linux-kernel - Re: [PATCH] vp_vdpa: harden the logic of set status

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Message-ID: <11062911-270a-6018-34a4-8edd50674999@redhat.com>
Date:   Mon, 14 Nov 2022 12:21:28 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@...wei.com>, Stefano Garzarella <sgarzare@...hat.com>
Cc:     stefanha@...hat.com, mst@...hat.com,
        virtualization@...ts.linux-foundation.org, arei.gonglei@...wei.com,
        yechuan@...wei.com, huangzhichao@...wei.com,
        linux-kernel@...r.kernel.org, xiehong@...wei.com
Subject: Re: [PATCH] vp_vdpa: harden the logic of set status


在 2022/11/12 15:33, Longpeng (Mike, Cloud Infrastructure Service Product 
Dept.) 写道:
>
>
> 在 2022/11/12 0:35, Stefano Garzarella 写道:
>> On Fri, Nov 11, 2022 at 11:49:10PM +0800, Longpeng (Mike, Cloud 
>> Infrastructure Service Product Dept.) wrote:
>>>
>>>
>>> 在 2022/11/11 23:14, Stefano Garzarella 写道:
>>>> On Fri, Nov 11, 2022 at 10:55:05PM +0800, Longpeng(Mike) wrote:
>>>>> From: Longpeng <longpeng2@...wei.com>
>>>>>
>>>>> 1. We should not set status to 0 when invoking vp_vdpa_set_status().
>>>>>
>>>>> 2. The driver MUST wait for a read of device_status to return 0 
>>>>> before
>>>>>   reinitializing the device.
>>>>>
>>>>> Signed-off-by: Longpeng <longpeng2@...wei.com>
>>>>> ---
>>>>> drivers/vdpa/virtio_pci/vp_vdpa.c | 11 ++++++++++-
>>>>> 1 file changed, 10 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/vdpa/virtio_pci/vp_vdpa.c 
>>>>> b/drivers/vdpa/virtio_pci/vp_vdpa.c
>>>>> index d448db0c4de3..d35fac5cde11 100644
>>>>> --- a/drivers/vdpa/virtio_pci/vp_vdpa.c
>>>>> +++ b/drivers/vdpa/virtio_pci/vp_vdpa.c
>>>>> @@ -212,8 +212,12 @@ static void vp_vdpa_set_status(struct 
>>>>> vdpa_device *vdpa, u8 status)
>>>>> {
>>>>>     struct vp_vdpa *vp_vdpa = vdpa_to_vp(vdpa);
>>>>>     struct virtio_pci_modern_device *mdev = vp_vdpa_to_mdev(vp_vdpa);
>>>>> -    u8 s = vp_vdpa_get_status(vdpa);
>>>>
>>>> Is this change really needed?
>>>>
>>> No need to get the status if we try to set status to 0 (trigger BUG).
>>>
>>
>> Okay, but that's the case that should never happen, so IMHO we can 
>> leave it as it is.
>>
> OK.
>
>>>>> +    u8 s;
>>>>> +
>>>>> +    /* We should never be setting status to 0. */
>>>>> +    BUG_ON(status == 0);
>>>>
>>>> IMHO panicking the kernel seems excessive in this case, please use 
>>>> WARN_ON and maybe return earlier.
>>>>
>>> Um...I referenced the vp_reset/vp_set_status,
>>
>> Ah I see, maybe it's an old code, because recently we always try to 
>> avoid BUG_ON().
>>
> OK. The checkpatch.pl script also triggered a waring about it.
> I'll use WARN_ON in next version.
>
>>>
>>>>>
>>>>> +    s = vp_vdpa_get_status(vdpa);
>>>>>     if (status & VIRTIO_CONFIG_S_DRIVER_OK &&
>>>>>         !(s & VIRTIO_CONFIG_S_DRIVER_OK)) {
>>>>>         vp_vdpa_request_irq(vp_vdpa);
>>>>> @@ -229,6 +233,11 @@ static int vp_vdpa_reset(struct vdpa_device 
>>>>> *vdpa)
>>>>>     u8 s = vp_vdpa_get_status(vdpa);
>>>>>
>>>>>     vp_modern_set_status(mdev, 0);
>>>>> +    /* After writing 0 to device_status, the driver MUST wait for 
>>>>> a read of
>>>>> +     * device_status to return 0 before reinitializing the device.
>>>>> +     */
>>>>> +    while (vp_modern_get_status(mdev))
>>>>> +        msleep(1);
>>>>
>>>> Should we set a limit after which we give up? A malfunctioning 
>>>> device could keep us here forever.
>>>>
>>> Yes, but the malfunctioning device maybe can not work anymore, how 
>>> to handle it?
>>
>> Maybe we should set the status to broken, but in this case we could 
>> just return an error if we couldn't reset it, how about that?
>>
> It can work, but it seems to violate the specification. Maybe we can 
> also wait for other guys' suggestions and then decide how to handle 
> the exception.


Need more thought but it's not an issue that is introduced in this 
patch, we can do optimization on top.

Probably a warning plus FAILED. Then at least the device can DOS the 
driver which is good for hardening as well.

Thanks


>
>> Thanks,
>> Stefano
>>
>> .
>