thr3ads.net - Linux Virtualization - [BUG/RFC] vhost: net: big endian viring access despite virtio 1 [Jan 2017]

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Halil Pasic

2017-Jan-27 12:24 UTC

[BUG/RFC] vhost: net: big endian viring access despite virtio 1

On 01/26/2017 08:20 PM, Michael S. Tsirkin wrote:> On Thu, Jan 26, 2017 at 06:39:14PM +0100, Halil Pasic wrote:
>>
>> Hi!
>>
>> Recently I have been investigating some strange migration problems on
>> s390x.
>>
>> It turned out under certain circumstances vhost_net corrupts avail.idx
by
>> using wrong endianness.
[..]
>> -------------------------8<--------------
>> >From b26e2bbdc03832a0204ee2b42967a1b49a277dc8 Mon Sep 17 00:00:00
2001
>> From: Halil Pasic <pasic at linux.vnet.ibm.com>
>> Date: Thu, 26 Jan 2017 00:06:15 +0100
>> Subject: [PATCH] vhost: remove useless/dangerous reset of is_le
>>
>> The reset of is_le does no good, but it contributes its fair share to a
>> bug in vhost_net, which occurs if we have some oldubufs when stopping
and
>> setting a fd = -1 as a backend. Instead of doing something convoluted
in
>> vhost_net, let's just get rid of the reset.
>>
>> Signed-off-by: Halil Pasic <pasic at linux.vnet.ibm.com>
>> Fixes: commit 2751c9882b94 
>> ---
>>  drivers/vhost/vhost.c | 4 +---
>>  1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>> index d643260..08072a2 100644
>> --- a/drivers/vhost/vhost.c
>> +++ b/drivers/vhost/vhost.c
>> @@ -1714,10 +1714,8 @@ int vhost_vq_init_access(struct vhost_virtqueue
*vq)
>>         int r;
>>         bool is_le = vq->is_le;
>>
>> -       if (!vq->private_data) {
>> -               vhost_reset_is_le(vq);
>> +       if (!vq->private_data)
>>                 return 0;
>> -       }
>>
>>         vhost_init_is_le(vq);
> 
> 
> I think you do need to reset it, just maybe within vhost_init_is_le.
> 
>         if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
>                 vq->is_le = true;
> 	else
> 		vhost_reset_is_le(vq);
> 
> 
That is a very good point! I have overlooked that while the 
CONFIG_VHOST_CROSS_ENDIAN_LEGACY variant

static void vhost_init_is_le(struct vhost_virtqueue *vq)
{
        /* Note for legacy virtio: user_be is initialized at reset time
         * according to the host endianness. If userspace does not set an
         * explicit endianness, the default behavior is native endian, as
         * expected by legacy virtio.
         */
        vq->is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1) ||
!vq->user_be;
}

is fine the other variant 

static void vhost_init_is_le(struct vhost_virtqueue *vq)
{
        if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
                vq->is_le = true;
}
is a very strange initializer (makes assumptions about the state
to be initialized).

I agree, setting native endianness there sounds very reasonable.

I have a question regarding readability. IMHO the relationship
of reset_is_le and int_is_le is a bit confusing, and I'm afraid
it could become even more confusing with using reset in one of
the init_is_le's.

How about we do the following?

static void vhost_init_is_le(struct vhost_virtqueue *vq)
{
        if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
                vq->is_le = true;
+       else
+               vq->is_le = virtio_legacy_is_little_endian();

}

static void vhost_reset_is_le(struct vhost_virtqueue *vq)
{
-       vq->is_le = virtio_legacy_is_little_endian();
+       vhost_init_is_le(vq);
}

That way we would have correct endianness both after reset
and after init, I think :).

Thank you very much!

