linux-kernel - Re: [RFC PATCH untested] vhost: block speculation of translated descriptors

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Message-ID: <bb71974e-a8b3-4cc4-f3e1-e48118469b78@redhat.com>
Date:   Tue, 10 Sep 2019 15:28:27 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [RFC PATCH untested] vhost: block speculation of translated
 descriptors


On 2019/9/10 下午2:48, Michael S. Tsirkin wrote:
> On Tue, Sep 10, 2019 at 09:52:10AM +0800, Jason Wang wrote:
>> On 2019/9/9 下午10:45, Michael S. Tsirkin wrote:
>>> On Mon, Sep 09, 2019 at 03:19:55PM +0800, Jason Wang wrote:
>>>> On 2019/9/8 下午7:05, Michael S. Tsirkin wrote:
>>>>> iovec addresses coming from vhost are assumed to be
>>>>> pre-validated, but in fact can be speculated to a value
>>>>> out of range.
>>>>>
>>>>> Userspace address are later validated with array_index_nospec so we can
>>>>> be sure kernel info does not leak through these addresses, but vhost
>>>>> must also not leak userspace info outside the allowed memory table to
>>>>> guests.
>>>>>
>>>>> Following the defence in depth principle, make sure
>>>>> the address is not validated out of node range.
>>>>>
>>>>> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
>>>>> ---
>>>>>     drivers/vhost/vhost.c | 4 +++-
>>>>>     1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>>>>> index 5dc174ac8cac..0ee375fb7145 100644
>>>>> --- a/drivers/vhost/vhost.c
>>>>> +++ b/drivers/vhost/vhost.c
>>>>> @@ -2072,7 +2072,9 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len,
>>>>>     		size = node->size - addr + node->start;
>>>>>     		_iov->iov_len = min((u64)len - s, size);
>>>>>     		_iov->iov_base = (void __user *)(unsigned long)
>>>>> -			(node->userspace_addr + addr - node->start);
>>>>> +			(node->userspace_addr +
>>>>> +			 array_index_nospec(addr - node->start,
>>>>> +					    node->size));
>>>>>     		s += size;
>>>>>     		addr += size;
>>>>>     		++ret;
>>>> I've tried this on Kaby Lake smap off metadata acceleration off using
>>>> testpmd (virtio-user) + vhost_net. I don't see obvious performance
>>>> difference with TX PPS.
>>>>
>>>> Thanks
>>> Should I push this to Linus right now then? It's a security thing so
>>> maybe we better do it ASAP ... what's your opinion?
>>
>> Yes, you can.
>>
>> Acked-by: Jason Wang <jasowang@...hat.com>
>
> And should I include
>
> Tested-by: Jason Wang <jasowang@...hat.com>
>
> ?


Yes.

Thanks


>
>>