linux-kernel - Re: [PATCH] iommu/vt-d: Fix shift overflow in qi_flush_dev

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Date:   Wed, 13 Dec 2017 08:58:47 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     iommu@...ts.linux-foundation.org, tursulin@...ulin.net,
        dwmw2@...radead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/vt-d: Fix shift overflow in qi_flush_dev_iotlb

On Wed, 13 Dec 2017 15:13:55 +0800
Peter Xu <peterx@...hat.com> wrote:

> On Tue, Dec 12, 2017 at 03:43:08PM -0700, Alex Williamson wrote:
> 
> [...]
> 
> > diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c
> > index 9a7ffd13c7f0..87888b102057 100644
> > --- a/drivers/iommu/dmar.c
> > +++ b/drivers/iommu/dmar.c
> > @@ -1345,7 +1345,9 @@ void qi_flush_dev_iotlb(struct intel_iommu *iommu, u16 sid, u16 qdep,
> >  	struct qi_desc desc;
> >  
> >  	if (mask) {
> > -		BUG_ON(addr & ((1 << (VTD_PAGE_SHIFT + mask)) - 1));
> > +		BUG_ON((mask > MAX_AGAW_PFN_WIDTH) ||
> > +		       ((mask == MAX_AGAW_PFN_WIDTH) && addr) ||
> > +		       (addr & ((1 << (VTD_PAGE_SHIFT + mask)) - 1)));  
> 
> Could it work if we just use 1ULL instead of 1 here?  Thanks,

In either case we're talking about shifting off the end of the
variable, which I understand to be undefined.  Right?  Thanks,

Alex