm-x86/guest_access.h b/xen/include/asm-x86/guest_access.h
index ca700c959a..2693c6540b 100644
--- a/xen/include/asm-x86/guest_access.h
+++ b/xen/include/asm-x86/guest_access.h
@@ -86,7 +86,7 @@
  */
 #define copy_to_guest_offset(hnd, off, ptr, nr) ({      \
     const typeof(*(ptr)) *_s = (ptr);                   \
-    char (*_d)[sizeof(*_s)] = (void *)(hnd).p;          \
+    typeof(*((hnd).p)) *_d = (hnd).p;                   \
     ((void)((hnd).p == (ptr)));                         \
     raw_copy_to_guest(_d+(off), _s, sizeof(*_s)*(nr));  \
 })
-- 
2.17.1