Re: [PATCH 1/6] Drivers: hv: vmbus: Initialize memory to be sent to the host

[Andrea Parri]

On Sun, Dec 06, 2020 at 04:59:32PM +0000, Michael Kelley wrote:
> From: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx> Sent: Wednesday, November 18, 2020 6:37 AM
> > 
> > __vmbus_open() and vmbus_teardown_gpadl() do not inizialite the memory
> > for the vmbus_channel_open_channel and the vmbus_channel_gpadl_teardown
> > objects they allocate respectively.  These objects contain padding bytes
> > and fields that are left uninitialized and that are later sent to the
> > host, potentially leaking guest data.  Zero initialize such fields to
> > avoid leaking sensitive information to the host.
> > 
> > Reported-by: Juan Vazquez <juvazq@xxxxxxxxxxxxx>
> > Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx>
> > ---
> >  drivers/hv/channel.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
> > index 0d63862d65518..9aa789e5f22bb 100644
> > --- a/drivers/hv/channel.c
> > +++ b/drivers/hv/channel.c
> > @@ -621,7 +621,7 @@ static int __vmbus_open(struct vmbus_channel *newchannel,
> >  		goto error_clean_ring;
> > 
> >  	/* Create and init the channel open message */
> > -	open_info = kmalloc(sizeof(*open_info) +
> > +	open_info = kzalloc(sizeof(*open_info) +
> >  			   sizeof(struct vmbus_channel_open_channel),
> >  			   GFP_KERNEL);
> >  	if (!open_info) {
> > @@ -748,7 +748,7 @@ int vmbus_teardown_gpadl(struct vmbus_channel *channel, u32
> > gpadl_handle)
> >  	unsigned long flags;
> >  	int ret;
> > 
> > -	info = kmalloc(sizeof(*info) +
> > +	info = kzalloc(sizeof(*info) +
> >  		       sizeof(struct vmbus_channel_gpadl_teardown), GFP_KERNEL);
> >  	if (!info)
> >  		return -ENOMEM;
> > --
> > 2.25.1
> 
> This change is actually zero'ing more memory than is necessary.  Only the
> 'msg' portion is sent to Hyper-V, so that's all that needs to be zero'ed.
> But this code is not performance sensitive, and doing the tighter zero'ing
> would add lines of code with no real value.  So,
> 
> Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>

Thank you for the review.

Please notice that I posted a v2 of this series:

  https://lkml.kernel.org/r/20201202092214.13520-1-parri.andrea@xxxxxxxxx

Thanks,
  Andrea