linux-kernel - Re: [PATCH v2] rpmsg: virtio: don't let virtio core to validate used length

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Date:   Fri, 3 Dec 2021 15:34:33 +0100
From:   Arnaud POULIQUEN <arnaud.pouliquen@...s.st.com>
To:     Jason Wang <jasowang@...hat.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>
CC:     "Michael S. Tsirkin" <mst@...hat.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ohad Ben-Cohen <ohad@...ery.com>,
        <linux-remoteproc@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>
Subject: Re: [PATCH v2] rpmsg: virtio: don't let virtio core to validate used
 length



On 12/3/21 3:07 AM, Jason Wang wrote:
> On Fri, Dec 3, 2021 at 1:00 AM Mathieu Poirier
> <mathieu.poirier@...aro.org> wrote:
>>
>> Hey guys,
>>
>> On Thu, Nov 25, 2021 at 10:15:44AM +0800, Jason Wang wrote:
>>> On Thu, Nov 25, 2021 at 5:12 AM Michael S. Tsirkin <mst@...hat.com> wrote:
>>>>
>>>> On Wed, Nov 24, 2021 at 05:20:45PM +0100, Arnaud Pouliquen wrote:
>>>>> Using OpenAMP library on remote side, when the rpmsg framework tries to
>>>>> reuse the buffer the following error message is displayed in
>>>>> the virtqueue_get_buf_ctx_split function:
>>>>> "virtio_rpmsg_bus virtio0: output:used len 28 is larger than in buflen 0"
>>>>>
>>>>> As described in virtio specification:
>>>>> "many drivers ignored the len value, as a result, many devices set len
>>>>> incorrectly. Thus, when using the legacy interface, it is generally
>>>>> a good idea to ignore the len value in used ring entries if possible."
>>>>>
>>>>> To stay in compliance with the legacy libraries, this patch prevents the
>>>>> virtio core from validating used length.
>>>>>
>>>>> Fixes: 939779f5152d ("virtio_ring: validate used buffer length")
>>>>>
>>>>> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@...s.st.com>
>>>>> Cc: Jason Wang <jasowang@...hat.com>
>>>>> Cc: Michael S. Tsirkin <mst@...hat.com>
>>>>> ---
>>>>
>>>> Arnaud, thanks a lot for the analysis.
>>>>
>>>> Jason, I think this is another good point. We really should not
>>>> validate input for legacy devices at all.
>>>
>>> I agree. Will do that in the next version.
>>
>> I'm a little unclear about the "next version" in the above comment - is this
>> something I should wait for?  Should I move forward with Arnaud's patch?
> 
> Just to make it clear. If my understanding is correct, my series was
> reverted so this patch is not needed.

Indeed your patchset is no longer in the v5.16-rc3

Thanks,
Arnaud

> 
> For "next version", I meant I will resend the new version of used
> length validation that
> 
> - only do the validation when it was explicitly enabled
> - warn instead of bug
> - do not validate legacy device
> 
> Thanks
> 
>>
>> Thanks,
>> Mathieu
>>
>>>
>>> Thanks
>>>
>>>>
>>>>
>>>>> Update vs v1[1]: update commit message to clarify the context.
>>>>>
>>>>> base-commit: fa55b7dcdc43c1aa1ba12bca9d2dd4318c2a0dbf
>>>>>
>>>>> [1]https://lore.kernel.org/lkml/20211122160812.25125-1-arnaud.pouliquen@foss.st.com/T/
>>>>> ---
>>>>>  drivers/rpmsg/virtio_rpmsg_bus.c | 1 +
>>>>>  1 file changed, 1 insertion(+)
>>>>>
>>>>> diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
>>>>> index 9c112aa65040..5f73f19c2c38 100644
>>>>> --- a/drivers/rpmsg/virtio_rpmsg_bus.c
>>>>> +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
>>>>> @@ -1054,6 +1054,7 @@ static struct virtio_driver virtio_ipc_driver = {
>>>>>       .feature_table_size = ARRAY_SIZE(features),
>>>>>       .driver.name    = KBUILD_MODNAME,
>>>>>       .driver.owner   = THIS_MODULE,
>>>>> +     .suppress_used_validation = true,
>>>>>       .id_table       = id_table,
>>>>>       .probe          = rpmsg_probe,
>>>>>       .remove         = rpmsg_remove,
>>>>> --
>>>>> 2.17.1
>>>>
>>>
>>
>