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From:   "Michael Kelley (LINUX)" <mikelley@microsoft.com>
To:     Andrea Parri <parri.andrea@gmail.com>
CC:     KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
        Stefano Garzarella <sgarzare@redhat.com>,
        David Miller <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "virtualization@lists.linux-foundation.org" 
        <virtualization@lists.linux-foundation.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [RFC PATCH 4/6] hv_sock: Initialize send_buf in
 hvs_stream_enqueue()
Thread-Topic: [RFC PATCH 4/6] hv_sock: Initialize send_buf in
 hvs_stream_enqueue()
Thread-Index: AQHYT3fj0GpxS7gRakKuoVXd9R6gy6zvoDCwgADrHoCAAH/W8A==
Date:   Fri, 15 Apr 2022 14:30:29 +0000
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From: Andrea Parri <parri.andrea@gmail.com> Sent: Thursday, April 14, 2022 =
11:51 PM
>=20
> > > @@ -655,7 +655,7 @@ static ssize_t hvs_stream_enqueue(struct vsock_so=
ck *vsk,
> > > struct msghdr *msg,
> > >
> > >  	BUILD_BUG_ON(sizeof(*send_buf) !=3D HV_HYP_PAGE_SIZE);
> > >
> > > -	send_buf =3D kmalloc(sizeof(*send_buf), GFP_KERNEL);
> > > +	send_buf =3D kzalloc(sizeof(*send_buf), GFP_KERNEL);
> >
> > Is this change really needed?
>=20
> The idea was...
>=20
>=20
> > All fields are explicitly initialized, and in the data
> > array, only the populated bytes are copied to the ring buffer.  There s=
hould not
> > be any uninitialized values sent to the host.   Zeroing the memory ahea=
d of
> > time certainly provides an extra protection (particularly against paddi=
ng bytes,
> > but there can't be any since the layout of the data is part of the prot=
ocol with
> > Hyper-V).
>=20
> Rather than keeping checking that...

The extra protection might be obtained by just zero'ing the header (i.e., t=
he
bytes up to the 16 Kbyte data array).   I don't have a strong preference ei=
ther
way, so up to you.

Michael

>=20
>=20
> > It is expensive protection to zero out 16K+ bytes every time we send
> > out a small message.
>=20
> Do this.  ;-)
>=20
> Will drop the patch.
>=20
> Thanks,
>   Andrea