Re: [RFC PATCH 4/6] hv_sock: Initialize send_buf in hvs_stream_enqueue()

From: Andrea Parri <parri.andrea@gmail.com>
To: "Michael Kelley (LINUX)" <mikelley@microsoft.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()
Date: Fri, 15 Apr 2022 08:50:41 +0200	[thread overview]
Message-ID: <20220415065041.GC2961@anparri> (raw)
In-Reply-To: <PH0PR21MB3025F58A2536209ED3785F24D7EE9@PH0PR21MB3025.namprd21.prod.outlook.com>

> > @@ -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