Subject: Re: Coverity: mt7996_hw_queue_read(): Integer handling issues

From: Ryder Lee <[email-masked]>
Date: Sat, 3 Dec 2022 04:40:09 +0000

On Fri, 2022-12-02 at 14:11 -0800, coverity-bot wrote:
> Hello!
> 
> This is an experimental semi-automated report about issues detected
> by
> Coverity from a scan of next-20221202 as part of the linux-next scan
> project:
> 
https://urldefense.com/v3/__https://scan.coverity.com/projects/linux-next-weekly-scan__;!!CTRNKA9wMg0ARbw!jBOoj6LMqqA8E0AyjKQTa-0rVzcFiZ3BbpciEIn7so974kcMBeG4zZm-QU4AudLXY7-jNUSt0unzAt2zirSF$ 
>  
> 
> You're getting this email because you were associated with the
> identified
> lines of code (noted below) that were touched by commits:
> 
>   Thu Dec 1 17:29:14 2022 +0100
>     98686cd21624 ("wifi: mt76: mt7996: add driver for MediaTek Wi-Fi
> 7 (802.11be) devices")
> 
> Coverity reported the following:
> 
> *** CID 1527813:  Integer handling issues  (SIGN_EXTENSION)
> drivers/net/wireless/mediatek/mt76/mt7996/debugfs.c:460 in
> mt7996_hw_queue_read()
> 454     	for (i = 0; i < size; i++) {
> 455     		u32 ctrl, head, tail, queued;
> 456
> 457     		if (val & BIT(map[i].index))
> 458     			continue;
> 459
> vvv     CID 1527813:  Integer handling issues  (SIGN_EXTENSION)
> vvv     Suspicious implicit sign extension: "map[i].qid" with type
> "u8" (8 bits, unsigned) is promoted in "map[i].qid << 24" to type
> "int" (32 bits, signed), then sign-extended to type "unsigned long"
> (64 bits, unsigned).  If "map[i].qid << 24" is greater than
> 0x7FFFFFFF, the upper bits of the result will all be 1.
> 460     		ctrl = BIT(31) | (map[i].pid << 10) |
> (map[i].qid << 24);

u32 ctrl = BIT(31) | (map[i].pid << 10) | (map[i].qid << 24);

Hmm ...where's type "int" (32 bits, signed) from?

Ryder
> 461     		mt76_wr(dev, MT_FL_Q0_CTRL, ctrl);
> 462
> 463     		head = mt76_get_field(dev, MT_FL_Q2_CTRL,
> 464     				      GENMASK(11, 0));
> 465     		tail = mt76_get_field(dev, MT_FL_Q2_CTRL,