linux-kernel - Re: UBSAN: Undefined behaviour in block/blk-mq.c:1459:27 with pata

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Date:	Mon, 16 May 2016 09:55:31 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Meelis Roos <mroos@...ux.ee>
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	linux-ide@...r.kernel.org, linux-block@...r.kernel.org,
	Tejun Heo <tj@...nel.org>
Subject: Re: UBSAN: Undefined behaviour in block/blk-mq.c:1459:27 with
 pata_amd

On 05/13/2016 09:31 AM, Bartlomiej Zolnierkiewicz wrote:
> Does the patch below help?
>
> From: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
> Subject: [PATCH] blk-mq: fix undefined behaviour in order_to_size()
>
> When this_order variable in blk_mq_init_rq_map() becomes zero
> the code incorrectly decrements the variable and passes the result
> to order_to_size() helper causing undefined behaviour:
>
>   UBSAN: Undefined behaviour in block/blk-mq.c:1459:27
>   shift exponent 4294967295 is too large for 32-bit type 'unsigned int'
>   CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.6.0-rc6-00072-g33656a1 #22
>
> Fix the code by checking this_order variable for not having the zero
> value first.

Thanks Bart, added for 4.7.

-- 
Jens Axboe