Drivers: hv: vmbus: Close timing hole that can corrupt per-cpu page

commit 13b9abfc92be7c4454bff912021b9f835dea6e15 upstream.

Extend the disabling of preemption to include the hypercall so that
another thread can't get the CPU and corrupt the per-cpu page used
for hypercall arguments.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index 665a64f1611e31fe3650f6d030aa373ca1301c03..a87bdc22f82c4d26d6a47e725c46a872bff9c99c 100644 (file)
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -82,10 +82,15 @@ int hv_post_message(union hv_connection_id connection_id,
        aligned_msg->message_type = message_type;
        aligned_msg->payload_size = payload_size;
        memcpy((void *)aligned_msg->payload, payload, payload_size);
-       put_cpu_ptr(hv_cpu);
 
        status = hv_do_hypercall(HVCALL_POST_MESSAGE, aligned_msg, NULL);
 
+       /* Preemption must remain disabled until after the hypercall
+        * so some other thread can't get scheduled onto this cpu and
+        * corrupt the per-cpu post_msg_page
+        */
+       put_cpu_ptr(hv_cpu);
+
        return status & 0xFFFF;
 }