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

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Date:	Tue, 02 Nov 2010 08:46:11 +0100
From:	Jan Kiszka <jan.kiszka@....de>
To:	Sheng Yang <sheng@...ux.intel.com>
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

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.

Jan


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