linux-kernel - Re: [PATCH v2 2/7] Drivers: hv: vmbus: Avoid double fetch of msgtype in vmbus_on_msg

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Message-ID: <20201202134004.5tgrbyijrhvwwmk2@liuwe-devbox-debian-v2>
Date:   Wed, 2 Dec 2020 13:40:04 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Andrea Parri <parri.andrea@...il.com>
Cc:     Wei Liu <wei.liu@...nel.org>, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org,
        "K . Y . Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Juan Vazquez <juvazq@...rosoft.com>,
        Saruhan Karademir <skarade@...rosoft.com>
Subject: Re: [PATCH v2 2/7] Drivers: hv: vmbus: Avoid double fetch of msgtype
 in vmbus_on_msg_dpc()

On Wed, Dec 02, 2020 at 02:37:16PM +0100, Andrea Parri wrote:
> > > @@ -1072,12 +1073,19 @@ void vmbus_on_msg_dpc(unsigned long data)
> > >  		/* no msg */
> > >  		return;
> > >  
> > > +	/*
> > > +	 * The hv_message object is in memory shared with the host.  The host
> > > +	 * could erroneously or maliciously modify such object.  Make sure to
> > > +	 * validate its fields and avoid double fetches whenever feasible.
> > > +	 */
> > > +
> > >  	hdr = (struct vmbus_channel_message_header *)msg->u.payload;
> > > +	msgtype = hdr->msgtype;
> > 
> > Should READ_ONCE be used here?
> 
> I think it should.  Thank you for pointing this out.

Glad I can help.

The same comment applies to other patches as well, of course.

Wei.

> 
>   Andrea