linux-kernel - Re: [PATCH 08/18] carl9170: prevent bounds-check bypass via speculative execution

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Message-ID: <113c7f80-265b-4da2-3eba-727c8f64a2b0@cogentembedded.com>
Date:   Sat, 6 Jan 2018 13:01:15 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Dan Williams <dan.j.williams@...el.com>,
        linux-kernel@...r.kernel.org
Cc:     linux-arch@...r.kernel.org, peterz@...radead.org,
        netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
        Elena Reshetova <elena.reshetova@...el.com>,
        gregkh@...uxfoundation.org,
        Christian Lamparter <chunkeey@...glemail.com>,
        tglx@...utronix.de, torvalds@...ux-foundation.org,
        Kalle Valo <kvalo@...eaurora.org>, alan@...ux.intel.com
Subject: Re: [PATCH 08/18] carl9170: prevent bounds-check bypass via
 speculative execution

Hello!

On 1/6/2018 4:10 AM, Dan Williams wrote:

> Static analysis reports that 'queue' may be a user controlled value that
> is used as a data dependency to read from the 'ar9170_qmap' array. In
> order to avoid potential leaks of kernel memory values, block
> speculative execution of the instruction stream that could issue reads
> based on an invalid result of 'ar9170_qmap[queue]'. In this case the
> value of 'ar9170_qmap[queue]' is immediately reused as an index to the
> 'ar->edcf' array.
> 
> Based on an original patch by Elena Reshetova.
> 
> Cc: Christian Lamparter <chunkeey@...glemail.com>
> Cc: Kalle Valo <kvalo@...eaurora.org>
> Cc: linux-wireless@...r.kernel.org
> Cc: netdev@...r.kernel.org
> Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---
>   drivers/net/wireless/ath/carl9170/main.c |    6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/ath/carl9170/main.c b/drivers/net/wireless/ath/carl9170/main.c
> index 988c8857d78c..0ff34cbe2b62 100644
> --- a/drivers/net/wireless/ath/carl9170/main.c
> +++ b/drivers/net/wireless/ath/carl9170/main.c
> @@ -41,6 +41,7 @@
>   #include <linux/module.h>
>   #include <linux/etherdevice.h>
>   #include <linux/random.h>
> +#include <linux/compiler.h>
>   #include <net/mac80211.h>
>   #include <net/cfg80211.h>
>   #include "hw.h"
> @@ -1384,11 +1385,12 @@ static int carl9170_op_conf_tx(struct ieee80211_hw *hw,
>   			       const struct ieee80211_tx_queue_params *param)
>   {
>   	struct ar9170 *ar = hw->priv;
> +	const u8 *elem;
>   	int ret;
>   
>   	mutex_lock(&ar->mutex);
> -	if (queue < ar->hw->queues) {
> -		memcpy(&ar->edcf[ar9170_qmap[queue]], param, sizeof(*param));
> +	if ((elem = nospec_array_ptr(ar9170_qmap, queue, ar->hw->queues))) {

    I bet this causes checkpatch.pl to complain. I don't see a dire need to 
upset it here, the assignment may well precede *if*...

> +		memcpy(&ar->edcf[*elem], param, sizeof(*param));
>   		ret = carl9170_set_qos(ar);
>   	} else {
>   		ret = -EINVAL;
> 

MBR, Sergei