linux-kernel - Re: [PATCH v3 4/7] iommu: Switch gather->end to unsigned long long

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Date:   Thu, 17 Dec 2020 10:26:07 +0800
From:   Yong Wu <yong.wu@...iatek.com>
To:     David Laight <David.Laight@...LAB.COM>
CC:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        "Robin Murphy" <robin.murphy@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Tomasz Figa <tfiga@...gle.com>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "srv_heupstream@...iatek.com" <srv_heupstream@...iatek.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "youlin.pei@...iatek.com" <youlin.pei@...iatek.com>,
        Nicolas Boichat <drinkcat@...omium.org>,
        "anan.sun@...iatek.com" <anan.sun@...iatek.com>,
        "chao.hao@...iatek.com" <chao.hao@...iatek.com>,
        Greg Kroah-Hartman <gregkh@...gle.com>,
        "kernel-team@...roid.com" <kernel-team@...roid.com>
Subject: Re: [PATCH v3 4/7] iommu: Switch gather->end to unsigned long long

Hi David,

On Wed, 2020-12-16 at 11:03 +0000, David Laight wrote:
> From: Yong Wu
> > Sent: 16 December 2020 10:36
> > 
> > Currently gather->end is "unsigned long" which may be overflow in
> > arch32 in the corner case: 0xfff00000 + 0x100000(iova + size).
> > Although it doesn't affect the size(end - start), it affects the checking
> > "gather->end < end"
> > 
> > Fixes: a7d20dc19d9e ("iommu: Introduce struct iommu_iotlb_gather for batching TLB flushes")
> > Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> > ---
> >  include/linux/iommu.h | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > index 794d4085edd3..6e907a95d981 100644
> > --- a/include/linux/iommu.h
> > +++ b/include/linux/iommu.h
> > @@ -178,7 +178,7 @@ enum iommu_dev_features {
> >   */
> >  struct iommu_iotlb_gather {
> >  	unsigned long		start;
> > -	unsigned long		end;
> > +	unsigned long long	end;
> >  	size_t			pgsize;
> >  };
> 
> Doesn't that add two pad words on many 32bit systems?
> You probably ought to re-order the structure to keep the fields
> on their natural boundaries.
> 
> I'm not sure what is being mapped here, but could it make sense
> to just avoid using the highest addresses?
> Then you never hit the problem.

Thanks for your review. following Robin's suggesting, I will use "iova +
size - 1", then avoid this.

> 
> 	David
> 
> -
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