Re: [PATCH 1/1] 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.

From: Stephen Hemminger
Date: Wed May 17 2017 - 18:00:28 EST


On Wed, 17 May 2017 14:40:55 -0700
mikelley@xxxxxxxxxxxxxxxxxxxxxx wrote:

> From: Michael Kelley <mikelley@xxxxxxxxxxxxx>
>
> Signed-off-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> ---
> drivers/hv/hv.c | 7 ++++++-
> 1 files changed, 6 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
> index 12e7bae..47ed538 100644
> --- a/drivers/hv/hv.c
> +++ b/drivers/hv/hv.c
> @@ -82,9 +82,14 @@ 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;
> }

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