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[PATCH] compat/memory: avoid UB shifts in XENMEM_exchange handling
- To: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 17 Apr 2025 16:08:31 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Manuel Andreas <manuel.andreas@xxxxxx>
- Delivery-date: Thu, 17 Apr 2025 14:08:51 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
Add an early basic check, yielding the same error code as the more
thorough on the the main handler would produce.
Fixes: b8a7efe8528a ("Enable compatibility mode operation for
HYPERVISOR_memory_op")
Reported-by: Manuel Andreas <manuel.andreas@xxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
--- a/xen/common/compat/memory.c
+++ b/xen/common/compat/memory.c
@@ -161,6 +161,11 @@ int compat_memory_op(unsigned int cmd, X
if ( copy_from_guest(&cmp.xchg, arg, 1) )
return -EFAULT;
+ /* Early coarse check, as max_order() isn't available here. */
+ if ( cmp.xchg.in.extent_order >= BITS_PER_INT ||
+ cmp.xchg.out.extent_order >= BITS_PER_INT )
+ return -EPERM;
+
order_delta = cmp.xchg.out.extent_order - cmp.xchg.in.extent_order;
/* Various sanity checks. */
if ( (cmp.xchg.nr_exchanged > cmp.xchg.in.nr_extents) ||
|
