Re: [PATCH for-next 0/4] RDMA/hns: Introduce delay-destruction mechanism

[Junxian Huang <huangjunxian6@hisilicon.com>]

On 2025/2/20 17:08, Leon Romanovsky wrote:
> On Thu, Feb 20, 2025 at 04:45:54PM +0800, Junxian Huang wrote:
>>
>>
>> On 2025/2/20 15:32, Leon Romanovsky wrote:
>>> On Thu, Feb 20, 2025 at 11:48:49AM +0800, Junxian Huang wrote:
>>>>
>>>>
>>>> On 2025/2/19 22:35, Leon Romanovsky wrote:
>>>>> On Wed, Feb 19, 2025 at 09:07:36PM +0800, Junxian Huang wrote:
>>>>>>
>>>>>>
>>>>>> On 2025/2/19 20:14, Leon Romanovsky wrote:
>>>>>>> On Mon, Feb 17, 2025 at 03:01:19PM +0800, Junxian Huang wrote:
>>>>>>>> When mailboxes for resource(QP/CQ/SRQ) destruction fail, it's unable
>>>>>>>> to notify HW about the destruction. In this case, driver will still
>>>>>>>> free the resources, while HW may still access them, thus leading to
>>>>>>>> a UAF.
>>>>>>>
>>>>>>>> This series introduces delay-destruction mechanism to fix such HW UAF,
>>>>>>>> including thw HW CTX and doorbells.
>>>>>>>
>>>>>>> And why can't you fix FW instead?
>>>>>>>
>>>>>>
>>>>>> The key is the failure of mailbox, and there are some cases that would
>>>>>> lead to it, which we don't really consider as FW bugs.
>>>>>>
>>>>>> For example, when some random fatal error like RAS error occurs in FW,
>>>>>> our FW will be reset. Driver's mailbox will fail during the FW reset.
>>>>>
>>>>> I don't understand this scenario. You said at the beginning that HW can
>>>>> access host memory and this triggers UAF. However now, you are presenting 
>>>>> case where driver tries to access mailbox.
>>>>>
>>>>
>>>> No, I'm saying that mailbox errors are the reason of HW UAF. Let me
>>>> explain this scenario in more detail.
>>>>
>>>> Driver notifies HW about the memory release with mailbox. The procedure
>>>> of a mailbox is:
>>>> 	a) driver posts the mailbox to FW
>>>> 	b) FW writes the mailbox data into HW
>>>>
>>>> In this scenario, step a) will fail due to the FW reset, HW won't get
>>>> notified and thus may lead to UAF.
>>>
>>> Exactly, FW performed reset and didn't prevent from HW to access it.
>>>
>>
>> Yes, but the problem is that our HW doesn't provide a method to prevent
>> the access. There's nothing FW can do in this scenario, so we can only
>> prevent UAF by adding these codes in driver.
> 
> Somehow HW doesn't access mailbox if destroy was successful, so why
> can't FW use same "method" to inform HW before reset?
> 

Mailbox carries information of the specific resource (QP/CQ/SRQ/MR)
that are being destroyed. It's impossible for FW to predict which
QP/CQ/SRQ/MR will be destroyed by driver during reset before the
reset starts.

Thanks,
Junxian

> Thanks