From: Michael Kelley <mikelley@microsoft.com>
Date: Thu, 18 May 2017 10:46:07 -0700
Subject: [PATCH] Drivers: hv: vmbus: Close timing hole that can corrupt
 per-cpu page
References: bnc#1060662
Patch-mainline: 4.12.3
Git-commit: 13b9abfc92be7c4454bff912021b9f835dea6e15

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>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 drivers/hv/hv.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index 12e7baecb84e..f8c761fb71ad 100644
--- 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;
 }
 
-- 
2.14.2