linux-kernel - Re: [RFC PATCH 4/6] hv_sock: Initialize send_buf in hvs_stream

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Date:   Fri, 15 Apr 2022 08:50:41 +0200
From:   Andrea Parri <parri.andrea@...il.com>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Cc:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 4/6] hv_sock: Initialize send_buf in
 hvs_stream_enqueue()

> > @@ -655,7 +655,7 @@ static ssize_t hvs_stream_enqueue(struct vsock_sock *vsk,
> > struct msghdr *msg,
> > 
> >  	BUILD_BUG_ON(sizeof(*send_buf) != HV_HYP_PAGE_SIZE);
> > 
> > -	send_buf = kmalloc(sizeof(*send_buf), GFP_KERNEL);
> > +	send_buf = kzalloc(sizeof(*send_buf), GFP_KERNEL);
> 
> Is this change really needed?

The idea was...


> All fields are explicitly initialized, and in the data
> array, only the populated bytes are copied to the ring buffer.  There should not
> be any uninitialized values sent to the host.   Zeroing the memory ahead of
> time certainly provides an extra protection (particularly against padding bytes,
> but there can't be any since the layout of the data is part of the protocol with
> Hyper-V).

Rather than keeping checking that...


> It is expensive protection to zero out 16K+ bytes every time we send
> out a small message.

Do this.  ;-)

Will drop the patch.

Thanks,
  Andrea