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

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Date:	Tue, 2 Nov 2010 16:00:42 +0800
From:	Sheng Yang <sheng@...ux.intel.com>
To:	kvm@...r.kernel.org
Cc:	Jan Kiszka <jan.kiszka@....de>,
	Linux Kernel Mailing List <linux-kernel@...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 15:31:22 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()

In fact this one shouldn't affect the result. Wrong guess...

--
regards
Yang, Sheng

> 
>     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?
> 
> --
> regards
> Yang, Sheng
> --
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