patch "Drivers: hv: vmbus: Close timing hole that can corrupt per-cpu page" added to char-misc-testing

patch "Drivers: hv: vmbus: Close timing hole that can corrupt per-cpu page" added to char-misc-testing

[gregkh]

This is a note to let you know that I've just added the patch titled

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

to my char-misc git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-testing branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will be merged to the char-misc-next branch sometime soon,
after it passes testing, and the merge window is open.

If you have any questions about this process, please let me know.


>From 13b9abfc92be7c4454bff912021b9f835dea6e15 Mon Sep 17 00:00:00 2001
From: Michael Kelley <mikelley@microsoft.com>
Date: Thu, 18 May 2017 10:46:07 -0700
Subject: Drivers: hv: vmbus: Close timing hole that can corrupt per-cpu page

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.

Cc: <Stable@vger.kernel.org> #4.11
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>
---
 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 61fc8ce169a5..2ea12207caa0 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;
 }
 
-- 
2.13.0