linux-kernel - Re: UBSAN: Undefined behaviour in drivers/scsi/aic7xxx/aic7xxx

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Message-ID: <CAKb7Uvh8U1ncRg1jCnAVrdew=HyF+jNpY6=MknHgKyJmAdJEkw@mail.gmail.com>
Date:	Thu, 12 May 2016 17:56:04 -0400
From:	Ilia Mirkin <imirkin@...m.mit.edu>
To:	James Bottomley <jejb@...ux.vnet.ibm.com>
Cc:	Meelis Roos <mroos@...ux.ee>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Hannes Reinecke <hare@...e.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: UBSAN: Undefined behaviour in drivers/scsi/aic7xxx/aic7xxx_core.c:2831:31

On Thu, May 12, 2016 at 4:08 PM, James Bottomley
<jejb@...ux.vnet.ibm.com> wrote:
> On Thu, 2016-05-12 at 19:02 +0300, Meelis Roos wrote:
>> This is from a dual-AthlonMP 32-bit x86 system with onboard Adaptec
>> SCSI
>> controller, once during bootup.
>>
>> [    4.896307]
>> =====================================================================
>> ===========
>> [    4.896471] UBSAN: Undefined behaviour in
>> drivers/scsi/aic7xxx/aic7xxx_core.c:2831:31
>> [    4.896629] shift exponent -1 is negative
>
> Is this some sort of false positive?  The shift in question is
>
>         devinfo->target_mask = (0x01 << devinfo->target_offset);
>
> The code which calls this in ahc_linux_initialize_scsi_bus() looks to
> be looping from 0-16 (or variations).  Since the value passed in is
> unsigned, it would have to be set to ~0, which doesn't seem possible.

It's getting called from ahc_reset_channel, which does:

        ahc_compile_devinfo(&devinfo,
                            CAM_TARGET_WILDCARD,
                            CAM_TARGET_WILDCARD,
                            CAM_LUN_WILDCARD,
                            channel, ROLE_UNKNOWN);

drivers/scsi/aic7xxx/cam.h:#define      CAM_TARGET_WILDCARD ((u_int)~0)

  -ilia