Linux Virtualization - Sep 2019 - [RFC PATCH untested] vhost: block speculation of translated descriptors

On Mon, Sep 09, 2019 at 03:19:55PM +0800, Jason Wang
wrote:
> 
> On 2019/9/8 ??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 at redhat.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?

-- 
MST

On 2019/9/9 ??10:45, Michael S. Tsirkin wrote:
> On Mon, Sep 09, 2019 at 03:19:55PM +0800, Jason Wang wrote:
>> On 2019/9/8 ??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 at redhat.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 at redhat.com>


>

On Tue, Sep 10, 2019 at 09:52:10AM +0800, Jason Wang
wrote:
> 
> On 2019/9/9 ??10:45, Michael S. Tsirkin wrote:
> > On Mon, Sep 09, 2019 at 03:19:55PM +0800, Jason Wang wrote:
> > > On 2019/9/8 ??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 at redhat.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 at redhat.com>

And should I include

Tested-by: Jason Wang <jasowang at redhat.com>

?
> 
> 
> >