[Xen-devel] [PATCH 1/2] x86/hvm: Add check when register io handler

[<suravee.suthikulpanit@xxxxxxx>]

From: Suravee Suthikulpanit <Suravee.Suthikulpanit@xxxxxxx>

At the time of registering HVM I/O handler, the HVM domain might
not have been initialized, which means the hvm_domain.io_handler
would be NULL. In the hvm_next_io_handler(), this should be checked
before returning and referencing the array. Also, the io_handler_count
should only be incremented on success.

So, this patch adds error handling in hvm_next_io_handler.

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
---
 xen/arch/x86/hvm/intercept.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/hvm/intercept.c b/xen/arch/x86/hvm/intercept.c
index 7096d74..13b81c9 100644
--- a/xen/arch/x86/hvm/intercept.c
+++ b/xen/arch/x86/hvm/intercept.c
@@ -248,14 +248,18 @@ int hvm_io_intercept(ioreq_t *p)
 
 struct hvm_io_handler *hvm_next_io_handler(struct domain *d)
 {
-    unsigned int i = d->arch.hvm_domain.io_handler_count++;
+    unsigned int i = d->arch.hvm_domain.io_handler_count;
 
-    if ( i == NR_IO_HANDLERS )
+    if ( !d->arch.hvm_domain.io_handler )
+        return NULL;
+
+    if ( i == NR_IO_HANDLERS - 1 )
     {
         domain_crash(d);
         return NULL;
     }
 
+    d->arch.hvm_domain.io_handler_count++;
     return &d->arch.hvm_domain.io_handler[i];
 }
 
-- 
1.9.1


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