netdev - Re: [PATCH V3 1/6] vDPA/ifcvf: get_config_size should return a value no greater than dev implementation

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Date:   Wed, 13 Jul 2022 15:52:06 +0800
From:   "Zhu, Lingshan" <lingshan.zhu@...el.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        netdev <netdev@...r.kernel.org>, Parav Pandit <parav@...dia.com>,
        Yongji Xie <xieyongji@...edance.com>,
        "Dawar, Gautam" <gautam.dawar@....com>
Subject: Re: [PATCH V3 1/6] vDPA/ifcvf: get_config_size should return a value
 no greater than dev implementation



On 7/13/2022 1:44 PM, Michael S. Tsirkin wrote:
> On Fri, Jul 08, 2022 at 02:44:08PM +0800, Zhu, Lingshan wrote:
>>
>> On 7/4/2022 12:39 PM, Jason Wang wrote:
>>> On Fri, Jul 1, 2022 at 9:36 PM Zhu Lingshan <lingshan.zhu@...el.com> wrote:
>>>> ifcvf_get_config_size() should return a virtio device type specific value,
>>>> however the ret_value should not be greater than the onboard size of
>>>> the device implementation. E.g., for virtio_net, config_size should be
>>>> the minimum value of sizeof(struct virtio_net_config) and the onboard
>>>> cap size.
>>> Rethink of this, I wonder what's the value of exposing device
>>> implementation details to users? Anyhow the parent is in charge of
>>> "emulating" config space accessing.
>> This will not be exposed to the users, it is a ifcvf internal helper,
>> to get the actual device config space size.
>>
>> For example, if ifcvf drives an Intel virtio-net device,
>> if the device config space size is greater than sizeof(struct
>> virtio_net_cfg),
>> this means the device has something more than the spec, some private fields,
>> we don't want to expose these extra private fields to the users, so in this
>> case,
>> we only return what the spec defines.
> This is kind of already the case.
>
>> If the device config space size is less than sizeof(struct virtio_net_cfg),
>> means the device didn't implement all fields the spec defined, like no RSS.
>> In such cases, we only return what the device implemented.
>> So these are defensive programming.
> I think the issue you are describing is simply this.
>
>
> Driver must not access BAR outside capability length. Current code
> does not verify that it does not. Not the case for the current
> devices but it's best to be safe against the case where
> device does not implement some of the capability.
>
>
>  From that POV I think the patch is good, just fix the log.
sure, I will do

Thanks,
Zhu Lingshan
>
>
>
>>> If we do this, it's probably a blocker for cross vendor stuff.
>>>
>>> Thanks
>>>
>>>> Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
>>>> ---
>>>>    drivers/vdpa/ifcvf/ifcvf_base.c | 13 +++++++++++--
>>>>    drivers/vdpa/ifcvf/ifcvf_base.h |  2 ++
>>>>    2 files changed, 13 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/vdpa/ifcvf/ifcvf_base.c b/drivers/vdpa/ifcvf/ifcvf_base.c
>>>> index 48c4dadb0c7c..fb957b57941e 100644
>>>> --- a/drivers/vdpa/ifcvf/ifcvf_base.c
>>>> +++ b/drivers/vdpa/ifcvf/ifcvf_base.c
>>>> @@ -128,6 +128,7 @@ int ifcvf_init_hw(struct ifcvf_hw *hw, struct pci_dev *pdev)
>>>>                           break;
>>>>                   case VIRTIO_PCI_CAP_DEVICE_CFG:
>>>>                           hw->dev_cfg = get_cap_addr(hw, &cap);
>>>> +                       hw->cap_dev_config_size = le32_to_cpu(cap.length);
>>>>                           IFCVF_DBG(pdev, "hw->dev_cfg = %p\n", hw->dev_cfg);
>>>>                           break;
>>>>                   }
>>>> @@ -233,15 +234,23 @@ int ifcvf_verify_min_features(struct ifcvf_hw *hw, u64 features)
>>>>    u32 ifcvf_get_config_size(struct ifcvf_hw *hw)
>>>>    {
>>>>           struct ifcvf_adapter *adapter;
>>>> +       u32 net_config_size = sizeof(struct virtio_net_config);
>>>> +       u32 blk_config_size = sizeof(struct virtio_blk_config);
>>>> +       u32 cap_size = hw->cap_dev_config_size;
>>>>           u32 config_size;
>>>>
>>>>           adapter = vf_to_adapter(hw);
>>>> +       /* If the onboard device config space size is greater than
>>>> +        * the size of struct virtio_net/blk_config, only the spec
>>>> +        * implementing contents size is returned, this is very
>>>> +        * unlikely, defensive programming.
>>>> +        */
>>>>           switch (hw->dev_type) {
>>>>           case VIRTIO_ID_NET:
>>>> -               config_size = sizeof(struct virtio_net_config);
>>>> +               config_size = cap_size >= net_config_size ? net_config_size : cap_size;
>>>>                   break;
>>>>           case VIRTIO_ID_BLOCK:
>>>> -               config_size = sizeof(struct virtio_blk_config);
>>>> +               config_size = cap_size >= blk_config_size ? blk_config_size : cap_size;
>>>>                   break;
>>>>           default:
>>>>                   config_size = 0;
>>>> diff --git a/drivers/vdpa/ifcvf/ifcvf_base.h b/drivers/vdpa/ifcvf/ifcvf_base.h
>>>> index 115b61f4924b..f5563f665cc6 100644
>>>> --- a/drivers/vdpa/ifcvf/ifcvf_base.h
>>>> +++ b/drivers/vdpa/ifcvf/ifcvf_base.h
>>>> @@ -87,6 +87,8 @@ struct ifcvf_hw {
>>>>           int config_irq;
>>>>           int vqs_reused_irq;
>>>>           u16 nr_vring;
>>>> +       /* VIRTIO_PCI_CAP_DEVICE_CFG size */
>>>> +       u32 cap_dev_config_size;
>>>>    };
>>>>
>>>>    struct ifcvf_adapter {
>>>> --
>>>> 2.31.1
>>>>