Halil

Greg Kurz

2017-Jan-27 13:37 UTC

head link

[BUG/RFC] vhost: net: big endian viring access despite virtio 1

On Fri, 27 Jan 2017 13:24:13 +0100
Halil Pasic <pasic at linux.vnet.ibm.com> wrote:
> On 01/26/2017 08:20 PM, Michael S. Tsirkin wrote:
> > On Thu, Jan 26, 2017 at 06:39:14PM +0100, Halil Pasic wrote:  
> >>
> >> Hi!
> >>
> >> Recently I have been investigating some strange migration problems
on
> >> s390x.
> >>
> >> It turned out under certain circumstances vhost_net corrupts
avail.idx by
> >> using wrong endianness.  
> 
> [..]
> 
> >> -------------------------8<--------------  
> >> >From b26e2bbdc03832a0204ee2b42967a1b49a277dc8 Mon Sep 17
00:00:00 2001
> >> From: Halil Pasic <pasic at linux.vnet.ibm.com>
> >> Date: Thu, 26 Jan 2017 00:06:15 +0100
> >> Subject: [PATCH] vhost: remove useless/dangerous reset of is_le
> >>
> >> The reset of is_le does no good, but it contributes its fair share
to a
> >> bug in vhost_net, which occurs if we have some oldubufs when
stopping and
> >> setting a fd = -1 as a backend. Instead of doing something
convoluted in
> >> vhost_net, let's just get rid of the reset.
> >>
> >> Signed-off-by: Halil Pasic <pasic at linux.vnet.ibm.com>
> >> Fixes: commit 2751c9882b94 
> >> ---
> >>  drivers/vhost/vhost.c | 4 +---
> >>  1 file changed, 1 insertion(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> >> index d643260..08072a2 100644
> >> --- a/drivers/vhost/vhost.c
> >> +++ b/drivers/vhost/vhost.c
> >> @@ -1714,10 +1714,8 @@ int vhost_vq_init_access(struct
vhost_virtqueue *vq)
> >>         int r;
> >>         bool is_le = vq->is_le;
> >>
> >> -       if (!vq->private_data) {
> >> -               vhost_reset_is_le(vq);
> >> +       if (!vq->private_data)
> >>                 return 0;
> >> -       }
> >>
> >>         vhost_init_is_le(vq);  
> > 
> > 
> > I think you do need to reset it, just maybe within vhost_init_is_le.
> > 
> >         if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
> >                 vq->is_le = true;
> > 	else
> > 		vhost_reset_is_le(vq);
> > 
> >   
> 
> That is a very good point! I have overlooked that while the 
> CONFIG_VHOST_CROSS_ENDIAN_LEGACY variant
> 
> static void vhost_init_is_le(struct vhost_virtqueue *vq)
> {
>         /* Note for legacy virtio: user_be is initialized at reset time
>          * according to the host endianness. If userspace does not set an
>          * explicit endianness, the default behavior is native endian, as
>          * expected by legacy virtio.
>          */
>         vq->is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1) ||
!vq->user_be;
> }
> 
> is fine the other variant 
> 
> static void vhost_init_is_le(struct vhost_virtqueue *vq)
> {
>         if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
>                 vq->is_le = true;
> }
> is a very strange initializer (makes assumptions about the state
> to be initialized).
> 
> I agree, setting native endianness there sounds very reasonable.
> 
> I have a question regarding readability. IMHO the relationship
> of reset_is_le and int_is_le is a bit confusing, and I'm afraid
> it could become even more confusing with using reset in one of
> the init_is_le's.
> 
> How about we do the following?
> 
> static void vhost_init_is_le(struct vhost_virtqueue *vq)
> {
>         if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
>                 vq->is_le = true;
> +       else
> +               vq->is_le = virtio_legacy_is_little_endian();
> 
> }
> 
> static void vhost_reset_is_le(struct vhost_virtqueue *vq)
> {
> -       vq->is_le = virtio_legacy_is_little_endian();
> +       vhost_init_is_le(vq);
> }
> 
> That way we would have correct endianness both after reset
> and after init, I think :).
> 
Yes, I think this is what we need.

Cheers.

