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To:     Jinbum Park <jinb.park7@gmail.com>, axboe@kernel.dk,
        bart.vanassche@wdc.com, jiufei.xue@linux.alibaba.com
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References: <20180728023058.GA21103@pjb1027-Latitude-E5410>
From:   "Gustavo A. R. Silva" <gustavo@embeddedor.com>
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Subject: Re: [PATCH v2] pktcdvd: Fix possible Spectre-v1 for pkt_devs
Message-ID: <0f94623c-47e2-31e6-50ac-1d11ba061411@embeddedor.com>
Date:   Fri, 27 Jul 2018 21:47:17 -0500
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On 07/27/2018 09:30 PM, Jinbum Park wrote:
> User controls @dev_minor which to be used as index of pkt_devs.
> So, It can be exploited via Spectre-like attack. (speculative execution)
> 
> This kind of attack leaks address of pkt_devs, [1]
> It leads an attacker to bypass security mechanism such as KASLR.
> 
> So sanitize @dev_minor before using it to prevent attack.
> 
> [1] https://github.com/jinb-park/linux-exploit/
> tree/master/exploit-remaining-spectre-gadget/leak_pkt_devs.c
> 
> Signed-off-by: Jinbum Park <jinb.park7@gmail.com>
> ---
> v2: Fix coding style by Gustavo.
> 
>  drivers/block/pktcdvd.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/block/pktcdvd.c b/drivers/block/pktcdvd.c
> index c61d20c..8ec2eaa 100644
> --- a/drivers/block/pktcdvd.c
> +++ b/drivers/block/pktcdvd.c
> @@ -67,8 +67,8 @@
>  #include <scsi/scsi.h>
>  #include <linux/debugfs.h>
>  #include <linux/device.h>
> -
>  #include <linux/uaccess.h>
> +#include <linux/nospec.h>
>  
>  #define DRIVER_NAME	"pktcdvd"
>  
> @@ -2231,6 +2231,7 @@ static struct pktcdvd_device *pkt_find_dev_from_minor(unsigned int dev_minor)
>  {
>  	if (dev_minor >= MAX_WRITERS)
>  		return NULL;
> +	dev_minor = array_index_nospec(dev_minor, MAX_WRITERS);

Adding a blank line here would be even better.

>  	return pkt_devs[dev_minor];
>  }
>  
> 

Acked-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

Thanks
--
Gustavo