linux-kernel - Re: [PATCH] scsi: mvumi: fix 32 bit shift of a 32 bit unsigned int

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Message-ID: <20190218093710.GB17104@kadam>
Date:   Mon, 18 Feb 2019 12:37:10 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Walter Harms <wharms@....de>
Cc:     Colin King <colin.king@...onical.com>,
        Jianyun Li <jyli@...vell.com>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: mvumi: fix 32 bit shift of a 32 bit unsigned int

On Sat, Feb 16, 2019 at 05:27:16PM +0100, Walter Harms wrote:
> Am 16.02.2019 15:44, schrieb Colin King:
> > From: Colin Ian King <colin.king@...onical.com>
> > 
> > Currently m_sg->baseaddr_h (a 32 bit unsigned int) is being shifted by a
> > total of 32 bits; this always produces a 0 result.  Fix this by casting
> > it to a dma_addr_t (a 64 bit unsigned int) before performing the shift.
> > 
> > Detected by CoverityScan, CID#147270 ("Operands don't affect result")
> > 
> > Fixes: f0c568a478f0 ("[SCSI] mvumi: Add Marvell UMI driver")
> > Signed-off-by: Colin Ian King <colin.king@...onical.com>
> > ---
> >  drivers/scsi/mvumi.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/scsi/mvumi.c b/drivers/scsi/mvumi.c
> > index 36f64205ecfa..d3582accfd09 100644
> > --- a/drivers/scsi/mvumi.c
> > +++ b/drivers/scsi/mvumi.c
> > @@ -313,7 +313,7 @@ static void mvumi_delete_internal_cmd(struct mvumi_hba
> > *mhba,
> >  			sgd_getsz(mhba, m_sg, size);
> >  
> >  			phy_addr = (dma_addr_t) m_sg->baseaddr_l |
> > -				(dma_addr_t) ((m_sg->baseaddr_h << 16) << 16);
> > +				(((dma_addr_t) m_sg->baseaddr_h << 16) << 16);
> >  
> >  			dma_free_coherent(&mhba->pdev->dev, size, cmd->data_buf,
> >  								phy_addr);
> 
> i would suggest to try a version with less casts to make it more readable
> like this untested suggestion:
> 
> phy_addr =(m_sg->baseaddr_h << 16)| m_sg->baseaddr_l;
> phy_addr <<= 16;
> 

That would be a behavior change but it also might be a bugfix?  Why
doesn't the code just do:

	phy_addr = ((dma_addr_t)m_sg->baseaddr_h << 32) | m_sg->baseaddr_l;

(Probably they broke it up into two shifts to silence a GCC warning that
the shift was wrong because of the missing cast?)

regards,
dan carpenter