--
Greg
> Thank you very much!
> 
> Halil
> 
>

Michael S. Tsirkin

2017-Jan-29 00:35 UTC

head link

[BUG/RFC] vhost: net: big endian viring access despite virtio 1

On Fri, Jan 27, 2017 at 02:37:47PM +0100, Greg Kurz
wrote:> On Fri, 27 Jan 2017 13:24:13 +0100
> Halil Pasic <pasic at linux.vnet.ibm.com> wrote:
> 
> > On 01/26/2017 08:20 PM, Michael S. Tsirkin wrote:
> > > On Thu, Jan 26, 2017 at 06:39:14PM +0100, Halil Pasic wrote:  
> > >>
> > >> Hi!
> > >>
> > >> Recently I have been investigating some strange migration
problems on
> > >> s390x.
> > >>
> > >> It turned out under certain circumstances vhost_net corrupts
avail.idx by
> > >> using wrong endianness.  
> > 
> > [..]
> > 
> > >> -------------------------8<--------------  
> > >> >From b26e2bbdc03832a0204ee2b42967a1b49a277dc8 Mon Sep 17
00:00:00 2001
> > >> From: Halil Pasic <pasic at linux.vnet.ibm.com>
> > >> Date: Thu, 26 Jan 2017 00:06:15 +0100
> > >> Subject: [PATCH] vhost: remove useless/dangerous reset of
is_le
> > >>
> > >> The reset of is_le does no good, but it contributes its fair
share to a
> > >> bug in vhost_net, which occurs if we have some oldubufs when
stopping and
> > >> setting a fd = -1 as a backend. Instead of doing something
convoluted in
> > >> vhost_net, let's just get rid of the reset.
> > >>
> > >> Signed-off-by: Halil Pasic <pasic at
linux.vnet.ibm.com>
> > >> Fixes: commit 2751c9882b94 
> > >> ---
> > >>  drivers/vhost/vhost.c | 4 +---
> > >>  1 file changed, 1 insertion(+), 3 deletions(-)
> > >>
> > >> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > >> index d643260..08072a2 100644
> > >> --- a/drivers/vhost/vhost.c
> > >> +++ b/drivers/vhost/vhost.c
> > >> @@ -1714,10 +1714,8 @@ int vhost_vq_init_access(struct
vhost_virtqueue *vq)
> > >>         int r;
> > >>         bool is_le = vq->is_le;
> > >>
> > >> -       if (!vq->private_data) {
> > >> -               vhost_reset_is_le(vq);
> > >> +       if (!vq->private_data)
> > >>                 return 0;
> > >> -       }
> > >>
> > >>         vhost_init_is_le(vq);  
> > > 
> > > 
> > > I think you do need to reset it, just maybe within
vhost_init_is_le.
> > > 
> > >         if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
> > >                 vq->is_le = true;
> > > 	else
> > > 		vhost_reset_is_le(vq);
> > > 
> > >   
> > 
> > That is a very good point! I have overlooked that while the 
> > CONFIG_VHOST_CROSS_ENDIAN_LEGACY variant
> > 
> > static void vhost_init_is_le(struct vhost_virtqueue *vq)
> > {
> >         /* Note for legacy virtio: user_be is initialized at reset
time
> >          * according to the host endianness. If userspace does not set
an
> >          * explicit endianness, the default behavior is native endian,
as
> >          * expected by legacy virtio.
> >          */
> >         vq->is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1) ||
!vq->user_be;
> > }
> > 
> > is fine the other variant 
> > 
> > static void vhost_init_is_le(struct vhost_virtqueue *vq)
> > {
> >         if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
> >                 vq->is_le = true;
> > }
> > is a very strange initializer (makes assumptions about the state
> > to be initialized).
> > 
> > I agree, setting native endianness there sounds very reasonable.
> > 
> > I have a question regarding readability. IMHO the relationship
> > of reset_is_le and int_is_le is a bit confusing, and I'm afraid
> > it could become even more confusing with using reset in one of
> > the init_is_le's.
> > 
> > How about we do the following?
> > 
> > static void vhost_init_is_le(struct vhost_virtqueue *vq)
> > {
> >         if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
> >                 vq->is_le = true;
> > +       else
> > +               vq->is_le = virtio_legacy_is_little_endian();
> > 
> > }
> > 
> > static void vhost_reset_is_le(struct vhost_virtqueue *vq)
> > {
> > -       vq->is_le = virtio_legacy_is_little_endian();
> > +       vhost_init_is_le(vq);
> > }
> > 
> > That way we would have correct endianness both after reset
> > and after init, I think :).
> > 
> 
> Yes, I think this is what we need.
> 
> Cheers.
OK, pls test this patch.
> --
> Greg
> 
> > Thank you very much!
> > 
> > Halil
> > 
> >

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