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

[<gregkh@linuxfoundation.org>]

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-next 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 also be merged in the next major kernel release
during the merge window.

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