linux-kernel - Re: [PATCH] virtio_bt: Fix alignment in configuration struct

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Message-ID: <20221007090223-mutt-send-email-mst@kernel.org>
Date:   Fri, 7 Oct 2022 09:03:02 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Igor Skalkin <igor.skalkin@...nsynergy.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        linux-bluetooth@...r.kernel.org, mgo@...nsynergy.com
Subject: Re: [PATCH] virtio_bt: Fix alignment in configuration struct

On Mon, Aug 08, 2022 at 02:04:43PM +0200, Igor Skalkin wrote:
> On 8/8/22 01:00, Michael S. Tsirkin wrote:
> 
>     On Mon, Aug 08, 2022 at 12:11:52AM +0200, Igor Skalkin wrote:
> 
>         According to specification [1], "For the device-specific configuration
>         space, the driver MUST use 8 bit wide accesses for 8 bit wide fields,
>         16 bit wide and aligned accesses for 16 bit wide fields and 32 bit wide
>         and aligned accesses for 32 and 64 bit wide fields.".
> 
>         Current version of the configuration structure:
> 
>             struct virtio_bt_config {
>                 __u8  type;
>                 __u16 vendor;
>                 __u16 msft_opcode;
>             } __attribute__((packed));
> 
>         has both 16bit fields non-aligned.
> 
>         This commit fixes it.
> 
>         [1] https://ddec1-0-en-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2fdocs.oasis%2dopen.org%2fvirtio%2fvirtio%2fv1.1%2fvirtio%2dv1.1.pdf&umid=d1786ace-e8ea-40e8-9665-96c0949174e5&auth=53c7c7de28b92dfd96e93d9dd61a23e634d2fbec-39b15885ceebe9fda9357320aec1ccbac416a470
> 
>         Signed-off-by: Igor Skalkin <Igor.Skalkin@...nsynergy.com>
> 
>     This is all true enough, but the problem is
>     1. changing uapi like this can't be done, will break userspace
>     2. the driver has more issues and no one seems to want to
>        maintain it.
>     I posted a patch "Bluetooth: virtio_bt: mark broken" and intend
>     to merge it for this release.
> 
> This is very sad. We already use this driver in our projects.

Ping. If we still have no maintainer I'm marking it broken, users
should at least be warned.


> Our virtio bluetooth device has two backends - HCI_USER socket backend for one
> platform and uart backend for the other, and works well (after applying your
> "[PATCH] Bluetooth: virtio_bt: fix device remove") patch, so this "device
> removal" problem can probably be considered solved .
> We could help with the rest of the problems you listed that can be solved
> (specification, QEMU support).
> And the only problem that is difficult to solve (because of the need to change
> UAPI header files) is just this one with unaligned configuration fields.
> At the moment, it does not reproduce, because without VIRTIO_BT_F_VND_HCI
> (Indicates vendor command support) feature negotiated, the driver does not
> read the non-aligned configuration fields.
> 
> So, what would you advise us to do? Continuing to use the "marked broken"
> driver, start writing a specification for a new from scratch, better one?
> Or is there any way to bring this one back to life?
> 
> 
> 
>         ---
>          include/uapi/linux/virtio_bt.h | 2 +-
>          1 file changed, 1 insertion(+), 1 deletion(-)
> 
>         diff --git a/include/uapi/linux/virtio_bt.h b/include/uapi/linux/virtio_bt.h
>         index a7bd48daa9a9..adc03709cc4f 100644
>         --- a/include/uapi/linux/virtio_bt.h
>         +++ b/include/uapi/linux/virtio_bt.h
>         @@ -23,9 +23,9 @@ enum virtio_bt_config_vendor {
>          };
> 
>          struct virtio_bt_config {
>         -       __u8  type;
>                 __u16 vendor;
>                 __u16 msft_opcode;
>         +       __u8  type;
>          } __attribute__((packed));
> 
>          #endif /* _UAPI_LINUX_VIRTIO_BT_H */
>         --
>         2.34.1
> 
> --
> 
> Best regards,
> 
> Igor Skalkin
> Software Engineer
> 
> OpenSynergy GmbH
> Rotherstr. 20, 10245 Berlin
> 
> igor.skalkin@...nsynergy.com
> www.opensynergy.com
> 
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