Subject: Re: [PATCH v2 15/19] carl9170: prevent bounds-check bypass via speculative execution

From: Christian Lamparter <[email-masked]>
Date: Fri, 12 Jan 2018 15:42:28 +0100

On Friday, January 12, 2018 1:47:46 AM CET 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 <[email-masked]>
> Cc: Kalle Valo <[email-masked]>
> Cc: [email-masked]
> Cc: [email-masked]
> Signed-off-by: Elena Reshetova <[email-masked]>
> Signed-off-by: Dan Williams <[email-masked]>
> ---
This patch (and p54, cw1200) look like the same patch?! 
Can you tell me what happend to:

On Saturday, January 6, 2018 5:34:03 PM CET Dan Williams wrote:
> On Sat, Jan 6, 2018 at 6:23 AM, Christian Lamparter <[email-masked]> wrote:
> > And Furthermore a invalid queue (param->ac) would cause a crash in
> > this line in mac80211 before it even reaches the driver [1]:
> > |       sdata->tx_conf[params->ac] = p;
> > |                   ^^^^^^^^
> > |       if (drv_conf_tx(local, sdata, >>>> params->ac <<<<, &p)) {
> > |        ^^ (this is a wrapper for the *_op_conf_tx)
> >
> > I don't think these chin-up exercises are needed.
> 
> Quite the contrary, you've identified a better place in the call stack
> to sanitize the input and disable speculation. Then we can kill the
> whole class of the wireless driver reports at once it seems.
<https://www.spinics.net/lists/netdev/msg476353.html>

Anyway, I think there's an easy way to solve this: remove the 
"if (queue < ar->hw->queues)" check altogether. It's no longer needed
anymore as the "queue" value is validated long before the driver code
gets called. And from my understanding, this will fix the "In this case
the value of 'ar9170_qmap[queue]' is immediately reused as an index to
the 'ar->edcf' array." gripe your tool complains about.

This is here's a quick test-case for carl9170.:
---
diff --git a/drivers/net/wireless/ath/carl9170/main.c b/drivers/net/wireless/ath/carl9170/main.c
index 988c8857d78c..2d3afb15bb62 100644
--- a/drivers/net/wireless/ath/carl9170/main.c
+++ b/drivers/net/wireless/ath/carl9170/main.c
@@ -1387,13 +1387,8 @@ static int carl9170_op_conf_tx(struct ieee80211_hw *hw,
 	int ret;
 
 	mutex_lock(&ar->mutex);
-	if (queue < ar->hw->queues) {
-		memcpy(&ar->edcf[ar9170_qmap[queue]], param, sizeof(*param));
-		ret = carl9170_set_qos(ar);
-	} else {
-		ret = -EINVAL;
-	}
-
+	memcpy(&ar->edcf[ar9170_qmap[queue]], param, sizeof(*param));
+	ret = carl9170_set_qos(ar);
 	mutex_unlock(&ar->mutex);
 	return ret;
 }
---
What does your tool say about this? 

(If necessary, the "queue" value could be even sanitized with a
queue %= ARRAY_SIZE(ar9170_qmap); before the mutex_lock.)