linux-kernel - RE: [PATCH 1/6] Drivers: hv: vmbus: Initialize memory to be sent to the host

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Date:   Sun, 6 Dec 2020 16:59:32 +0000
From:   Michael Kelley <mikelley@...rosoft.com>
To:     "Andrea Parri (Microsoft)" <parri.andrea@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        Juan Vazquez <juvazq@...rosoft.com>,
        Saruhan Karademir <skarade@...rosoft.com>
Subject: RE: [PATCH 1/6] Drivers: hv: vmbus: Initialize memory to be sent to
 the host

From: Andrea Parri (Microsoft) <parri.andrea@...il.com> 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@...rosoft.com>
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@...il.com>
> ---
>  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@...rosoft.com>