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

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Date:   Tue, 10 Sep 2019 09:52:10 +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 2019/9/9 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>



>