linux-kernel - Re: [PATCH] intel-iommu: Fix use after release during device attach

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Message-Id: <201011021557.24057.sheng@linux.intel.com>
Date:	Tue, 2 Nov 2010 15:57:23 +0800
From:	Sheng Yang <sheng@...ux.intel.com>
To:	Jan Kiszka <jan.kiszka@....de>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	iommu@...ts.linux-foundation.org,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] intel-iommu: Fix use after release during device attach

On Tuesday 02 November 2010 15:46:11 Jan Kiszka wrote:
> Am 02.11.2010 08:31, Sheng Yang wrote:
> > On Tuesday 02 November 2010 15:05:51 Jan Kiszka wrote:
> >> From: Jan Kiszka <jan.kiszka@...mens.com>
> >> 
> >> Obtail the new pgd pointer before releasing the page containing this
> >> value.
> >> 
> >> Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>
> >> ---
> >> 
> >> Who is taking care of this? The kvm tree?
> >> 
> >>  drivers/pci/intel-iommu.c |    2 +-
> >>  1 files changed, 1 insertions(+), 1 deletions(-)
> >> 
> >> diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
> >> index 4789f8e..35463dd 100644
> >> --- a/drivers/pci/intel-iommu.c
> >> +++ b/drivers/pci/intel-iommu.c
> >> @@ -3627,9 +3627,9 @@ static int intel_iommu_attach_device(struct
> >> iommu_domain *domain,
> >> 
> >>  		pte = dmar_domain->pgd;
> >>  		if (dma_pte_present(pte)) {
> >> 
> >> -			free_pgtable_page(dmar_domain->pgd);
> >> 
> >>  			dmar_domain->pgd = (struct dma_pte *)
> >>  			
> >>  				phys_to_virt(dma_pte_addr(pte));
> >> 
> >> +			free_pgtable_page(pte);
> >> 
> >>  		}
> >>  		dmar_domain->agaw--;
> >>  	
> >>  	}
> > 
> > Reviewed-by: Sheng Yang <sheng@...ux.intel.com>
> > 
> > CC iommu mailing list and David.
> > 
> > OK, Jan, I got your meaning now. And it's not the exactly swap. :)
> > 
> > I think the old code is safe, seems it's broken(exposed) by:
> > 
> > commit 1a8bd481bfba30515b54368d90a915db3faf302f
> > Author: David Woodhouse <David.Woodhouse@...el.com>
> > Date:   Tue Aug 10 01:38:53 2010 +0100
> > 
> >     intel-iommu: Fix 32-bit build warning with __cmpxchg()
> >     
> >     drivers/pci/intel-iommu.c: In function 'dma_pte_addr':
> >     drivers/pci/intel-iommu.c:239: warning: passing argument 1 of
> >     '__cmpxchg64'
> > 
> > from incompatible pointer typ
> > 
> >     It seems that __cmpxchg64() now cares about the type of its pointer
> >     argument, so give it a (uint64_t *) instead of a pointer to a
> >     structure which contains only that.
> >     
> >     Signed-off-by: David Woodhouse <David.Woodhouse@...el.com>
> > 
> > diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
> > index c9171be..603cdc0 100644
> > --- a/drivers/pci/intel-iommu.c
> > +++ b/drivers/pci/intel-iommu.c
> > @@ -236,7 +236,7 @@ static inline u64 dma_pte_addr(struct dma_pte *pte)
> > 
> >         return pte->val & VTD_PAGE_MASK;
> >  
> >  #else
> >  
> >         /* Must have a full atomic 64-bit read */
> > 
> > -       return  __cmpxchg64(pte, 0ULL, 0ULL) & VTD_PAGE_MASK;
> > +       return  __cmpxchg64(&pte->val, 0ULL, 0ULL) & VTD_PAGE_MASK;
> > 
> >  #endif
> >  }
> > 
> > Seems here is the only affected code?
> 
> CONFIG_64BIT is on here, so this change did not make a difference for me.

Oh...

Then it would due to most VT-d machine wouldn't run into while (iommu->agaw < 
dmar_domain->agaw). 

We have routing test for VT-d devices assignment, but seems we don't use this kind 
of VT-d machine for testing.

--
regards
Yang, Sheng


> 
> Jan
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