linux-kernel - 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.

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Date:   Wed, 17 May 2017 15:04:54 -0700
From:   "Joshua R. Poulson" <jrp@....org>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     mikelley@...hange.microsoft.com, mikelley@...rosoft.com,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
        Vitaly Kuznetsov <vkuznets@...hat.com>, jasowang@...hat.com,
        leann.ogasawara@...onical.com, marcelo.cerri@...onical.com,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>
Subject: 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.

This looks like a bugfix that should be included in stable.

On Wed, May 17, 2017 at 3:00 PM, Stephen Hemminger
<stephen@...workplumber.org> wrote:
> On Wed, 17 May 2017 14:40:55 -0700
> mikelley@...hange.microsoft.com wrote:
>
>> From: Michael Kelley <mikelley@...rosoft.com>
>>
>> Signed-off-by: Michael Kelley <mikelley@...rosoft.com>
>> ---
>>  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;
>>  }
>
> Since Subject line becomes the git log description, it is best practice to keep it short.
> On git commit man page:
>
>        Though not required, it’s a good idea to begin the commit message with
>        a single short (less than 50 character) line summarizing the change,
>        followed by a blank line and then a more thorough description.
>
> If you need to provide more description put it in the message body.